Evolution of Land Plants Artist’s rendering of Carboniferous forest in a tropical river delta....

Evolution of Land Plants

Artist’s rendering of Carboniferous forest in a tropical river delta. Most of the plants depicted here were nonseed tracheophytes 10 to 20 meters tall. In the distance, early seed plants up to 40 meters tall towered over the forest.

Prior to the origin and diversitication of green plants in the mid-Silurian (~450 mya), multicellular life was virtually entirely adapted to, and confined to, aquatic lifestyles

Continental land Masses virtually unoccupied by multicellular organism – multicellular-based ecosystems constituted tremendous potential for adaptive radiation

Terrestrial life in a gaseous medium required evolutionary solutions to structural, physiological and ecological challenges; Many of these innovations can be regarded as exaptations of pre-existing traits of green algae from which green plants diverged

Sources: Freeman (2002), Purves et al (2001)

Kingdom Plantae is monophyletic assemblage, descended from Green algae

Chlorophyll a and b are homogous in Chlorophyta, Charaphyta and Plantae

Currently includes over 250,000 described species classified in 12 monophyletic phyla

Most are terrestrial, some are secondarily aquatic

Diversification in plants involved successive adaptive radiations following evolution of key innovations that increased efficiency in a gaseous (air) and solid (Earth) environment

Major problems were posed by gravity and by water loss/availability

-maintain body structure in air (and with increasing body size) – resist gravity-obtain, transport and retain water-fertilize eggs and produce and protect embryos

Major evolutionary innovations included

-dimorphic body-waxy cuticle and stomata- true vascular tissue; -life history dominated by sporophyte generation -jacketed sex organs; antheridia and -archegonia-seeds; embryo with nutritive tissue in protective covering-flowers; vehicles for pollination strategies

Green algae of the lineage that includes Chara sp., are most likely ancestors of plants. Copyright BPS.

Ie, “true” vasular tissue



First extensive grassland

First Flowering Plant

First nectar-drinking insects

First vessels

1st seeds1st vascular plant leaves1st wood1st roots1st vascular tissue1st stomata

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1st megafossils (small club mosses and other extinct groups 1st lycopod leave

1st evidence of land plants


A primer on terminology associated with vascular tissue

Vascular tissue; tissue involved in transport of materials (water, minerals…) in plants -- we’re focusing on water transport in this discussion

Tracheids specialized cells for water transport; first “true” vascular cells.

Tracheophytes are plants with Tracheids

Mosses have cells that have a vascular function, hence its not entirely correct to refer to them as “nonvascular”, but they are definitely “non-tracheophyes”, as are liverworts and hornworts

Tracheophytes have two vascular tissue types, each composed of several cell types

xylem; transports water and dissolved minerals; cell types are tracheids and, in flowering plants, vessel elements

phloem; transports sugars, ie, products of photosynthesis; minerals too; sieve-tube members and companion cells

Mature vessel elements in Zea mays; open perforation plate allows vessel to act as a water pipe. SEM. Copyright John N. A. Lott/BPS.

tracheids Vessel elements


A primer on reproductive cells, embryos, seeds, and life cycles

Alternation of generations occurs in all plant life cycles, but not all Charorphyceans; this trait evolved independently as a derived characteristic of land plants

In some algae with alternation of generations, sporophytes and gametophytes look similar; not so in land plants – in all species sporophytes and gametophytes are very different morphologically

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Marchantia, a common liverwort. The sporophytes are born within the tissues of the umbrella shaped structures that arise from the surface of the flat, green, creeping gametophyte

A primer on reproductive cells, embryos, seeds, and life cycles

spores are 1n cells that can divide mitotically, with no syngamy, to produce individuals

gametes are 1n cells that undergo syngamy to produce a (2n) multicellular individual

embryo embryonic plant that develop from zygotes within tissues of the female parent (which provides nutrients)

seed Unique structure in “seed plants”; key structure in domination of terrestrial habitats by plants; plant embryo and its food supply, packaged in a protective coat. gymosperms (conifers and their relatives) produce “naked” seeds in that they are not born in protective chambers. angiosperms produce seeds

alternation of generations

Embryo of Marchantia, a liverwort

Embryo of shepherd’s purse an angiosperm

Three ways of expressing (the same!!) phylogenetic relationships among major plant lineages

