Aquatic and WetlandPlants of the ArnoldArboretum

Patricia A. Dalton andAlejandro Novelo R.

Illustrations by Amy Storey

In contrast to terrestrial plants, aquatic andwetland plants are not permanent in theirhabitats. Year after year we find that a

species that may be abundant m one yeardisappears in another. Because of fluctuatingwater levels, artificial destruction, pollu-tion, and modification of the surface soil,some species are unable to survive. Such dis-turbances also create new habitats thatallow alien species to become naturalized.As a result, we receive only glimpses of thecomplex relationships between the plantsand their environment. It is important,therefore, to document the flora of an areaover time, so that changes brought about byhuman modifications and environmentalfactors may be measured.The aquatic and wetland plants in the Ar-

boretum are unique in that their status hasbeen assessed from time to time throughoutthe history of the institution. E. J. Palmer’sSpontaneous Flora of the Arnold Ar-boretum, the first account of wild plants inthe Arboretum, was written in 1930. Palmer,who was a botanist on the staff of the Ar-

boretum, recorded the following species asgrowing m the meadow or in shallow waterat that time: calamus (Acorus calamus/, ),bur-reed (Sparganium eurycarpum St.John’s-wort (Hypericum majus), cardinalflower (Lobelia cardinahs great blue lobelia

(Lobelia siphilitica), waterweed (Elodeacanadensls/, two pondweeds (Potamogetonfoliosus and P. epihydrus~, and even a rareaquatic in the primrose family (Hottoma m-flata). Today not one of these plants can befound. Yet Palmer observed that even thenthe number of native species was decreasingrapidly in proportion to that of encroachingcultivated trees and shrubsThe term aquatic plant usually refers to

plants having a life cycle that revolvesaround water, being either completely sub-merged, emergent, or floating. Many defim-tions of this term exist, however, as theseplants exhibit a wide range of morphologicalexpression, and a clear distinction betweenwet and dry environments is often impossi-ble to achieve. Furthermore, in many areasthere are seasonal fluctuations of the water

table; for example, plants growing in drysoils most of the year may be flooded duringthe rainy season, and habitats with standingwater may dry out during the summermonths.Wetlands are transitional areas between

aquatic and terrestrial environments, wherethe water table is usually at or just below thesurface or where the land is covered by shal-low water. At the Arnold Arboretum themost familiar wetland type is what is termedwet meadow. Though the water table may

8

be slightly below the surface of the ground,the soil on these sites receives a continuous

supply of moisture. The vegetation includesgrasses, which are usually the dominantspecies, sedges, and other marsh plants suchas smartweeds, arrow-heads, rushes, andcat-tails. Like most meadows, these areaswould soon grow to trees and shrubs if theywere not mowed annually in the fall.One of the most familiar features of

aquatic vegetation is the zonation or se-quence of life forms, which is typically re-peated in lakes, ponds, canals, swamps, andslow-moving rivers that are not drasticallydisturbed by humans. An illustration of thiszonation may be found on page 9. The

emergent plants occupying the shoreline, ormarginal zones, are first in this sequence andare called attached emergent hydrophytes.These plants are attached to the substratewith a portion of the stem arising from thewater, for example, cat-tails (Typha), ins(Iris), and pickerelweed ~Pontederia/. All thereproductive parts of the plant are abovewater.

The next group in the sequence is those

plants found growing between the shorelineand the deeper waters, the transitional zone.This group includes three life forms. The at-tached floating-leaved hydrophytes are first.These plants are attached to the substrate,with the leaves floating on the surface of thewater, for example, water-lilies (Nymphaea)and water-chestnuts (Trapa). The reproduc-tive organs may be floating or emerging. Theattached submerged hydrophytes are sec-ond. These plants are attached to the sub-strate, and their vegetative parts are fullysubmerged, for example, pondweed(Potamogeton) and naiads (Najas/. The re-productive parts may be submerged, floating,or emerging. The third life form in the tran-

sitional zone is the attached floating-stemmed hydrophytes. These plants are at-tached to the substrate with the stems float-

ing on the surface of the water, for example,false loosestrife (Ludwigia) and some grassgenera. The leaves may be emerging or float-ing, and the reproductive organs are usuallyaerial.The last group is comprised of plants

growing in the deeper waters offshore. Thisincludes the free-floating hydrophytes andthe free submerged hydrophytes. Free-floating hydrophytes are unattached to thesubstrate, and their vegetative and repro-ductive organs float on the surface of the wa-

ter, for example, duckweed (Lemna), water-fern (Azolla), and water-hyacinth (Eichor-nia). Free submerged hydrophytes are plantsunattached to the substrate, with the vegeta-tive organs submerged and the reproductiveorgans emerging from the water. An exam-ple of this is the bladderwort (Utricularia).

Life forms of aquatic plants. Left to right:Attached floatmg-stemmed hydrophyte (Lud-wigia~; free-floating hydrophyte (Lemna Ii ,

free submerged hydrophyte /Utncularia/;attached submerged hydrophyte /Potamageton/;attached floating-leaved hydrophyte /Nymphaea/;and attached emergent hydrophytes (Typha andIris).

9

10

Broad-leaved Cat-tail: Typha latifoliaCat-tail Family: TyphaceaeCat-tail stands are a familiar sight through-out New England, especially along roadsideditches and other disturbed wetland areas. In

fact, the presence of cat-tails is often an in-dication of disturbance, as this species isamong the first to invade areas adversely af-fected by human activities. Cat-tails are tol-erant of a wide range of soil and water condi-tions and spread rapidly, often as much as 17 7feet per year. Whole colonies may be up-rooted by water, wind, and animals, butloose parts are carried to other bodies ofwater and become firmly established. Thespecies is found over most of temperateNorth America, Europe, and eastern Asia. Atthe Arboretum it can be seen in extensivestands in the meadow, along the margins ofthe three ponds, and on the banks of BusseyBrook.A rooted, emergent hydrophytic plant,

this cat-tail grows up to 7 feet tall, with long,stout rhizomes submerged in the mud. Thelight green leaves, which are erect, flat,linear, and elongate, emerge from the water,with a sheath closely enveloping the lowerpart of the stem. The inflorescence is a

dense, cyclindrical spike, which has twoportions, the upper containing the staminateflowers and the lower the pistillate flowers.The staminate flowers are ephemeral, whilethe pistillate flowers are persistent, with thefruit forming a dark brown, showy spikewith hairy fruits up to 7 inches long and 2inches wide. These small single-seededfruits are produced in great numbers, up to20,000 to 70,000 per inflorescence. Typha iswind pollinated and produces powderypollen.Cat-tail can be cultivated as a fiber crop on

lands that are too wet for other purposes.Although little is known of its pulping qual-ities, methods of using the stems and leavesof this plant are now being developed forpaper-making. In the 18th and 19th cen-turies papermaking from cat-tails was aflourishing industry in New York. Today thesoft fiber is used in making mats, chair seats,baskets, and other woven articles.

