Biogeography of Malvaceae
East Africa here includes Tanzania, Kenya, Burundi, Rwanda and Uganda, and Northeast Africa Somalia, Ethiopia, Eritrea, Djibouti and Sudan.
Aluka  has the species descriptions from Flora of Somalia and Flora of Tropical East Africa (covering Kenya, Uganda and Tanzania - Sterculiaceae and Tiliaceae only; Bombacaceae are absent, the Malvaceae volume has not yet been published), . Overviews of distribution in those works, and also in Flora Zambesiaca and Flora of West Tropical Africa (also at Aluka) give partial coverage of the other countries in the region. The distribution maps from the African Flowering Plant Database  are used to supplement this. However they do not always represent the complete distributions of a species, and are not available for all taxa.
Additionally there is an online checklist of the flora of Djibouti , and a flora of the Uganda-Sudan border region .
Due to the non-availability of complete coverage for all areas the lists cannot be guaranteed to be exhaustive. In particular the country lists for Rwanda and Burundi should probably should be more extensive.
The vegation is quite diverse. It is predominantly dry tropical forest and tree or bush savanna. The north of Sudan is desert and semidesert. Eritrea, northeastern Ethiopia and northern Somalia are also semidesert, as is a region in the interior of northern Kenya and southern Ethiopia. Montane forests, grasslands and moorlands occur in the mountains flanking the Ethiopian and Albertine (Western) Rifts, and in the mountains of the Eastern Arc of southern Kenya and Tanzania. Mangrove and rainforest occurs in the eastern coastal strip.
East and North East Africa comprises parts of several different phytogeographic regions. The Somali-Maasai region (xeric bushlands) is mostly in East (much of Kenya, north-central Tanzania) and North East Africa. (Eritrea, eastern Ethiopia and Somalia), but also extends across the Red Sea into Yemen. The Afromontane region is also mostly in East and North East Africa, but extends into the Democratic Republic of the Congo to the west. Northern Sudan forms the eastern end of the Saharan region (desert and semi-desert), and northern Uganda, southern Sudan, western Ethiopia and Eritrea the eastern end of the Sahelo-Sudanian region (tree savanna). A major wetland region, the Sudd of southern Sudan, interrupts the tree saveana. Much of Tanzania forms the northern part of the Zambezian open forest (miombo). The coastal strip from southern Somalia southwards forms the northern part of the Zanzibar-Inhambane region, who southern region comprises the coasts of Mozambique and Natal.
The region contains over 400 species belonging to 49 genera of the family Malvaceae. All of the subfamilies, except Tilioideae, are represented, but the representatives of Brownlowioideae and Helicteroideae, and to a lesser extent Sterculioideae, are plants of wet tropical forests found on the margins of the region. East Africa has a somewhat more diverse malviflora (300+ species) than North East Africa (250+) species. The most diverse national flora is that of Tanzania (which shares many species with the countries to its south), followed by Ethiopia.
About one third of the species belong to the two largest genera Hibiscus (75 species, of which 1 is introduced) and Grewia (68 species). Other significant genera are Abutilon (19 species, of which 1 is introduced), Cola (21 species) Corchorus (16 species, of which 1 is introduced), Dombeya (14 species), Hermannia (21 species), Melhania (27 species), Pavonia (36 species), Sida (20 species) and Triumfetta (26 species).
Hibiscus (Malvoideae: Hibisceae) is a pan-tropical genus.Several of the species found in eastern Africa are widely distributed within the Palaeotropics, but others are more narrowly distributed. Pavonia is a pan-tropical genus, which is predominatly neotropical. However, outside the America, the genus is most diverse in the bushlands of Ethiopia, Somalia, Kenya and Tanzania. Oher genera of Hibisceae which occur within the region are Abelmoschus (1 species), Fioria (2 species), Kosteletzkya (3 species), Malachra (1 species), Senra (1 species), Symphochlamys (1 species, endemic to Somalia), Talipariti (1 species) and Urena (1 species).