Cladogram to the left is particularly useful in that it shows:

-extinct non-seed tracheophyte lineage Rhyniopsida

-origin of important innovations, including independent origins --homoplasies


Rhynie in the Grampian Region of Scotland has become famous as one of the most important palaeobotanical localities in the world. In 1912 the Scottish geologist William Mackie discovered an occurrence of Lower Devonian plant-bearing cherts near this small village. Recent radiometric datings of these rocks give an age of396 ± 12 million years

Rhynie Chert cut perpendicularly to the stratification showing successive horizons

Nature 389, 33 - 39 (1997) © Macmillan Publishers Ltd.

The origin and early evolution of plants on land

PAUL KENRICK AND PETER R. CRANE

the Swedish Museum of Natural History, Box 50007, S-10405, Stockholm, SwedenThe Field Museum, Roosevelt Road at Lake Shore Drive,

Chicago, Illinois60605, Department of the Geophysical Sciences, University of Chicago, USA.

The origin and early evolution of land plants in the mid-Palaeozoic era, between about 480 and 360 million years ago, was an important event in the history of life, with far-reaching consequences for the evolution of terrestrial organisms and global environments. A recent surge of interest, catalysed by palaeobotanical discoveries and advances in the systematics of living plants, provides a revised perspective on the evolution of early land plants and suggests new directions for future research.

Our current understanding of Plant phylogenetic relationships is based on analysis of both morphological and molecular characters

•SSU rRNA and Rubisco

•presence/absence of vascular tissue, leaves, seeds…

The broad picture of plant macroevolutionary patterns includes…

•Divergenge of entire clade from green algae

•All Plantae lineages; cellulose-based cell walls, chlorophyll a and b, starch as storage molecule in chloroplasts

•Two of the three earliest lineages (non-tracheophytes) lack water transport cells; mosses have have limited numbers of them

•Seedless vascular plants (nonseed tracheophytes) have vascular tissue and leaves, but reproduce by making spores; no seeds

Gymnosperms and Angiosperms have vascular tissue, they have complex leaves, and they produce seeds.

Early lineages dependent on wet habitats and more recent ones not – adaptive radiations into mesic and xeric conditions

Rubisco catalyzes a reaction in the Calvin-Benson cycle of photosynthesis in which carbon from CO2 is added to a five-carbon chain.

Leafy liverwort (Lophocolea bidentata), showing overlapping leaves and creeping growth form. Copyright BPS.

Gametophytes of Sphagnum moss growing in a bog in central Newfoundland. Copyright BPS.

Leafy liverwort (Lophocolea bidentata), showing overlapping leaves andcreeping growth form. Copyright BPS.

Dense matt of mosses colonizes old lava in Iceland. Copyright BPS

Marchantia, a common liverwort. The sporophytes are born within the tissues of the umbrella shaped structures that arise from the surface of the flat, green, creeping gametophyte

Hornwort sporophytes. Unlike other Bryophytes, hornwort sporophytes are photosynthetic

Club Moss Big leaf maples hung with epiphytes, most of which are club mosses; Hoh Rain Forest, WA. Copyright BPS.

Order Lycopodiales: club moss (Lycopodium annotinum); Denali National Park and Preserve, AK. Copyright BPS.

Fern (Blechnum magellanicum) in rain forest of Chile's Patagonian coast. Copyright Alejandro Frid/BPS.

Tree ferns (Dicksonia antarctica), in a forest of Eucalyptus regnans; Australia. Copyright BPS.

Family Pinaceae: Pinus ponderosa, ponderosa pine, is widespread in the American West. Copyright BPS.

Family Pinaceae: Colorado blue spruce (Picea pungens). Copyright Pollock/BPS.

Simple determinate inflorescence of shooting star (Dodecatheon meadia). Copyright J. Robert Stottlemyer/BPS.

Family Arecaceae: desert fan palm (Washingtonia filifera); Colorado Desert, CA. Copyright Jon Mark Stewart/BPS.