Water-Plantain: Alisma subcordatumWater-Plantain Family: Alismataceae

The genus Alisma, in the family Alis-mataceae (water plantams), was once ofgreat interest to botanists because it was

thought to be among the most primitivemonocotyledons (plants having a single seedleaf), perhaps derived from aquatic dicotyle-dons (plants having 2 seed leaves) best rep-resented in the order Nymphaeales. How-ever, evidence now shows that the Alis-mataceae are not primitive but highly spe-cialized, with complex vegetative organiza-tion and floral development. Two species,Alisma triviale andAlisma subcordatum,are frequent on mudflats, in shallow watersof the ponds, and along Bussey Brook at theArnold Arboretum. The genus Alisma is

widely distributed throughout the UnitedStates.

Water-plantain is an emergent hydrophyt-ic plant with a basal cluster of long-petioledleaves surrounding the flower stalk. Theleaves exhibit a wide variety of patterns andmay be slender to broadly ovate. In rare in-stances the leaves are reduced to ribbonlikestructures. The inflorescence is a large pani-cle with whorled branches bearing many

11 I

Common Cat-Tail (Typha latifoha~ I

12 z

Water-Plantam ~Ahsma subcordatum)

13

small perfect flowers. The 3 broadly ovategreen sepals are persistent and surround the3 small pinkish petals. Six stamens and ap-proximately 10 to 25 pistils are arranged in aring on a flattened receptacle. The fruit ofAlisma is an achene (dry, indehiscent, andone-seeded) with one or two grooves and aminute ascending beak. It has been statedthat dormancy in the seeds is due to themechanical restraint of the seed coat, whichallows the seeds to lie in water for yearswithout losing their viability.

Water-plantain secretes nectar, whichmay attract such pollinators as flies andshort-tongued bees. Unlike those of mostplants, the anthers in all the flowers dehisceat about the same time, so pollen is availablefor only a short period of time.

Duck-Potato: Sagittaria latifoliaWater-Plantain Family: AlismataceaeA botanist on the Lewis and Clark Expeditionobserved an Indian woman collecting duck-potato (Saglttaria latifolia) roots from a canoenear the mouth of the Columbia River. Thewoman would paddle out to where the waterwas breast high and use her toes to separatethe tuber from the root. The tuber, about thesize of a hen’s egg, would then float to the top,and the woman would throw it into a basketin the canoe. Although duck-potato is nolonger eaten by human beings, it is of con-siderable value to wildlife and has been

planted as a source of both food and shelterfor wildfowl.

The species ranges from Nova Scotia andBritish Columbia southward to Mexico. Atthe Arnold Arboretum it is common m themeadow and along pond margins and Bussey

Brook. It blooms from July through Sep-tember.

This rooted, emergent hydrophytic plantreaches 3 feet tall, with its root submerged inthe mud. Duck-potato is a perennial thatoverwinters by means of tubers. In late sum-mer and early fall the stolons (elongate under-ground stems) begin to produce terminal tu-bers by an enlargement of the 2 or more short,thickened intemodes next to the apical bud.The tubers, now full of starch, are enclosed byscale leaves and are deeply embedded in thesoil.

Like many aquatic plants, the duck-potato, or arrow-head, exhibits many bewil-dering morphological variations within vari-ous habitats, which for the duck-potato mayinclude pond margins, lakes, swamps, andsluggish streams. The emergent, longpetioles produce leaves that are generallyarrow-shaped but may also be linear to ovatein form. Accompanying the leaves is aninflorescence composed of whorls of flowersthat are usually arranged with the upperwhorls staminate and the lower pistillate.There may be as many as 10 or more whorls

per inflorescence, and each flower is com-posed of 3 sepals and 3 showy white petals.The fruits are in a dense head and arebeaked.

14

Duck-Potato (Sagittana latifoha)

15 s

Arrow-Arum: Peltandra virginicaArum Family: Araceae

The starchy root from which arrow-arum(Peltandra virginica) grows was once eatenby the Indians in Virginia, who called theplant tuckaho. The root, which is extremelyacrid and poisonous, was steamed m aheated pit, covered over with earth, and leftundisturbed for a day or two. This processbroke down the crystals of calcium oxalatethat make the plant poisonous. The driedroots were then ground up into meal.Arrow-arum ranges from Florida to Texas,

north throughout New England and intoCanada. At the Arboretum it grows in shal-low waters in the three ponds and along Bus-sey Brook.This rooted, emergent hydrophytic plant

is produced from a stout, spongy rootstock.The leaves are quite variable in form but areusually arrow shaped with wavy margins.The leaves of arrow-arum may be easily con-fused with those of duck-potato (Sagittarialatifolia). However, the leaves of arrow-arum have only 3 distmct nerves, whilethose in the duck-potato have more than 3.The inflorescence is similar in appearance tosuch familiar members of the arum family asskunk cabbage (Symplocarpus foetidus) andwild calla (Calla palustris). The long, greenspathe almost conceals the whitish clublikespadix, which is completely covered withmany minute flowers. The basal portion ofthe spadix contains the pistillate or femaleflowers, while the upper portion containsthe staminate or male flowers. Green berriesare produced in the fall. This plant has anefficient way of planting its seeds. The stalk,covered by the leathery green spathe, curvesand grows downward, driving the seeds intothe soft mud.

Pickerelweed: Pontederia cordataPickerelweed Family: Pontederiaceae

Pontederia is a small genus of aquatic plantsdistributed throughout subtropical andtemperate regions of North America. Pon-tederia cordata, pickerelweed, is restrictedto the eastern provinces of Canada and theeastern to midwestern United States, withits greatest concentration along the Atlanticcoastal plain and the Great Lakes Region. Itgrows in saltwater marshes along the coastand in fresh water inland. It is common inthe ponds at the Arnold Arboretum andblooms from July to late September.This rooted, emergent hydrophytic plant

has rhizomes that are short, thick, and pros-trate in the mud. Reproduction occurs whenrhizomes break and form new growths. Thelong-petioled leaves, up to 9 inches long and5 inches wide, are quite variable in form butare parallel veined and usually heart-shaped.The showy inflorescence is a spike of deeppurplish blue flowers, each having a yellowspot at the base of the upper perianth lobes.Pickerelweed is one of the few plants thatexhibit three flower forms of the same

species. The three forms are: plants withthree medium stamens, three long stamens,and a short style; plants with three shortstamens, three long stamens, and a mediumstyle; plants with flowers having three shortstamens, three medium stamens, and a

long style. The three forms ensure cross-pollination. Pollen transfer from a stamen toa pistil of equivalent length appears to bemore productive of seeds than pollen trans-fer from a stamen to a pistil of unequallength. The fruits are small, winged withseveral longitudinal ridges, and very buoy-ant. Travel by water is thought to be thisplant’s main mode of long-distance dispersal.