Grewia (Grewioideae) is a palaeotropical genus, of semi-arid forests and woodlands, found from southern Africa and Madagascar through southern Asia to Queensland and the western Pacific. Within the region the genus is most diverse in Tanzania. Corchorus and Triumfetta are pantropical genera. Within the region their distribution pattern parallels that of Grewia, but the contrast in diversity between countries is less marked. Sparrmannia (1 species) is found from South Africa to Ethiopia, and also in Madagascar,
Hermannia (Byttneriioideae: Hermannieae) is a genus concentrated in southern Africa with its greatest diversity in Western Cape (20 species in the Cape Peninsula alone) and Northern Cape. There are 4 species recorded from Mexico and adjacent parts of the United States, 1 from Australia, 1 from Madagascar (which is also widespread in Africa). Of the 21 species in East and North East Africa Hermannia modesta extends from Cape Province though East Africa to the Horn of Africa, the Sudan, Egypt and Arabia, and Hermannia tigrensis ranges from Angola and Zimbabwe to Ethiopia and West Africa. Of the other genera of Hermannieae two species of Melochia, and a single species of Waltheria also occur.
Melhania (Dombeyoideae) has a palaeotropical distibution, with a centre of diversity in Somalia and Ethiopia. Dombeya (Dombeyoideae) is centred on Madagascar and the Mascarene Islands, and is also found throughout Subsaharan Africa, where it is most diverse in the east. Harmsia (2 species) is endemic to the coasts of Kenya and Somalia.
Abutilon and Sida (Malvoideae: Malveae: Abutilinae) are pantropical genera. Like Pavonia they are most prevalent in the Somali-Maasai region. Other genera of Malveae present are Lavatera (1 species, endemic to Ethiopia), Malva (2 species, both introduced), Sidastrum (1 species) and Wissadula (1 species).
There are 4 genera of Gossypieae present in the region. Gossypium (9 species) and Cienfuegosia (4 species) are found in arid regions, and Gossypioides (1 species) and Thespesia (3 species) in the coastal fringe..
Cola is most diverse in Guinea-Congolian rainforest of west and central Africa. Three species extend into the region from that direction. Cola has a secondary area of diversity in the forests of the East African coastal zone, where there are 18 species, most of which are found in Tanzania. A few species extend northwards into Kenya and Somalia, and Kenya has a single endemic species. The remaining sterculioids have similar distributions. Hildegardia has two species in the coastal zone. Pterygota has one species in the coastal zone, and one species extending eastwards from the Guinea-Congolian forests. Octolobus has a single species, found at one site, representing an eastwards extension of a Guinea-Congolian distribution. Heritiera has a single species in the coastal zone (and widespread elsewhere on the coasts of the Indian Ocean). Sterculia is also most diverse in the coastal region, but has some species in dryer areas, and is found throught the region.
A number of other genera extend from the Guinea-Congolian region into the western fringes of the area, including helicteroids (Mansonia), byttnerioids (Bytternia, Leptonychia), brownlowioids (Carpodiptera, Christiana), dombeyoids (Nesogordonia) and grewioids (Clappertonia, Glyphaea). There is also one species of Leptonychia in the eastern coastal region.
Counts of genera by nation and region
Species counts for genera (numbers in brackets represent naturalised and casual species)
national counts for eastern Africa
Species distributions (N represents naturalised species, C casual species)
Byttnerioideae, Grewioideae, Brownlowioideae, Dombeyoideae, Helicteroideae, Sterculioideae, Bombacoideae, Hibisceae, Gossypieae, Malveae in East and North East Africa
Djibouti, Eritrea, Ethiopia, Somalia, Sudan
Burundi, Kenya, Rwanda, Tanzania, Uganda
Biogeography of Malvaceae
© 2010 Stewart R. Hinsley