First vessels

1st megafossils (small club mosses and other extinct groups and 1st lycopod leave


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The Transition to Land involved evolution of three important steps

Preventing cell dessication

Transporting water from cells in plant body with direct access to water, to cells without

Transporting gametes by a mechanism other than floating or swimming in water

The earliest interval of plant evolution on our time scale has yielded fosils of:

-spores surrounded by tough membrane made of sporopollenin-sheets of a waxy material – cuticle-small tubes

fossilized spores in tetrads





First vessels

1st megafossils (small club mosses and other extinct groups

1st lycopod leave


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Leaf epiderm of dayflower (Commelina sp.), a monocot. LM. Copyright Alfred Owczarzak/BPS.

Stomata in leaf of corn, a monocot. Copyright John N. A. Lott/BPS

Cross-section of a modern leaf (eudicot)

Waxy cuticle solved one problem and caused another – it impeded uptake of carbon dioxide

modern plants have specialized cells that solve this problem; two specialized guard cells form a stoma (pore) that can be open or closed.

Stomata occur in some extant basal lineages -- hornworts and mosses

Stomata are known from 385 million years ago, from a fossil Rhyniopsid





First vessels


1st lycopod leave


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Stomata in leaf of corn, a monocot. Copyright John N. A. Lott/BPS

Early Devonian rhyniophyte fossils. f. Stomate with tworeniform guard cells (stippled

Key evolutionary innovations solved the problems of structural support and internal water transport

First land plants probably were low, sprawling

before evolution of rigid body support, algal-like tissue could not grow erect, resist gravity

Before evolution of internal water transport system, virtually entire plant had to communicate directly with water

Among communities of low, sprawling plant – growing horizontally in a sense, competition for space and light was probably intense –intense selection for erect growth forms

Transition to terrestrial life required

-internal water transport to high and dry parts of plant, against the force of gravity

-rigidity of body in order to resist forces of gravity and wind

Dense matt of mosses colonizes old lava in Iceland may be remniscent of early plant life forms – low and sprawling. Copyright BPS

Artist’s rendering of Carboniferous forest in a tropical river delta. Most of the plants depicted here were nonseed tracheophytes 10 to 20 meters tall. In the distance, earl seed plants up to 40 meters tall towered over the forest.





First vessels


1st lycopod leave


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Water-conducting xylem vessels in a cucumber. LM. Copyright J. Robert Waaland/BPS.

Mature vessel elements in Zea mays; open perforation plate allows vessel to act as a water pipe. SEM. Copyright John N. A. Lott/BPS.

Cross section of vascular bundles from a eudicot stem; nutrient-conducting phloem, water-conducting xylem. LM. Copyright James Solliday/BPS.

Modern day tracheids (left) and vessel elements (right)

Water transport and structural support

Rhynie chert (~400 mya) bears fossil plants in an erect, upright postion – fossils suggest many or most plants grew erect

Kenrick and Crane identifed four types of water-conducting cells in the Rhynie chert (not tracheids or vessel elements) – some with lignified rings that may have allowed plants to assume an upright life form (lignin; strong, lightweight 6-carbon polymer

By about 380 mya, fossil record bears tracheids; advanced water conducting cells found in all modern phyla of vascular plants. Later tracheids with extensive lignification and thickened secondary walls

Wood develops from “secondary xylem”, and arose independently in several lineages by about 380 mya. First trees appear in fossil record some 370 mya





First vessels


1st lycopod leave


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tracheids

vessels

pits

top; picture of some of the first tracheids 380 mya from the fossil record; diagram shows tracheids from modern plantbottom; photo of 50 my old vessels and diagram of modern vessels. Vessels are shorter and fatter than tracheids, and stacked end to end. Water flows up vessels directly, and laterally, from vessel to vessl, as well, through perforations in primary and secondary cell walls

above water-conducting cells from rhynie chert

Evolution of heterospory and male and female gametophytes

The earliest tracheophytes were homosporous.