16 6

Arrow-Arum ~Peltandra vmgmica)

17 7

Pickerelweed (Pontedena cordata) /

18

Common Blue Flag: Iris versicolorIris Family: Iridaceae

The common blue flag /Iris versicolor) is amember of the family of plants aptly namedafter Iris, the Greek goddess of the rainbow.This beautiful blue-violet flower has 3 broadrecurved sepals (the falls) boldly veined withgreen, white, and yellow, and 3 smallererect, slender petals (the standards).This species is a gregarious one. Plants are

rarely found as isolated individuals, andsingle colonies of up to several hundred havebeen observed. The range of the blue flag inNorth America coincides with the northern

range of the white pine (Pinus strobus), ),comprising New England, New York,Pennsylvania, northern Ontario, and north-ern Michigan. The plant prefers moist soilsbut also grows in standing water. The blueflag blooms from May through June at theArboretum and is common in the meadow

and along pond margins and Bussey Brook.This rooted, emergent hydrophytic plant

has stems up to 3 feet long. The long, narrowleaves are pale green to grayish and sheathedat the base. In the absence of the flowers, theleaves of the blue flag can easily be confusedwith those of the cat-tail (Typha latifolia).The blue-flag leaves are straight and tightlyfolded, while those of the cat-tail are flat andslightly twisted at the top.The greenish fruit of the blue flag is 3

angled and up to 11/z inches long and 1 inchwide. The seeds float readily and travel bywater, spreading themselves along lake andriver margins.

Yellow Iris: Iris pseudacorusIris Family: IridaceaeThe lovely yellow iris is believed to be thesource of the fleur-de-lis of the French heral-dic shield, which dates from the 12th cen-tury.

The Iris genus is found throughout thetemperate regions of the northern hemi-sphere. It contains 300 species, of which 10are aquatic.The yellow iris was introduced to Canada

from Eurasia and Africa and escaped fromcultivation, spreading to freshwater wet-lands to such an extent as to give the appear-ance of a native plant. It is also believed tohave been cultivated in this country duringColonial times. The first record of an es-

capee dates from 1911 in Newfoundland. By1915 the species was found in Nova Scotia,and it eventually became established inBritish Columbia, Quebec, Ontario, andPrince Edward Island.Yellow iris has become an aggressive weed

in parts of the eastern United States fromMassachusetts south to Virginia and west toWisconsin. It is common in the meadow and

along pond margins and Bussey Brook at theArnold Arboretum and blooms from May toJuly.A rooted, emergent hydrophytic plant, the

yellow iris grows to 3 feet tall, arising fromlong, creeping, stout rhizomes. The leavesoften form clumps emerging from the waterand are dark green, slender, up to 1 inchwide, and parallel veined. The flower stalk iserect, about as tall as the leaves, and pro-duces 1 to 2 flowers at the apex in the axilsof the small upper leaves. The 2 involucralbracts are shorter than the showy, bright yel-low flowers, which are composed of 3 outerrecurved sepals and 3 yellow inner petals,slender, to 4 inches long. The sepals have

19

Common Blue Flag (Ins versicolor)

20

IYellow Ins (Ins pseudacorus/

.

21

delicate brown lines or flecks at the base andon the claw. The fruit capsule is bright greenand often lustrous. It is bluntly 3-angled andcontains somewhat round corky seeds.

Swamp Loosestrife: Decodonverticillatus

Loosestrife Family: LythraceaeThe genus Decodon is monotypic, that is, itincludes only one species, Decodon verticil-latus, swamp loosestrife. This species growsonly in the United States, ranging from Lou-isiana to Florida and northwards to Min-nesota and Maine. Fossil material has beenfound in Asia and Europe. At the Arboretumthe swamp loosestrife grows in the pondnear the lilacs and blooms from July to Oc-tober.

Swamp loosestrife, or water willow, as itis also called, has a unique way of reproduc-ing. The stems, which can reach 6 to 8 feetin height, are weak and remain upright foronly a short time before bending over. Whenthe apex of the stem touches the surface ofthe water, swelling occurs, and aerenchyma(spongy tissue with large air spaces) devel-ops, producing adventitious roots that an-chor it. Thus, a new offshoot is establishedsome distance from the mother plant.This rooted, emergent hydrophytic herb,

or short-lived shrub, has four- to six-sidedstems. The bark of the submerged parts isspongy and thick. The leaves are short-

stalked, opposite or whorled, slender, andpointed at the tip. The upper leaves haveclusters of 1 to 3 flowers in their axils. Likeother members of the loosestrife family, the

flowers are trimorphous. The petals arebright magenta and crinkly. The number ofstamens is usually twice the number of pet-als. The stamens vary in length and are ar-ranged in two whorls. The fruit is a capsule.

Fragrant Water-Lily: Nymphaeaodorata

Water-Lily Family: Nymphaeaceae

Growing in stagnant and muddy water, it burstsup so pure and fair to the eye and so sweet to the

scent, as if to show us what purity and sweetnessreside in and can be extracted from the slime andmuck of earth.

Henry David ThoreauSummer: From the journalof Henry Damd Thoreau

The buds of the fragrant water-lily (Nym-phaea odorata) open in early morning, ex-posing the spectacular white, waxy flowers,which float on the surface of the water.Some flowers fold up their petals during theearly afternoon, while others remain open.In addition to its other attractions, the fra-

grant water-lily has a long blooming season,from June through September. This speciesis native to southern Canada, the UnitedStates, Central America, and South Americaand is common in all three ponds at the Ar-boretum.This attached floating-leaved hydrophytic

plant has a thick, fleshy rhizome that issubmerged in the mud and may be long- orshort-lived and creeping or branching. Thefloating, rounded leaves are up to 10 incheswide and are attached by long rubberlikepetioles that vary in length according to thewater depth. The blades are green and glossyabove and purplish on the underside. The

22 .

Swamp Loosestrife (Decodon vertlcillatus/

23

Fragrant Water-Lily (Nymphaea odorata)

24

solitary, sweet-smelling flowers, up to 6inches wide, have 4 sepals followed by nu-merous spirally arranged petals passinggradually into stamens. The stamens cannumber from 36 to 100 and the pistils up to20. When the petals have withered, theflower stalk forms a spiral shape underwaterand develops a green fleshy fruit in or nearthe substrate. The seeds emerge when thefruit decays and spread by floating. Thisspecies can form dense stands rapidly.

Water-Chestnut: Trapa natansWater-Chestnut Family: Trapaceae

The water-chestnut (Trapa natans) has alsobeen known as water caltrop because of thesharp points on its fruit. A caltrop was asmall bronze or iron ball with projectingspikes that Roman soldiers in battle placedin the path of their foe to incapacitate thehorses. Although the wounds from a water-chestnut are not incapacitating, they arepainful.This rooted, floating-leaved aquatic plant

is native to Europe. Introduced into theUnited States in 1884, it has become locallyabundant in the eastern part of the country,so much so that it is now a nuisance, form-ing impenetrable mats that spread rapidlyand hinder navigation, prevent fishing, andovercrowd more desirable plants (e.g., bur-reed (Sparganium eurycarpum~. State andfederal laws prohibit the importation andtransportation of this species. The water-chestnut used in Chinese cooking in thiscountry is the edible corm of the sedgeEleocharis dulcis.The stem of the water-chestnut plant is

rooted in the mud and has slender leaves

variable in form. The lower, submergedleaves are sessile, alternate, and deeply di-vided into many threadlike segments, whilethe floating, glossy leaves, with inflatedpetioles and toothed, diamond-shapedblades, form a rosette at the end of eachbranch. The inconspicuous, solitary flowersare short stalked in the axils of the leavesand consist of 4 green sepals and 4 whitepetals. They bloom from July to late August.The fruit is brownish and nutlike.

