Aspleniaceae, Newman, 1840

Fischer, Eberhard & Lobin, Wolfram, 2023, Synoptic Revision of Aspleniaceae (Asplenium, Hymenasplenium) of Rwanda, Phytotaxa 608 (1), pp. 1-65 : 58-59

Phytogeography of Aspleniaceae in Rwanda

In Rwanda 45 species of Aspleniaceae have been recorded, among them 44 species of Asplenium and one species of Hymenasplenium . This is remarkably rich for a country of only 26.388 km ². In Tropical East Africa ( Uganda, Kenya, Tanzania) 64 species are known ( Beentje 2008) and in continental Africa, this figure reaches a total of 120 species ( Viane 2021). Thus, Rwanda harbours 37.5% of all known Aspleniaceae from continental Africa.

The phytogeographic relationships of the Aspleniaceae from Rwanda are briefly analyzed here:

Two species, Asplenium adiantum-nigrum and A. trichomanes subsp. quadrivalens have a cosmopolitan distribution. In Africa they are usually confined to the Afromontane region.

Only one species, Asplenium inaequilaterale , shows a pantropical distribution, occurring in America, Africa and Asia.

Two species, Asplenium erectum and A. normale , occur in Africa and Madagascar and extend to Asia ( India to Japan).

Asplenium aethiopicum and A. lividum are found in Africa and Madagascar, extending to Arabia

Asplenium monanthes is widely distributed in Africa to Southern Africa, Madagascar, North and South America, extending to Azores, Madeira and Canary Islands.

Asplenium protensum occurs in continental Africa to Southern Africa, and in Madagascar, the Comoros and Arabia ( Yemen).

The following six species have an afromontane distribution, occurring in the mountains of West, East and Southern Africa and often extending to Madagascar: Asplenium abyssinicum , A. boltonii , A. megalura , A. preussii , A. sandersonii , A. theciferum .

Species occurring in the mountains of East and South Africa, often extending to Madagascar, are: Asplenium christii , A. dregeanum , A. friesiorum , A. hypomelas , A. linckii , A. mannii , A. rutifolium , A. smedsii .

The following species are confined to mountains of East Africa in the Albertine Rift with the Ruwenzori Massif to the highlands of Ethiopia, Mt. Kenya, Kilimanjaro or Eastern Arc Mountains (above 1500 m) and can be defined as Eastern-Afromontane: Asplenium bugoiense , A. ceii , A. elliottii , A. mildbraedii , A. stuhlmannii .

Eastern afroalpine elements occurring in the upper zones of Ruwenzori, the Virunga Massif, and Kilimanjaro above 2500 m are Asplenium sertularioides , A. uhligii , A. volkensii .

Guineo-Congolian species found in lowland to mid-altitude rainforests from Western Africa to Central Africa, extending to Uganda or Western Tanzania are: Asplenium africanum , A. cancellatum , A. gemmascens .

The most remarkable phytogeographic elements are the Albertine Rift endemics (see Plumtre et al. 2007). The Albertine Rift comprises the mountains along Tanganyika- and Kivu-Lake, north to Edward and Albert Lake, and is situated in Eastern Congo (Itombwe Mountains, Kahuzi-Biéga-National Park, Ruwenzori), Rwanda (Nyungwe National Park, Volcano National Park, Gishwati-Mukura National Park), Burundi (Kibira National Park, Bururi), Western Uganda (Bwindi Impenetrable Forest, Budongo Forest) and Western Tanzania (Mahale, Gombe). The majority of Albertine Rift endemics in Asplenium are confined to Kahuzi-Biéga, Ruwenzori, Nyungwe, Gishwati-Mukura and Volcano and Kibira National Park: Asplenium burundense , A. centrafricanum , A. majus , A. markusbeckeri sp. nov., A. musiraense , A. ramicola sp. nov., A. rukararense , A. tenuicaudatum , A. uschiae sp. nov.

Within Rwanda most species occur in Nyungwe National Park, where 24 species have been recorded. In Cyamudongo Forest, an isolated forest patch of ca. 300 ha that is part of Nyungwe National Park, 14 species are found, among them five ( Asplenium africanum , A. ceii , A. christii , A. inaequilaterale , and A. uschiae sp. nov.) that are restricted to Cyamudongo within Rwanda. Fifteen Asplenium species are known from the Volcano National Park and six of these species ( Asplenium adiantum-nigrum , A. majus , A. sertularioides , A. trichomanes subsp. quadrivalens , A. uhligii and A. volkensii ) only occur there in Rwanda. In the isolated Ibuhanga Forest four species are known, and it is the only Rwandan location of Asplenium lividum and A. markusbeckeri sp. nov. The highly fragmented Gishwati-Mukura National Park harbours eight species. In Akagera National Park four species have been recorded on rock outcrops ( Asplenium stuhlmannii ) or in dry forests ( A. musiraense ) and gallery forests ( A. rutifolium , A. theciferum ). Six species occur outside the National Parks either in planted forests ( Asplenium aethiopicum , A. elliottii , A. friesiorum , A. musiraense , A. theciferum ) or on rock outcrops in Eastern Rwanda ( Asplenium musiraense , A. stuhlmannii ).