Heterospory evolved multiple times in tracheophytes in early evolution of land plants (occurs in Rhyniophyte lineage)

Multiple evolutionary origins suggests heterospory affords selective advantages;

Later tracheophytes, especially seed plants, show ever greater specialiation of the heterosporous condition Homosporous plants have a single type of

spore that gives rise to a single type of gametophyte, which bears two types of sex organs

Heterosporous plants have two types of spores, each of which develops into male or female gametophytes, each of which produces eggs or sperm




First vessels

1st megafossils (small club mosses and other extinct groups and 1st lycopod leaves


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Protecting and transporting Embryos: Evolution of seed and pollination

All land plants have life cycles with alternation of generations.

Relationship between gametophyte and sporophyte varies among lineages in terms of size, dependence, dominance in life cycle

Mosses: sporophyte is small and depends on gametophyte for nutrition

Ferns; sporophyte is larger than gametophyte and is autotrophic (photosynthesizes its own food)

Seed plants (gymnosperms and angiosperms); sporophyte is dominant;

-male gametophyte is reduced to pollen grain-female gametophyte to a small structure that holds the egg or eggs

Gametophytes (green) of the star moss produce non-photosynthetic stalked sporophytes with caplike sporangia at their tips (Campbell 2002)




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Protecting and transporting Embryos: Evolution of pollen, pollination and seed and seed dispersal

Seed plants (gymnosperms and angiosperms); sporophyte is dominant;

-male gametophyte is reduced to pollen grain

-female gametophyte to a small structure that holds the egg or eggs

Selection favored male gametophytes highly reduced in size and encased in sporopollenin; pollen grains are the consequence of that bout of mutation and selection

Pollen grains survive for prolonged periods in dry environments without becoming dessicated

Pollen grains can be transported by wind, gravity or animals; through pollen grains, seed plants lost dependence on water for fertilization

Pollination. Carrion plant (left) has foul odor that attracts carrion flies. Hummingbird pollinated flower (middle) produces nectar. Many arge, complex flowers (eg sunflower, right) attract a host of species that act as pollinators




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Evolution of seeds and flowers

Seeds enclose and protects embryo, and has a stockpile of nutrients

Seeds are often attached to a structure that facilitates dispersal by wind, water or animals

dispersal by water

dispersal by animals

dispersal by wind

Extra slides



Archaefructus, an early flower


Cones from Araucaria mirabilis, an early gymnsperm


First vessels


1st lycopod leave


Seed fern leaves

Fragment of plant cuticle

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Cells in fossil stem of Rhynia major (extinct Phylum Rhyniophyta); late Silurian and Devonian. LM. Copyright Phil

Gates/BPS.

Spores in fossil Rhynia major; late Silurian and Devonian. LM. Copyright Phil Gates/BPS

Fossil stem of oldest known lycopod genus (Bothrodendron minutifolium); late Devonian. LM. Copyright Phil Gates/BPS.

Fossil frond of fern (Asterotheca arborescens); late Carboniferous. Copyright Barbara J. Miller/BPS.

Overview of the evolutionary history of plants

Consider five intervals of evolutionary history, each defined by at least one major evolutionary innovation

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Key Evolutionary Innovations and Trends in the Transition of Plants to Land

-reducing water loss; cuticle and stomata

-transporting water; vascular tissue and wood

-transporting gametes and prtoecting embryos; pollination mechanisms and nutrititive, protective seeds

Key evolutionary innovations and trends for capturing energy from sunlight

-Photosynthetic Pathways C3 and C4

-Crassulacean acid metabolism

-growth habits and life forms

Minimizing water loss and regulating gas exchange

Nature 389, 33 - 39 (1997) © Macmillan Publishers Ltd.

The origin and early evolution of plants on land

PAUL KENRICK AND PETER R. CRANE

the Swedish Museum of Natural History, Box 50007, S-10405, Stockholm, SwedenThe Field Museum, Roosevelt Road at Lake Shore Drive,

Chicago, Illinois60605, Department of the Geophysical Sciences, University of Chicago, USA.

The origin and early evolution of land plants in the mid-Palaeozoic era, between about 480 and 360

million years ago, was an important event in the history of life, with far-reaching consequences for

the evolution of terrestrial organisms and global environments. A recent surge of interest, catalysed

by palaeobotanical discoveries and advances in the systematics of living plants, provides a revised

perspective on the evolution of early land plants and suggests new directions for future research.