Pepperwort: Marsilea quadrifoliaPepperwort Family: Marsileaceae

A small group of ferns came into existence

during the great rise of the flowering plantsat the end of the Cretaceous period, 300 mil-lion years after the genesis of other majorfern groups. These ferns adapted to a wateryenvironment, and growth in water is stillnecessary for the completion of certainstages in their life cycle. Pepperwort, orwater-clover (Marsilea quadrifolia), is amember of this unusual group. The genusMarsilea contains about 65 species growingthroughout the warmer regions of the world.Marsilea quadrifolia was first introducedfrom Europe into this country via BantanLake in Connecticut in 1862. It has spreadthroughout New England and into the mid-western states and is common at the Ar-boretum.This species is a rooted, floating-leaved

hydrophyte that increases in size with thelevel of the water. The slender, threadlikerhizomes creep slightly below the mud andgive rise to a delicate, shamrock-shaped leafthat may float on the water surface or standerect above the water.

25

Water-Chestnut /Trapa natans)

26

Pepperwort (Marsilea quadmfolia)

27

Unlike most ferns, which generally pro-duce their spores in clusters on the under-side of the leaf or frond, the water-cloverhouses its spores in 1 or 2 hard, brown bean-shaped structures known as sporocarps.These sporocarps are produced on a slenderbrownish stalk that rises near the base of theleaf stalk. Each sporocarp has many com-

partments, each containing numerousspores. When the spores are mature, the cap-sule bursts open vertically into halves, ex-posing the compartments, which are linkedby a gelatinous ring. This ring floats on thewater with the spore masses attached.

Duckweed: Lemna minorDuckweed Family: LemnaceaeThe green mantle of the stagnant pool

- William Shakespeare King Lear

In 1936 a strange phenomenon occurred inthe Sudbury and Charles Rivers in Massa-chusetts. "Millions of Small Plants CoverCharles" one newspaper headline read."Millions of tiny plants, resembling sham-rocks in color and appearance turned the sur-

face of the 5 miles of the Auburndale sectionof the Charles River bright green yesterday," "

the article reported. It was soon discoveredthat the same condition existed in the Sud-

bury, yet the two rivers had no connectionwhatever.The green phenomenon proved to be an

explosion of the duckweed plant /Lemnaminor), one of the world’s smallest floweringplants, and its causes have never been fullyunderstood. It is believed today that a corre-lation exists between the spread of duck-weed and the presence in the water ofsoluble nitrates from sewage. Soluble ni-

trates turn the naturally acidic waters ofeastern Massachusetts nearly neutral, acondition that is favorable to duckweed.The genus Lemna is found throughout the

world. Lemna minor is common in drainageditches and in the meadow at the Ar-boretum.This plant is a free-floating aquatic herb

consisting of a single body called a frond orthallus. This small, flat oval, rarely over’/ainch long, is not differentiated into leaves orstem. It is often purplish beneath with asingle root attached to each segment. Thethallus reproduces asexually by buds form-ing groups of two or more plant bodies thatoften remain attached. The inflorescence isnaked or enclosed in a membranous spathe;it is comprised of one pistillate flower, con-sisting solely of one pistil, and two stami-nate flowers, each consisting solely of onestamen.

Despite its unpleasant appearance,duckweed may have significant potential asa crop plant in the tropics and the sub-tropics, where its growth is profuse. Analy-ses show that its nutritive value in bothhuman and animal diets exceeds that ofmost agricultural plants; it is high in proteinand amino acids. Wolffia, a genus in thesame family, contains a species that is eatenin northern Thailand. The Thais call it "eggsof the water."

Common Bladderwort: Utricularia

vulgarisBladderwort Family: Lentibulariaceae

Common bladderwort (Utricularia vulgaris)is among the comparatively few species ofcarnivorous plants. Each tiny bladder on the

28

Duckweed (Lemna mmor/

29

underwater stem has an opening that func-tions as a trap door. The "door" is pressuresensitive and when touched opens in 11250thof a second. When the prey enters, the door

closes, trapping it within. Even when it istoo large to be contained inside the bladder,the prey is often held at the opening andingested by the plant over time. The smal-lest traps can catch microscopic single-celled protozoans and rotifers, while largertraps can catch fish fry, water fleas, andmosquito larvae. Small aquatic plants, suchas duckweed (Lemna) and watermeal(Wol f fia also have been found in the blad-ders.Common bladderwort is distributed

throughout the eastern and midwesternUnited States and north to southern Lab-rador and Alaska. Although it is common inNew England, it was found at the Arboretumfor the first time only last year, growing inshallow water in the smallest pond.This free, submerged hydrophytic plant

lacks roots and grows freely and unattachedin the water, usually just beneath the sur-face. The plant overwinters by formingsmall clusters of crowded modified leaves

called turions. In cold regions, where theplant must lie dormant for several monthsand produce winter buds, it usually bearsfewer flowers or none at all and producesfruit infrequently. The much dissected seg-ments produce numerous bladders, and atthe height of the summer as many as 100 canbe seen on a single segment.The erect scape arising above the water

supports as many as 20 yellow flowers thatresemble small snapdragons. The broad,somewhat lobed lower lip is delicatelystriped in brown and orange and is shorterthan the curved spur. The seeds are brown

and lustrous. See page 2 for illustration.

Skunk Cabbage: Symplocarpus foetidusArum Family: Araceae

Skunk cabbage (Symplocarpus foetidus) isone of the plants in the Araceae family thatproduce enough heat to render themselveswarmer than the surrounding air. An unusu-ally high rate of respiration in these plants isresponsible for the heat, which in the skunkcabbage is retained by the spongy tissue ofthe spathe. During the early stages of bloom-ing, the clublike central spadix maintains atemperature of 36°F to 63°F higher than thesurrounding air (Knutson 1979) for as long astwo weeks. This period coincides with thematuration of pollen and egg cells, and theheat helps to attract such pollinators as bees.Although honeybees do not fly well if airtemperature is below 65°F, they are knownto visit skunk cabbage at temperatures aslow as 42°F (Knutson 1979). The sweetishscent of the uninjured spathe may also at-tract bees. The offensive odor of the spathewhen damaged is believed to attract insectpollinators.The genus Symplocarpus has two widely

disjunct areas of distribution: one in easternNorth America, ranging from Quebec andNova Scotia south through New England toGeorgia and Tennessee and west to Min-nesota and Iowa; the other is in eastern Asia.

Individual skunk cabbage plants areknown to endure for a very long time, possi-bly even longer than the giant redwoods(Knutson 1979). The species is also presentin Japan and on the eastern edge of the Asiancontinent. It grows in swamps, muddyground, wet meadows, woods, and alongstream banks, often in dense stands. It is notcommon at the Arboretum, but it can befound in moist, low-lying areas in themeadow along with cat-tails and irises.

30

Skunk Cabbage (Symplocarpus foetidus)

31

This perennial herb produces many large,clustered basal leaves, which appear as thespathe matures. These leaves, which may beup to 4 feet in length, are ovate and con-spicuously veined. The flower buds developon the underground rootstocks. By winter,shoots several inches in length emerge, withone flower bud per shoot forming as lateraloffshoots of the leaf bud. Occasionally, theflower buds are lacking and the leafy shootappears alone. The inflorescence, which isunique to the arum family, consists of thecream-colored spadix subtended by thefleshy green-purple or brown-spotted spathe.Many individual flowers cover the spadix,each comprising 4 perianth segments and 4fleshy stamens opposite the segments. Theseeds are embedded in the enlarged, spongyspadix.

