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
Fruit
Female phase
Hydnora
Floral Syndromes and Hosts
Hydnora johannis
Acacia spp. (Fabaceae)
Beetles
Hydnora africana
Euphorbia spp.
Beetles
Hydnora triceps
Euphorbia dregeana
???
Hydnora
esculenta
???
???
Osmophores
Hydnora africanaosmophores are elongate
Hydnora triceps-osmophores are
in folds of perianth
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