DIVERSITY & ENDEMISM
Although research into the flora of the Horn of Africa is still ongoing, the best possible estimates are that there are about 5,000 species of vascular plants in the region, just over half of which – about 2,750 species – are endemic. There are strong concentrations of endemic species in northern Somalia and in the Socotra Archipelago.
Socotra also has a relatively high level of generic endemism, with 13 of the hotspot's nearly 60 endemic genera confined to the archipelago. Furthermore, the Horn of Africa is home to two endemic plant families: Barbeyaceae, which is represented by a single, relatively widespread evergreen species, Barbeya oleoides, and Dirachmaceae, represented by two threatened species, Dirachma socotrana (VU), on Socotra, and D. somalensis (EN) in central Somalia.
For thousands of years, several native tree species have provided the raw materials for some of the Horn of Africa’s most important commodities, including frankincense (from Boswellia sacra in Somalia, Yemen and Oman, and B. frereana in Somalia), myrrh (from the widespread Commiphor myrrha and C. guidottii in Somalia and eastern Ethiopia) and dragon's blood or cinnabar (from Dracaena cinnabari, EN found on Socotra). All three are gum-resins obtained from these trees. Dragon's blood, is used as a medicine and dye. The production of frankincense and myrrh is still a major economic activity in Somalia and, to some extent, in Ethiopia and northern Kenya.
Among the hotspot's other notable plant species is the spectacular cucumber tree (Dendrosicyos socotrana, VU), found only on Socotra, which has a massive water-storing trunk and tendrils on its branches. The daban or Bankoualé palm (Livistona carinensis, VU) is interesting in that the other 30 or so species of Livistona occur in Southeast Asia and Australia. The daban, which is harvested for use in the construction of homes and drainage pipes, is now found only in a few isolated localities in northeastern Somalia, Djibouti and southern Yemen. The Yeheb nut (Cordeauxia edulus, VU), an evergreen shrub or small tree with yellow flowers and edible, highly nourishing seeds is found in the dry bushlands of eastern Ethiopia and central Somalia, usually in areas of deep sand. It has been touted as a potential food crop for arid areas, but has proven difficult to cultivate.
Hundreds of new species have been discovered in Somalia alone in the last 20 years, most notable among them the Somali cyclamen (Cyclamen somalense). Known only from a small area in northern Somalia, the plant was a surprising discovery in tropical Africa, as the genus Cyclamen is otherwise found only in the Mediterranean region.
Of the 697 bird species regularly recorded in the hotspot, 24 are endemic. Seven of these species are found only in Somalia, including a bushshrike, the Bulo Burti boubou (Laniarius liberatus, CR), which was described (and is still known only) from a single individual that was released (hence the specific name liberatus) after comprehensive study. Another six species are confined entirely to Socotra, including the golden-winged grosbeak (Rhynchostruthus socotranus), the only representative of its genus. Four Endemic Bird Areas, as defined by BirdLife International, fall entirely within the hotspot.
One of the most notable endemic bird species in the hotspot is the Warsangli linnet (Carduelis johannis, EN), locally common in high, steep escarpments along the Gulf of Aden in northern Somalia. Another important flagship species is the Djibouti francolin (Francolinus ochropectus, CR), which is found only in two sites in Djibouti, Forêt de Day, which is thought to be the only viable site for this imperiled species, and the nearby Mabla Mountains.
Nearly 220 mammal species are found in the Horn of Africa, although only about 20 are endemic to the hotspot. The most notable endemics are several antelope species, including the beira (Dorcatragus megalotis, VU), dibatag (Ammodorcas clarkei), Speke's gazelle (Gazella spekei) and silver dikdik (Madoqua piacentinii, VU). The beira is confined to dry and inhospitable hills and mountains of northern Somalia, eastern Ethiopia and Djibouti, where it can survive without water. The slender dibatag, with its characteristic erect tail and long neck, is found in the bushlands of eastern Ethiopia and adjoining lowlands of northern and central Somalia. Both species have suffered from uncontrolled hunting and habitat degradation. The hotspot also has an endemic species of wild ass, the Somali wild ass (Equus africanus somaliensis, CR), while the desert warthog (Phacochoerus aethiopicus), a distinct species from the common warthog (P. africanus), is found mainly in eastern Ethiopia, Somalia and northern Kenya.
Five monotypic mammal genera are endemic to the hotspot, including the aforementioned beira and dibatag, as well as three small mammals: the Somali pygmy gerbil (Microdillus peeli), the ammodile (Ammodillus imbellis, VU) and Speke's pectinator (Pectinator spekei).
The hamadryas or sacred baboon (Papio hamadryas), which was held sacred in ancient Egypt and often mummified, is today endemic to the arid Horn, living on hillsides and escarpments bordering the southern Red Sea and the Gulf of Aden.
The Horn of Africa's highest levels of endemism occur among reptiles, with more than 90 of around 285 species found nowhere else. The hotspot's six endemic reptile genera include Haackgreerius, a monotypic genus of skink found in Somalia, and Aeluroglena, which is represented by a single species of snake, A. cucullata. Half of the endemic genera are restricted to Socotra, including the two Haemodracon gecko species and two snake genera, Ditypophis and Pachycalamus, represented by single species.
Unlike the reptiles, amphibians are relatively poorly represented in the arid Horn, with nearly 30 species recorded, of which at least six are endemic. There is only a single endemic genus, Lanzarana, which is represented by one species, Lanza's frog (L. largeni) of Somalia. Despite suitable habitats, no amphibians are known to exist on Socotra.
There are an estimated 100 species of freshwater fish in the Horn of Africa, about 10 of which are endemic. These endemics include three cave-dwelling species (each the only representative of an endemic genus) found only in Somalia, two of which – the Somalian blind barb (Barbopsis devecchii, VU) and Somalian cavefish (Phreatichthys andruzzii, VU) – are blind. No native freshwater fishes are known with certainty from Socotra, but populations of Aphanius dispar have been introduced to some waters as part of an anti-malaria program.