Purple Loosestrife: Lythrum salicariaLoosestrife Family: Lythraceae

Purple loosestrife (Lythrum salicaria), one ofthe more recent additions to the list of nui-sance plants, is native to the eastern hemi-sphere, Eurasia, North Africa, and Aus-tralia. Palmer, in The Spontaneous Flora ofthe Arnold Arboretum 1930/, described theplant as "common in low meadows andabout ponds and sometimes in drier wasteground." Today it forms massive, spectacu-lar colonies in the meadow, around pondmargins, and along Bussey Brook and iseliminating some of the native wetlandspecies.Records show that by the late 19th and

early 20th centuries this species had spreadinto the glaciated wetlands of North Amer-ica and had become an aggressive weed in

some areas, particularly in the Great LakesRegion, the St. Lawrence River Valley, andthe Hudson River Valley. South of the Wis-consin glacial border, however, it is scat-tered.The first report of Lythrum salicaria in

North America was in Pursh’s Flora Amer-

icae Septentrionalis in 1814. Two eminentbotanists, John Torrey and Asa Gray, weredoubtful of the previous records, and Graywrote in 1856 that its status as a native plantwas "not clear." It was not until 1890, whenthe sixth edition of Gray’s Manual of Botanywas published, that the species was treatedas a plant naturalized from Europe and there-fore a nonindigenous member of the NorthAmerican flora.The first record of the plant in Massachu-

setts dates from 1844 in Cambridge. By1900, purple loosestrife was recorded in sev-eral localities throughout the state, and it isbelieved to have been introduced in the Mer-rimac River Valley through seed washed outof wool at a plant near Abbots Mill atGraniteville.The stem of this perennial grows to 5 feet,

produces narrow, sessile leaves that are op-posite to whorled and heart shaped at thebase. The purplish red flowers are borne in acolorful spikelike panicle, up to 1 foot long,and bloom from June to late August. The

perianth lobes vary in number from 4 to 6with stamens either equal to or twice thenumber of the petals.

32

Purple Loosestrife (Lythrum sahcama)

33

Drooping Sedge: Carex crinitaSedge Family: Cyperaceae

Although the hairy-looking spike droopingfrom the top of the stem of the sedge is notusually recognized as such, it is in fact acluster of flowers, and the sedges belong to aflowering plant family, the Cyperaceae.Sedges are further designated as monocots,because they produce a single seed-leaf upongermination. Other monocots include irises,lilies, orchids, and rushes.The drooping sedge (Carex crinita) is dis-

tributed throughout the eastern and south-eastern United States and is the most com-mon wetland species at the Arboretum. Itgrows in large clumps in the meadow andalong pond margins and Bussey Brook.Members of the sedge family are often mis-

taken for grasses (Gramineae). General differ-ences between the two families are as follows:the sedges have solid stems, closed sheaths,and 3-ranked leaves, and the fruit has a seedthat is not fused to the ovary wall. The grasseshave hollow stems, open sheaths, 2-rankedleaves, and the fruit has a seed joined to theovary wall.The drooping sedge is a tufted, grasslike

perennial herb with branching, scalyrhizomes. The leaves arise from the base and

are long and slender. In the Carex inflores-cence the male flowers are borne separatelyfrom the female flowers. The terminal spikeis staminate, while the subterminal spikesare pistillate, and all these are produced onlong, drooping stalks that become progres-sively longer from top to bottom. The femaleflowers are enclosed in a saclike structure

called the perigynium. The stigmas protrudethrough the opening at the top of the peri-gynium, and as many as 130 perigynia maycomprise one flower spike in this species.

The seeds are brownish and somewhat

triangular in shape.

Turk’s-cap Lily: Lilium superbumLily Family: Liliaceae

Superbum, which means magnificent inLatin, is an appropriate name for the turk’scap, the tallest and most spectacular of ournative lilies. This species also has moreflowers than any other native lily. Theflower droops gracefully from the tip of thepetioles, revealing deep reddish orange pet-als and sepals splashed with many shades ofpurple and rust-colored anthers. The stemssometimes reach 9 feet tall.Lilium contains about 70 species widely dis-

tributed throughout the world, with theirgreatest concentration in warm temperate and

subtropical regions. The turk’s-cap grows inwet meadows and low grounds from NewBrunswick to Minnesota and south to Florida,Tennessee, and Missouri and tends to exhibita more colorful display in moist soil. It iscommon in the meadow at the Arboretum andblooms from June until August.This perennial herb has a stout, erect stem

up to 9 feet tall. The principal leaves are ar-ranged in whorls up to the inflorescence.The smooth, narrow blades are parallelveined and taper at the ends. The spectacularred-orange flowers are produced in an umbelor terminal raceme, with as many as 25flowers nodding from long pedicels. Theperianth segments are strongly recurved,with the curvature beginning below themiddle of the segment. Newly opened flow-ers may not show much curvature, but theydo so eventually, exposing the pale green

34

Drooping Sedge (Carex cnmta)

35

Turk’s-Cap Lily (Lilium superbum)

36 . "

Yellow Loosestrife (Lysimachia terrestns)

37

base and deep purple spots. The anthers arelinear and the stigma is 3-lobed. The fruit isa capsule that splits along 3 lines when ma-ture.

Many plants known as lilies do not belongto the genus Lilium and therefore are nottrue lilies. Lily of the valley belongs to Con-vallaria, day-lily to Hemerocallis, corn-lilyto Clintonia, and trout-lily, better known asdog-tooth violet, to Erythronium.

Yellow Loosestrife: Lysimachiaterrestris

Primrose Family: Primulaceae

The yellow loosestrife, or swamp candle(Lysimachia terrestris), often reproducesvegetatively by bulbels produced in suchareas on the plant as the leaf axis or theinflorescence. Linnaeus took these bulbels

to be a parasitic mistletoe species, which he

placed in the mistletoe genus, Viscum. Somepopulations of this species are quite florifer-ous and include no bulbel-bearing plants;others include bulbel-bearing plants but noflowers; and still others include plants thatexhibit both.

In North America this plant grows fromNewfoundland and Quebec southward toSouth Carolina and westward to Minnesota.At the Arboretum it is common in themeadow and along Bussey Brook, bloomingfrom late June to August.The rhizomes produce erect, simple or

branching stems up to 3 feet tall. The leaveson the lower stem are scalelike and smallerthan the opposite, sessile narrow leaves pro-duced further up the stem. The blades are

punctate with dark purplish dots and short

streaks above and somewhat whitish be-neath. The inflorescence is a raceme, termi-nal on the main stem or sometimes in theaxils of the branches. The star-shaped flow-ers, each with 5 basally united yellow petalsand single maroon eye, are borne on thread-like pedicels. The filaments are united at thebase, and the anthers are lavender-purple.The seeds are somewhat rounded with a

shiny black surface.

