Natural History of the Strangest Plants in the

World

Natural History of the Strangest Plants in the

World

August 2003Hydnora africana, Karasburg District, Namibia

Lytton John Musselman

Old Dominion University

Lytton John Musselman

Old Dominion University

Features of the family

Phylogeny of the family

Taxonomy

Floral biology

Diaspore

Features of the family

Phylogeny of the family

Taxonomy

Floral biology

Diaspore

Introducing the Hydnoraceae

Features of the Hydnoraceae

• No leaves or scales (unique among angiosperms)

• Subterranean holoparasites of semi-arid regions

• Relatively host specific

• Monocolpate pollen

Habit of Hydnoraceae

Succulent herbsAchlorophyllousObligate parasites

Systematic position of the Hydnoraceae has long

been debated due to extrememorphologial reduction.

Molecular data place Hydnoraceae with Aristolochiaceae

“Palaeoherbs”

Taxonomy

Only two genera comprisethe Hydnoraceae:

Hydnora and Prosopanche.

Hydnora-African

• H. johannis (=H. abyssinica)-widespread across Africa.

• H. africana-Restricted to southern Africa.

• H. triceps-found only in a small area along the Orange River in South Africa/Namibia.

• H. esculenta-Madagascar, a poorly known species.

• H. sinandevu-Kenya and Tanzania, described in 2002.

Hydnora-African

Prosopanche-New World

• P. americana -widespread on species of Prosopis (Fabaceae).

• P. bonacinae-Diversity of hosts.

Prosopanche-New World

Hydnora-Old World

Predicted distribution ofGondwanaland paleoherbs

Prosopanche

Prosopanche americana, Cordoba Province, Argentina

Hydnoraceae flowers are chamber flowers

A chamber is present abovethe stigma.

Chamber

Prosopanche americana

What is the function ofthe chamber?

Chamber

Prosopanche americana

For the insect--It provides a place for theinsect visitor to spend thenight. Mating often takes

place. Chamber

Prosopanche americana

For the plant--It provides a “holding room”

while the flower changessex.

Chamber

Prosopanche americana

Androecium

Gland

Stigma

Flower structure of Prosopancheamericana

Prosopanche americana

Prosopanche americana

Prosopanche americana

Pistillate phaseDay one

Prosopanche americana

Staminate phaseDay two

Prosopanche flowers aredichogamous, that is, have

distinctly staminate (male) andpistillate (female) phases.

Prosopanche americana

Pollinated by a nitulid (Neopocadius nitiduloides)

Oxycorynus spp. (weevils) lay eggs in flowers but are not pollinators

Life history of Prosopanche americana

Male phase

Female phase

Fruit

Host: Prosopis alba

Hydnora

Hydnora johannisAcacia spp. (Fabaceae)Beetles

Hydnora africanaEuphorbia spp.Beetles Hydnora

esculenta??????Hydnora triceps

Euphorbia dregeana???

Floral Syndromes and Hosts

OsmophoresHydnora africana-osmophores are elongate

Hydnora abyssinca-osmophores are tips of perianth

Hydnora triceps-osmophores arein folds of perianth

Oldest flowers on left

Is the osmophore in H. johannisunique?

Mature flower

Immature flower

Recent research on Hydnora triceps

Namaqualand

Namaqualand

Center of diamond dredging,

Port Nolloth

diamond smuggling….andHydnora diversity.

Succulent Karoo

• This biome is characterized by low but reliable rainfall (20-290 mm year), chiefly in the winter. It has the highest species richness for any semiarid vegetation and a high rate of endemism, exceeding 50% (Milton et al., 1997). The dominant plants in the sandy soil of these low hills are shrubby species of Euphorbia.

Rainy season, September 2001

Succulent Karoo near Port Nolloth, South Africa

Euphorbia dregeana,host of H. triceps

Dry Season, December 2002Dry Season, December 2002

Distribution of Hydnora africana is related to that of its common host, Euphorbia gregariaAssumption: true for other species as well.

History of Discovery

• Hydnora triceps first described by Drège in 1833 from material collected near Okiep in Namaqualand. Only ten specimens extant, all from the Okiep region.

• Last seen in 1888.

History of Discovery

• Johann Visser rediscovered H. triceps in 1988. Died shortly thereafter

• Eight populations located 1999-2001 in South Africa, near Port Nolloth.

• Discovered in Namibia in September 2001.

Namibia

South Africa

Previously known collections of H. triceps at red arrow

Rosh Pinnah--First Namibian collection

Orange River

Is the distribution of the parasite dependent uponthe host?

Hydnora triceps found only on E. dregeana

The sole evidence of Hydnora triceps

??

Hydnora triceps flowers underground!!

Hydnora triceps is the only known dicot with underground flowers!

Hypogeous floweringknown in only two genera

Rhizanthella gardneri Rogers, endemic to

Southwest Australia.

Hydnora triceps.

Hydnora triceps is dichogamous, that is, flowers are functionally pistillate the first day and functionally staminate

the second.

Stages in Development

Arrows indicate anthesis. Flowers to right are pistillate.

Stages in Development

Opening to chamber is openon day one

Day one

Stages in Development

Opening to chamber closes on day two

Opening to chamber is openon day one

Day two

Day one

Fruits previously unknown.

Fruits ofHydnoratriceps

Fruits hollowed out by unknown animal.

Hypogeous

floweringand fruiting known

only in H. triceps

Day one

Hydnora africana

Day oneDay two

Day one-PistillateDay two-Staminate

Day one

Day twoDay two plus

Closedantheral

ring.

Floral visitors can be trappedin flowers when ring closes.

Hydnora africana is dichogamous, that is, flowers are functionally pistillate the

first day and functionally staminate the second.

Fruit of Hydnora africana

Antheral ring does not closein H. johannis

Is H. johannis dichogamous?

Continuing research

--Determine pollinators and dispersers

--Study population structure

--Determine relationship among species

Meanwhile, back at home. . .

Can similar pollination syndromes befound in the Aristolochiaceae?

Aristolochia macrophylla

Hexastylis virginica

Aristolochia clematis

Note fused androecium

With Thanks to. . .

Piet Vorster, Department of BotanyStellenbosch University, Stellenbosch

Outstanding Hydnora hunter,Libby Musselman

Erika Maass, Department of Biology,University of Namibia,

Windhoek