Natural History of the Strangest Plants in the World

Natural History of the Strangest Plants in the World August 2003 Hydnora africana, Karasburg District, Namibia Lytton John Musselman Old Dominion University 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 herbs Achlorophyllous Obligate parasites Systematic position of the Hydnoraceae has long been debated due to extreme morphologial reduction. Molecular data place Hydnoraceae with Aristolochiaceae “Palaeoherbs” Taxonomy Only two genera comprise the 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. Hydnora-African • H. esculenta-Madagascar, a poorly known species. • H. sinandevu-Kenya and Tanzania, described in 2002. Prosopanche-New World • P. americana -widespread on species of Prosopis (Fabaceae). • P. bonacinae-Diversity of hosts. Prosopanche-New World Hydnora-Old World Predicted distribution of Gondwanaland paleoherbs Prosopanche Prosopanche americana, Cordoba Province, Argentina Hydnoraceae flowers are chamber flowers A chamber is present above the stigma. Chamber Prosopanche americana What is the function of the chamber? Chamber Prosopanche americana For the insect-It provides a place for the insect visitor to spend the night. Mating often takes place. Chamber Prosopanche americana For the plant-It provides a “holding room” while the flower changes sex. Chamber Prosopanche americana Flower structure of Prosopanche americana Androecium Gland Stigma Prosopanche americana Prosopanche americana Prosopanche americana Pistillate phase Day one Prosopanche americana Staminate phase Day two Prosopanche flowers are dichogamous, that is, have distinctly staminate (male) and pistillate (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 Host: Prosopis alba Male phase Female phase Fruit Hydnora Floral Syndromes and Hosts Hydnora johannis Acacia spp. (Fabaceae) Beetles Hydnora africana Euphorbia spp. Beetles Hydnora triceps Euphorbia dregeana ??? Hydnora esculenta ??? ??? Osmophores Hydnora triceps-osmophores are in folds of perianth Hydnora africanaosmophores are elongate Hydnora abyssincaosmophores are tips of perianth Oldest flowers on left Is the osmophore in H. johannis unique? Mature flower Immature flower Recent research on Hydnora triceps Namaqualand Namaqualand Port Nolloth Center of diamond dredging, diamond smuggling….and Hydnora 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. Succulent Karoo near Port Nolloth, South Africa Rainy season, September 2001 Euphorbia dregeana, host of H. triceps Dry Season, December 2002 Distribution of Hydnora africana is related to that of its common host, Euphorbia gregaria Assumption: 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. Is the distribution of the parasite dependent upon the host? Hydnora triceps found only on E. dregeana Namibia Rosh Pinnah--First Namibian collection Orange River South Africa Previously known collections of H. triceps at red arrow The sole evidence of Hydnora triceps ?? Hydnora triceps flowers underground!! Hydnora triceps is the only known dicot with underground flowers! Hypogeous flowering known 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 Day one Opening to chamber is open on day one Stages in Development Day one Day two Opening to chamber closes on day two Opening to chamber is open on day one Fruits previously unknown. Fruits of Hydnora triceps Fruits hollowed out by unknown animal. Hypogeous flowering and fruiting known only in H. triceps Hydnora africana Day one Day two Day one Day two-Staminate Day one-Pistillate Day two plus Day two Day one Floral visitors can be trapped in flowers when ring closes. Closed antheral ring. 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 close in 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 be found in the Aristolochiaceae? Aristolochia macrophylla Hexastylis virginica Aristolochia clematis Note fused androecium With Thanks to. . . Erika Maass, Department of Biology,University of Namibia, Windhoek Piet Vorster, Department of Botany Stellenbosch University, Stellenbosch Outstanding Hydnora hunter, Libby Musselman