Soft Rush: juncus effususRush Family: Juncaceae

Juncus is the largest genus in the family Jun-caceae and includes about 225 species, mostof which occur in wetland habitats. About90 species are found within the UnitedStates and Canada, and perhaps no species ofthe genus is more familiar than is juncus ef-fusus, the soft rush. This plant is widely dis-tributed in temperate regions of both thenorthern and southern hemispheres. At theArnold Arboretum it is common in themeadow and along pond and stream mar-gins.This grasslike perennial has vigorous,

scaly rhizomes and often forms large, brightgreen tussocks up to 4 feet tall. The soft,basal leaves are quill-like, with chestnut-colored leaf sheaths that are bladeless andbristle tipped. Associated with the inflores-cence is a stiff involucral bract that is sharp-ly pointed and appears to be a continuationof the stem. The inflorescence is an openpanicle, consisting of 30 to 100 flowersborne singly on many uneven stalks. Theperianth is not differentiated into sepals andpetals but is in two series of three segments

38

Soft Rush ( Juncus effusus)

39

each. The outer whorl is keeled and theinner whorl flat. The seed capsule, lightbrown and smooth, is 3-sided and rounded atthe apices. The seeds are small with darkershort-pointed extremities.

For more than a century the soft rush hasbeen a wetland crop in Taiwan, China,Korea, and Japan, where the dried stems areused for floor matting.

Tall Meadow-Rue: Thalictrum

polygamum ’

Buttercup Family: Ranunculaceae

Tall meadow-rue (Thalictrum polygamum)is one of the most easily located plants in thefield, as its masses of soft, feathery whiteflowers rise above most other wetland

plants. This perennial herb grows to 11 feettall and can be found in wetlands, swamps,and low thickets from Newfoundland to On-

tario, south to Nova Scotia, Georgia, andTennessee. At the Arboretum it is commonin the meadow and along Bussey Brook,blooming from June through September.The stems of tall meadow-rue are light

green at first but become tinged withmagenta later in the season. The leaves are

pinnate, with 3 or more leaflets. The large,graceful, terminal panicles can be rounded orflat at the top. Some plants display purewhite flowers while others produce purplishflowers. Meadow-rue includes perfect (con-taining both stamens and pistils) and uni-sexual (containing only stamens or onlypistils) flowers on single plants. Botanistshave termed this conditionpolygamous, andthe species name polygamum refers to this.The achenes (small, dry, one-seeded fruits)are short-stalked. This species has no pet-als, so the color of the flower, which can be

white, pink, or purple, is provided by thecluster of stamens or pistils. (See inside frontcover for illustration.)

40

A Species List of Aquatic and Wet-land Plants Observed in theArboretum Since 1930

Monocotyledons (Monocotyledoneae)Plants with all or some of the following characters: vas-cular bundles distinct and scattered in the intemodes ;cotyledon, or seed leaf, solitary, flowers with parts usu-ally m 3s or multiples of 3; leaves parallel-veined;fibrous root system; plants usually herbaceous.

Alismataceae - Water-Plantain FamilyAhsma subcordatum Raf. - water-plantain p m sAhsma trmale Pursh-water-plantam p m sSagittaria latifolia Willd. - duck-potato p m s

Araceae - Arum FamilyAcorus calamus L. - sweetflag p sPeltandra mrgm~ca (L.~ Schott & Endl. - arrow-arum pSymplocarpus foetidus /L.) Nutt. - skunk cabbage m

Callitrichaceae - Water-Starwort FamilyCalhtmche heterophvlla Pursh - water-starwort p s

Cyperaceae - Sedge FamilyCarex annectens Bickn. - yellow fox sedge p sCarex blanda Dew. m

Carex canescens L. m s

Carex conoidea Schkuhr-silvery sedge mCarex cnmta Lam. - drooping sedge m sCarex debihs Michx. p m sCarex echmata Murr. mCarex hirta L. mCarex hystricma Muhl. - porcupine sedge m sCarexlanugmosa Michx. mCarex lupulma Muhl. pCarex lunda Wahlenb. - sallow sedge mCarex pallescens L.-pale sedge m sCarex pamcea L. mCarex scopana Schkukr mCarex stncta Lam. - tussock sedge mCarex stipata Muhl. - awl-fruited sedge mCarex tnbuloides Wahlenb. p m sCarex vulpmoidea Michx. mCyperus stngosus L. - straw-colored sedge p mEleochans aciculans /L.) R. & S.-least spike-rush mEleocharis calva Torr. pEleochans gemculata (L.) R. & S. pEleochans obtusa (Willd.) Schultes - blunt spike-rushpms s

p pondm meadows stream

Eleocharis ovata /Roth~ R. 8, S pEleochans palustns (L.) R. & S. p m

Rynchospora capitellata (Mtchx.) Vahl - beak rushpm

Scirpus atrocmctus Fern. mScmpus atromrens Willd. - dusky bulrush m sScirpus cypennus (L.) Kunth-wool-grass m sScirpus expansus Fern. p m sScirpus polyphyllus Vahl m

Gramineae - Grass FamilyAlopecurus gemculatus L. mAlopecurus pratensi L. - meadow-foxtarl m sAnthoxanthum odoratum L - sweet vernal grass m

Calamagrosus canadensis (M~chx.l Nutt.-blue-~omtgrass p m s

Cmna arundmacea L. -wood reedgrass p m sDactyhs glomerata L. - orchard grass mGlycena acutiflora Torr. pGlycena canadensis (Michx.) Trm. 2014 rattlesnake-

grass s

Glyceria grandis S. Wats. -- reed-meadow grass p mGlycena laxa Scnbn - northern manna-grass p mGlycena palhda (Torr I Tnn.-pale manna-grass pGlvceria stnata /Lam ~ Hitchc. - fowl-meadow grasspms s

Leersia oryzoides (L.~ Sw. - nce-cutgrass p m sLeersia mrgmica Willd - whitegrass p sMuhlenbergia schreben J. F Gmel-drop-seed grass mPhalams arundmacea L. - reed-canary grass m sPhleum pratense L - timothy mPoa compressa L. - Canada bluegrass mPoa palustris L. m sPoa pratensis L. - Kentucky bluegrass mSparuna pecunata Lmk- cord-grass s

Indaceae - Iris FamilyIns pseudacorus L. - yellow ms p m sIns versicolor L. - common blue flag p m sSisynnchmm atlanucum Bickn. m

Juncaceae- Rush Familyjuncus bufomus L - toad-rush mjuncus canadensis J. Gay mjuncus d~chotomus Ell. mjuncus effusus L. p m sjuncus margmatus Rostk. mjuncus tenms Willd. - tufted rush m

Lemnaceae - Duckweed FamilyLemna minor L. - duckweed p s

Liliaceae - Lily FamilyLihum canadense L. - Canada lily mLihum philadelphicum L.-wood-hly mLilium superbum L. - turk’s-cap lily mUvulama sessihfoha L.-mld-oats s

41

Orchidaceae - Orchid FamilyHabenana lacera (Michx.) Lodd. - ragged orchis mHabenana psycodes ~L.~ Spreng. - purple-fringed

orchis s

Spmanthes cernua (L.) Richard -nodding ladies-tressesms s

Spiranthes gracihs (Bigel.) Beck - southern slenderladies-tresses m

Spiranthes tuberosa Raf. 2014little ladies-tresses mPotamogetonaceae - Pondweed FamilyPotamogeton epihydrus Raf. - pondweed pPotamogeton fohosus Raf. - pondweed p

Spargamaceae - Bur-Reed FamilySpargamum eurycarpum Engelm. - bur-reed p

Typhaceae - Cat-tail FamilyTypha laufolia L. - broad-leaved cat-tail p m s

Dicotyledons (Dicotyledoneae)Plants with all or some of the following characters: vas-cular bundles of stem usually m a ring (sometimes scat-tered m a few aquatics); cotyledons usually 2 or rarely 1m a few aquatics; flowers with parts usually m multi-ples of 2, 5, or more; leaves pmnately or palmatelyvemed; roots usually fibrous; plants herbaceous orwoody.

