Host-specific germination of the root holoparasite Hydnora triceps (Hydnoraceae)

Abstract

We provide the first germination data on the root-holoparasitic Hydnoraceae. Aqueous root extracts of host and non-host Euphorbia spp. were applied to seeds of Hydnora triceps Drège & Meyer, a narrow endemic of Namibia and South Africa. The seeds of H. triceps germinated only in response to root extracts of its exclusive host, Euphorbia dregeana Meyer, and not for co-occurring non-host Euphorbia spp. This pattern of host specific germination suggests that germination response to host-root cues may be responsible for host partitioning. Provenance of H. triceps seeds and E. dregeana root extracts did not significantly affect germination rates. The round-eared elephant shrew ( Macroscelides proboscideus ) and the striped mouse ( Rhabdomys pumilio ) were observed feeding on the fleshy pulp of H. triceps fruits. Small-mammal droppings collected from the same partially consumed fruits contained intact seeds (1.9 ± 1.1 seeds/dropping) providing indirect evidence of seed dispersal by small mammals.