Endemism and geographic distribution of African Thismiaceae
Background and aim – The occurrence of the enigmatic plant family Thismiaceae has never been characterized in detail, but appears to be focused in three vegetation types. This study used data from the literature, in tandem with detailed new field data from Cameroon, to document, map, and predict potential distributions of Thismiaceae species across Africa, and relate their occurrence to features of climate.
Methods – We reviewed known occurrences of Thismiaceae species across Africa; in Cameroon, Thismiaceae occurrences were studied in 22 1-ha plots (220 000 m2), at lowland, sub-montane, and montane sites in evergreen forest, semi-deciduous forest, and woody and grassland savannah vegetation types. Assembling known occurrences from across the continent, ecological niche modeling was used to map potential geographic ranges of African Thismiaceae under present-day climate conditions across Africa.
Results and discussion – In Cameroon fieldwork, 338 individual Thismiaceae were recorded, corresponding to eleven species of Afrothismia. The most occupied vegetation type for Thismiaceae was sub-montane forest. Occurrence of Thismiaceae seems to depend principally on rainfall, as most specimens were recorded in areas with high rainfall, about six weeks after the first rains, toward the middle or end of the rainy season. This pattern seems to be consistent across all of the species. Soil analyses shows that Afrothismia was most frequent under conditions of low calcium (0.09–15.21 %) and pH of 3.58–6.16. Niche models predicted that additional Thismiaceae populations may be discovered at high-rainfall sub-montane forest sites in Democratic Republic of Congo, Rwanda, Tanzania, and Kenya. Across tropical Africa, the Thismiaceae comprise 22 species in two genera (twenty Afrothismia and two Oxygyne), recorded from seven countries. Many of these species are narrowly endemic to one or a few specific sites, so that detailed knowledge of distributional patterns is important for their conservation.