Asclepladaceae - Milkweed FamilyAsclepias mcarnata L. - swamp-milkweed p s

Balsaminaceae 2014 Touch-Me-Not FamilyImpatiens capensis Meerb. - spotted touch-me-notpms s

Boraginaceae 2014 Borage FamilyMyosotis scorpiordes L. - forget-me-not s

Capnfoliaceae - Honeysuckle FamilySamrucus canadensis L - elderberry m ,

Chenopodiaceae - Goosefoot FamilyChenopodmm glaucum L. - oak-leaved goosefoot m

Compositae - Composite FamilyAsterlaems L -smooth aster mAsterlatemflorus /L.~ Britt. m sAster novi-belgii L - New England aster p m sAsterpumceus L - purple-stemmed aster m sAster simplex Willd. - tall white aster pAster mmmeus Lam. - small white aster m sBidens cernua L. - stick-tight p m sBidens connata Muhl - beggar-ticks p m sBidens frondosa L. - beggar-ticks p m sBidens vulgata Greene - beggar-ticks p m s

Eupatonum dubmm Willd. - Joe-pye-weed pEupatonum perfohatum L.-thoroughwort mSohdago canadensis L. - Canadian goldenrod m sTanacetum vulgare L. - tansy p m s

Convolvulaceae - Convolvulus FamilyConvolvulus sepmm L.-hedge bmdweed mCuscuta gronovm Willd. - common dodder m s

Cuscuta pentagona Engelm. s

Cruciferae - Mustard FamilyBarbarea vulgans R. Br. -yellow rocket m sDiplotaxis murahs /L.) DC. - sand rocket pRonppa nasturtium-aquaticum /L.~ Bntten & Rendl.

(Nasturium officmale R. Br.) p sRonppa palustns /L.) - Bess-marsh cress p m

Euphorbiaceae - Spurge Family yAcalypha mrgmica L. - three-seeded mercury m

Gentianaceae - Gentian FamilyGentiana cnmta Froel. -fnnged gentian mHypericum boreale /Bntt.) Bickn. pHypencum canadense L. m

’

Hypencum mo~us (Gray) Bntt. mHypemcum mutilum L. - slender St. John’s-wort p m s

Labiatae - Mmt FamilyLycopus amencanus Muhl. - cut-leaved water-horehound p m s

Lycopus umflorus Michx. - water-horehound p m sLycopus vmgmicus L. - water-horehound sMentha arvensis L. - field mmt p m sPrunella vulgans L. - selfheal mScutellana latenflora L. - mad-dog skullcap m

Lentibularlaceae - Bladderwort FamilyUtmculana vulgans L - common bladderwort pLobehaceae - Lobelia FamilyLobeho cardmahs L. - cardmal flower pLobeha siphihtica L - great blue lobeha m s

Lythraceae - Loosestnfe FamilyDecodon verticillatus (L./ Ell. - swamp loosestrife pLythrum sahcana L. -purple loosestnfe p m s

Malvaceae - Mallow FamilyMalva moschata L. musk-mallow p

Nymphaeaceae - Water-Lily FamilyNymphaea odorata Ait. - fragrant water-lily p

Onagraceae - Evemng-Pnmrose FamilyEpilobmm coloratum Biehler-purple-stemmed

willow-herb m s

Ludwigia palustns (L.) Ell. - water-purslane pOenothera bienms L. - common evening pnmrose mOenothera perenms L. - sundrops p m

42

Polygonaceae - Buckwheat FamilyPolygonum omphibmm L. - water-smartweed pPolygonum anfollum L. - halberd-leaved tearthumbpm

Polygonum aviculare L. - knotweed mPolygonum coccmeum Muhl. - swamp smartweedpms s

Polygonum hydropiper L. - water-pepper p m sPolygonum hydropiperoides Michx. - mild water-

pepper p m

Polygonum lapathifohum L. pPolygonum punctatum Ell. - water-smartweed mPolygonum sagittatum L. - arrow-leaved tearthumbpm

Rumex obtusi fohus L. - bitter dock m

Pontedenaceae - Pickerelweed FamilyPontedena cordata L. -pickerelweed pPnmulaceae - Pnmrose FamilyHottoma mflata Ell. - featherfoll pLysimachia quadnfoha L. - whorled loosestrife mLysimachia terrestns (L.) BSP. - yellow loosestrife m

Ranunculaceae - Buttercup FamilyRanunculus acns L.-tall buttercup mRanunculus repens L. - creeping buttercup m sThahctrum polygamum Muhl. - tall meadow-rue m s

Rosaceae - Rose FamilyRubus hispidus L. - dewberry m

Rubiaceae - Madder FamilyGahum palustre L. - marsh bedstraw mGallum tmctomum L. - marsh bedstraw m

Saxifragaceae - Saxifrage FamilyPenthorum sedoides L. - ditch-stonecrop m

Scrophulanaceae - Figwort FamilyAgahms paupercula (Gray) Pennell- small gerardiams s

Agahms tenmfoha /Vahl.) Raf.-slendergerardia m sChelone glabra L. - turtlehead p m sLmderma dubia /L.~ Pennell - false pimpernel p mMimulus nngens L. - monkey-flower m sVeromca of~cmahs L.-common speedwell mVeromca scutellata L. - marsh speedwell pSolanaceae- Nightshade FamilySolanum dulcamara L. - bittersweet nightshade s

Trapaceae - Water-Chestnut FamilyTrapa natans L. - water-chestnut p

Umbelhferae - Parsley Family -

Cicuta bulbifera L. - water hemlock p sCicuta maculata L. - spotted cowbane p m sHydrocotyle amencana L. - water pennywort m

Smm suave Walt. - water-parsmp p m s

Urticaceae - Nettle FamilyPilea pumila (L.) Gray - clearweed m

Verbenaceae - Vervain FamilyVerbena hastata L - blue vervain m

Violaceae - Violet FamilyViola cucullata Ait. - marsh blue violet mViola lanceolata L. -lance-leaved violet p m sViola pallens (Banks) - brainerd-sweet white violetms s

Viola papilionacea Pursh- common blue violet m

Pteridophytes (Pteriodophyta)Plants that are fernlike, rushlike, mosslike, or quill-leaved and have no seeds or flowers but reproduce byspores.

Eqmsetaceae - Horsetail FamilyEqmsetum arvense L. - field horsetail pEquisetum fluviatile L. - water horsetail pEqmsetum sylvaticum L. m

Lycopodiaceae - Club Moss FamilyLycopodium complanatum L. - trailing ground-pinems s

Marsileaceae - Pepperwort FamilyMarsilea quadmfoha L. - pepperwort p

Osmundaceae - Flowering Fern FamilyOsmunda cinnamomea L. - cinnamon-fem sOsmunda claytomana L. - mterrupted fern m sOsmunda regahs L. - royal fem m s

Polypodiaceae - Fern FamilyOnoclea sensibihs L. - sensitive fern p m s

Dryoptens thelyptens (L.) Gray - marsh shield fem m

I

43

References

Adams, P., and R. K. Godfrey. 1961. Observations cf theSagittana subulata complex. Rhodora 63: 247-266.