Figure 1 Morphological diversity among basal living land plants and potential land-plant sister groups. a,Coleochaete orbicularis (Charophyceae) gametophyte; magnification × 75 (photograph courtesy of L. E.Graham). b, Chara (Charophyoceae) gametophyte; magnification × 1.5 (photograph courtesy of M.Feist). c, Riccia (liverwort) gametophyte showing sporangia (black) embedded in the thallus; magnification× 5 (photograph courtesy of A. N. Drinnan). d, Anthoceros (hornwort) gametophyte showing nbranchedsporophytes; magnification × 2.5 (photograph courtesy of A. N. Drinnan). e, Mnium (moss) gametophyteshowing unbranched sporophytes with terminal sporangia (capsule); magnification × 4.5 (photographcourtesy of W. Burger). f, Huperzia (clubmoss) sporophyte with leaves showing sessile yellow sporangia;magnification × 0.8. g, Dicranopteris (fern) sporophyte showing leaves with circinate vernation;magnification × 0.08. h, Psilotum (whisk fern) sporophyte with reduced leaves and spherical synangia(three fused sporangia); magnification × 0.4. i, Equisetum (horsetail) sporophyte with whorled branches,reduced leaves, and a terminal cone; magnification × 0.4. j, Cycas (seed plant) sporophyte showing leavesand terminal cone with seeds; magnification × 0.05 (photograph courtesy of W. Burger).

Figure 2 a, Longitudinal section of part of a silicified early fossil gametophyte (Kidstonophyton discoides

from the Rhynie Chert). Antheridia (male sexual organs) are located on the upper surface of the branch;

magnification × 3.4. b, Longitudinal section of antheridium of Lyonophyton rhyniensis from the Rhynie

Chert; magnification × 40. c, Longitudinal section of archegonium (female sexual organ) of Langiophyton

mackiei from the Rhynie Chert; magnification × 80. a–c are from the Remy Collection (slides 200, 90 and

330), Abteilung Paläobotanik, Westfälische Wilhelms-Universität, Münster, Germany (photographs

courtesy of H. Hass and H. Kerp). d, Scanning electron micrograph of Tetrahedraletes medinensis

showing a spore tetrad of possible liverwort affinity from the Late Ordovician (photograph courtesy of W.

A. Taylor); magnification × 670.

Figure 3 Sporophyte diversity in Early Devonian rhyniophyte fossils. a, Cooksonia pertoniiapiculispora: sporophyte (incomplete proximally) with terminal sporangium15; magnification × 15. b,Tortilicaulis offaeus: sporophyte (incomplete proximally) with terminal sporangium81; magnification × 40.c. Tortilicaulis offaeus: sporophyte (incomplete proximally) with terminal bifurcating sporangium81;magnification × 30. d, Transverse section of sporangium showing thick wall and central spore mass;magnification × 70. e, Details of epidermis at rim of sporangium; magnification × 45. f, Stomate with tworeniform guard cells (stippled); magnification × 120.

Figure 5 Diversity of water-conducting cells (tracheids) in early land plants (median longitudinal sectionthrough cells, basal and proximal end wa. lls not shown; cells are 20–40 m diameter). a, Top,bryophyte hydroid; bottom, details of hydroid wall showing distribution of plasmodesmata-derivedmicropores (10–50 nm diameter; stipple)84. b, Top, S-type tracheid (fossil) of Rhyniopsida; bottom,details of S-type cell wall showing distribution of plasmodesmata-derived micropores (stipple) and'spongy' interior to thickenings19. c, Top, G-type tracheid (fossil) of basal extinct eutracheophytes, whichclosely resemble the tracheids of some living vascular plants; bottom, details of G-type cell wall showingpores distributed between thickenings19. d, Top, scalariform pitted P-type tracheid (fossil) typical oftrimerophyte grade plants (euphyllophytes); bottom, details of P-type cell wall showing pit chambers andsheet with pores that extends over pit apertures26.

Evolution of Land Plants Artist’s rendering of Carboniferous forest in a tropical river delta....

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Transcript of Evolution of Land Plants Artist’s rendering of Carboniferous forest in a tropical river delta....