Hydnora

Hydnora, genus of 8 to 10 species of parasitic flowering plants in the family Aristolochiaceae native to Africa, Madagascar, and the Arabian Peninsula.

Physical description

Lacking leaves and chlorophyll, Hydnora species are incapable of photosynthesis and are thus obligate parasites, meaning they are wholly dependent on their hosts for nutrition. The sprawling rhizomatous plants exist almost entirely underground and penetrate the roots of their hosts by means of haustoria.

The large unusual flowers arise directly from the root system, usually appearing after a heavy rainfall. Somewhat resembling a fungus, each thick, fleshy flower is composed of a single three-parted perianth that is peach-orange in colour with a brown, scaly exterior. They are foul-smelling and are pollinated by beetles, which are first trapped within the structure and coated with pollen before escaping their floral confines. The fruit, which matures slowly underground, is eaten and dispersed by animals, including birds, baboons, jackals, porcupines, and moles. The numerous seeds are minute and may stay dormant in the soil seed bank until certain chemical cues from the roots of a nearby host plant trigger germination.

The plants are remarkably host-specific but display a range of host preferences across the genus. The four species of Hydnora that grow in southern Africa exclusively parasitize succulent spurges of the genus Euphorbia (family Euphorbiaceae). Most East African species are dependent on Acacia trees (family Fabaceae), with the exception of one that parasitizes Commiphora trees (family Burseraceae).

Species

Formerly its own family (Hydnoraceae), the genus Hydnora is now placed in the subfamily Hydnoroideae with the Central and South American genus Prosopanche. One of the most common species, the southern African H. africana, is often known as jackal food. The astringent fruits are eaten raw or cooked, and the plant is used in traditional medicine to treat dysentery and other maladies. H. triceps and H. visseri are also both found in Namibia and South Africa.

Several species are found in the Arabian Peninsula, including H. arabica and H. abyssinica, which is also found throughout much of Africa. An East African species, H. sinandevu, ranges from Kenya to Tanzania, and at least one species, H. esculenta, is found in Madagascar.

In 2022 a new species, H. bolinii, was discovered in Ethiopia and Somalia.