Anderson, E. 1928. The problem of species m the north-em blue-flags Ins versicolor L. Annals of theMissouri Botanical Garden 15: 24-332.. 1936.The species problem m Ins. Annals of the

Missouri Botamcal Garden 23: 457-509

Blackwell, W. H., Jr., 1972. The combmarionPeltandzavirginica (L.) Schott & Endlicher. Rhodora 74:516-518.

Bogm, C. 1955. Revision of the genus Sagittana (Alis-mataceae). Memoirs of the New York BotanicalGarden 9: 179-233.

Cody, W. J. 1961. Ins pseudacorus L. escaped from cul-tivation m Canada. The Canadian FieldNaturahst 75: 139-142.

Conrad, M. S. 1905. The Water Lihes~ A Monograph ofthe Genus Nymphaea. Pubhcation of the Car-negie Institution Waslvngton 4: 1-279

Cook, C. D. K., B. J. Gut, E. M. Rix, J. Schneller, andM. Seitz. 1974. Water Plants of the World. Dr.W. Junk b.v., Pubhshers, The Hague.

Crocker, W. 1907. Germination of seeds of water plants.Botanical Gazette 44: 375-380.

Crocker, W., and W. E. Davis. 1914. Delayed germina-tion in seed of Ahsma plantago. BotamcalGazette 58: 285-321.

Eaton, R. J. 1947. Lemna mmor as an aggressive weed mthe Sudbury Rmer. Rhodora 49~ 165-171.

Fassett, N. C. 1957. A Manual of Aquauc Plants. Um-versity of Wisconsm Press, Madison, Wisconsm.

Fassett, N. C., and B. Calhoun. 1952. Introgression be-tween Typha lattfoha and Typha angusufoha.Evolution 6: 367-379.

Fernald, M. L. 1970. Gray’s Manual of Botany, 8th edi-tion. D. Van Nostrand Company, New York.

Fernald, M. L., and K. M Wiegand. 1910. The NorthAmencan variations of {uncus effusus. Rhodora12: 81-93.. 1905. The hybnd of Lysimachia terrestns and

Lysimachia thyzsiflora. Rhodora 52: 199-201.Gleason, H. A. 1952. The New Bntton and Brown Illus-

trated Flora of the Umted States and Ad~acentCanada Lancaster Press, Lancaster, Pennsyl-vania.

Godfrey, R. K., and J. W. Wooten. 1979. Aquatic andWetland Plants of the Southeastern UmtedStates. The University of Georgia Press, Athens,Georgia.

Graham, S. A. 1964. The genera of Lythraceae in the

southeastern United States. Journal of the Ar-nold Arboretum 45: 235-250.

Gupta, K. M. 1957. Some species of Marsilea with spe-cial reference to their epidermal and soral charac-ters. Madrono 14: 113-127.

Hendricks, A. J. 1957. A revision of the genus Alisma(Dill.) L. Amencan Midland Naturahst 52: 470-493.

Hicks, L. E. 1932. Flower production m the Lemnaceae.Ohio Journal of Science 32: 115-131.

Hotchkiss, N., and H. L. Dozier. 1949. Taxonomy anddistribution of North Amencan cat-tails. Amer-ican Midland Natuzahst 41: 237-254.

Knutson, R. M. 1979. Plants m heat. Natural History88/3/: 42-47.

Koehne, E. 1885. The Lythraceae of the United States.Botanical Gazette 10(5): 269-277.

Lawrence, G. N. M. 1951. Taxonomy of VascularPlants. Macmillan, New York.

Li, Hui-Lm. 1955. Classification and phylogeny ofNymphaceae and allied families. American Mid-land Naturahst 54: 33~1.

Lowden, R. M. 1973. Revision of the genusPontedena.Rhodora 75: 426-487.

Mahabale, T. S. 1972. Water fems: Their origin andspread. Birbal Sahm, Institute of PalaeobotanyLucknow, Poona, India.

Palmer, E. J. 1930. The spontaneous flora of the ArnoldArboretum. Journal of the Arnold Arboretum 11:63-119.. 1935. Supplement to the spontaneous flora of

the Arnold Arboretum. Journal of the Arnold Ar-boretum 16: 81-97.

Ad Hoc Panel of the Advisory Committee on Technol-ogy Innovation, Board on Science and Technol-ogy for International Development, Commissionon International Relations. 1976. Making Aquat-ic Weeds Useful.~ Some Perspectmes for Devel-oping Countries. National Academy of Sciences,Washington, D.C.

Rossbach, G. B. 1939. Aquatic Utmculanas. Rhodora41: 113-128.

Saeger, A. 1929. The flowering of Lemnaceae. Bulletmof the Torrey Botanical Club. 56: 351-358.

Schrenk, J. 1889. On the floating tissue of Nesaea ver-ticillata (L.) MBK. Bulleun of the TorreyBotam-cal Club 16: 315-23.

Skitch, A. F. 1928. The capture of prey by the bladder-wort : a review of the physiology of bladders. NewPhytologist 27’ 261-97.

Slack, A. 1980. Cazmvozous Plants. Massachusetts In-stitute of Technology Press, Cambndge, Massa-chusetts.

44

Small, J. K. 1931. The water lilies of the Umted States.Journal of the New York Botamc Garden 32:117-121.

Smith, S. G. 1967. Experimental and Natural Hybrids mNorth Amencan Typha (Typhaceae). AmericanMidland Naturalist 78: 257-87.

Stason, M. 1926. The Marsileas of the western UmtedStates. Bulletm of the Torrey Botamcal Club 53:473-78.

Stuckey, R. L. 1980. Distributional history of Lythrumsahcana (purple loosestrife) in North America.Bartoma 47: 3-20.

Tomlinson, P. B. 1982. Helobiae /Alismatidae~. Vol. 7 inAnatomy of the Monocotyledons, C. R. Metcalfe,ed. Clarendon Press, Oxford.

West, D., and D. F. Whigham. 1976. Seed germination ofarrow-arum (Peltandra vmgmica L.). Bartoma 44:44-49.

Wood, C. E. 1959. The genera of the Nymphaeaceae andCeratophyllaceae m the southeastern UmtedStates. Journal of the Arnold Arboretum 40~ 94-112.

Wooten, J. W. 1973. Taxonomy of seven species ofSagittana from eastern North Amenca. Bartoma

~

25: 64-74.

Patncia A. Dalton is the author of Wildflowers of theNortheast m the Audubon Fairchild Garden (AudubonCenter in GreenmchJ. She has been updatmg the rec-ords of the Immg collections at the Arnold Arboretumduring the past two years.

Ale~andro Novelo R. is a taxonomist speciahzmg maquatic plants at the Umversidad Nacional Autonoma ,

de Mexico in Mexico City.

Amy Storey is an artist and botamcalillustratorlmngin Victoria, Bmush Columbia.