Formations in the Somalo-Ethiopian BioProvince

Peter Martin Rhind

Somalo-Ethiopian Acacia-Commiphora Deciduous Bushland These bushlands form the climax vegetation over much of this BioProvince. They are often dense and can reach heights of 5 m with scattered emergent trees up to 9 m. In places they forms an impenetrable thicket made more so by many spiny species. In fact, all of the dominant Acacias and many of the Commiphoras are covered in spines. Although there is considerable variation in floristic composition, species of Acacia, Commiphora, Grewia and Capparidaceae are nearly always present. Characteristic taxa of the canopy include Acacia bussei, A. mellifera, A. nilotica subsp. subalata, A. reficiens subsp. misera, A. thomasii, Commiphora africana, C. boiviniana, C. campestris, C. erythraea, C. mollis, C. schimperi, Balanites orbicularis, Boscia coriacea, Boswellia neglecta, Cadaba farinosa, Cassia abbreviata, Cordia ovalis, Dobera glabra, Euphorbia scheffleri, Hymenodictyon parvifolium, Lannea alata, Sesamothamnus rivae, Platycelyphium voense, Premna hildebrandtii, Salvadora persica, Sterculia africana, and endemics such as Givotia gosai (Euphorbiaceae), Terminalia orbicularis, T. parvula (of the Combretaceae) and Thylachium thomasii (Capparaceae). Common smaller bushes and shrubs include Bauhinia taitensis, Bridelia taitensis, Caesalpinia trothae, Combretum aculeatum, Carphalea glaucescens, Ecbalium amplexicaule, Ephretia teitensis, Grewwia fallax, and the endemic Caucanthus albidus (Malpighiaceae), Erythrochlamys spectabilis (Acanthaceae), Maerua denhardtiorum (Capparaceae), Sericocomopsis hildebrandtii and S. pallida (Amaranthaceae). Succulents are scattered throughout with the candelabra-like Euphorbia robecchii being one of the more characteristic species, while in some areas the cactiform Euphorbia grandicornis forms local thickets. Other stem succulents include Adenia obesum, Monadenium inventustum and the endemic Calyptrotheca somalensis and C. taitensis (Portulacaceae). There are also a number of succulent climbers such as Cissua quadrangularis and Sarcostemma viminale with their succulent, photosynthetic stems, Cissus rotundifolia with succuent , while Adenia globosa and Pyrenacantha malvifolia have immense water-storing tubers of up to 1 m in diameter. Other common climbers include Gerrardanththus lobatus, Kedrostis gijef, Pergularia daemia and Thunbergia guerkeana. These bushlands are extemely rich in endemic species with at least 230 occurring throughout the BioProvince, which includes at least 17 endemic species of Acacia, 29 endemic species of Aloa and 39 endemic species of Commiphora. However, many of the endemic species are quite localized and often confined to limestone and/or gypsum.

Examples of endemic species found in this habitat throughout the BioProvince include trees such as Albizia obbiadensis, Cordyla somalensis, Dalbergia commiphoroides, Dichrostachys kirkii, Dicraeopetalum stipulare, Lonchocarpus kanurii Senna baccarinii (), Boscia mazzocchii (Capparaceae), Boswellia rivae (Burseraceae), Euphorbia giumboensis, E. jatrophoides (Euphorbiaceae), Farsetia somalensis (Brassicaceae), Hildegardia gillettii (), Kirkia tenuifolia (Kirkiaceae), Lannea malifolia (Anacardiaceae), Moringa ruspoliana (Moringaceae), Turraea barbata (Meliaceae), shrubs such as Abutilon anglosomaliae, Gossypium frifurcatum, Hibiscus bricchettii, Pavonia eremogeiton, Sida ogadensis (), Acacia somalensis, Arthrocarpum somalense, Bauhinia leucantha, Caesalpinia oligophylla, Calliandra gilbertii, Cordeauxia edulis, Crotalaria incrassifolia, Dalbergia varandensis, Indigofera boranica, Microcharis nematophylla, Ormocarpum muricatum, Parkinsonia raimondoi, Rhynchosia gansole, Senna ruspolii, Tephrosia obbiadensis (Fabaceae), Basanthe berberoides (Passifloraceae), Bottegoa insignis (Ptaeroxylaceae), Calyptrotheca somalensis (Portulacaceae), Cissus ellenbeckii (Vitaceae), Commicarpus mistus (Nyctaginaceae), Commiphora horrida (Burseraceae), Dasysphaera alternifolia, Lopriorea ruspolii, Pupalia robecchii (Amaranthaceae), Euphorbia cryptospinosa, Jatropha dichtar (Euphorbiaceae), Eureiandra somalensis (Cucurbitaceae), Farsetia robecchiana (Brassicaceae), Grewia penicillata (Tiliaceae), Gyrocarpus angustifolius (Hernandiaceae), Halothamnus somalensis (Chenopodiaceae), Harmsia sidoides, Melhania hiranensis (Sterculiaceae), Kelleronia gillettiae (Zygophyllaceae), Limeum angustifolium (Molluginaceae), Loewia glutinosa (Turneraceae), Maerua candida (Capparaceae), Oxygonum altissimum (Polygonaceae), Polygala effusa (Polygalaceae), Triumfetta actinocarpa (Tiliaceae), climbers such as Adenia aculeata (Passifloraceae), Caucanthus albidus (Malpighiaceae), Cissus aphylla, Cyphostemma cornus-africani (Vitaceae), Cucumis hastatus and Dactyliandra stefaninii (Cucurbitaceae), Rhynchosia megalocalyx, Tylosema argentea, Wajira albescens (Fabaceae), and herbaceous species such as Amorphophallus laxiflorus, Stylochaeton grandis (Araceae), Aneilema somaliense, Cyanotis somaliense (Commelinaceae), Anthericum jamesii, Chlorophytum applanatum (Anthericaceae), Brachiaria breviglumis, Eragrostis psammophila (), Cleome gallaensis (Capparaceae), Farsetia longistyla, Matthiola erlangeriana (Brassicaceae), Indigofera davensis, Senna humifusa (Fabaceae), Kalanchoe subrosulata (Crassulaceae), Polygala bariensis (Polygalaceae), Psilotrichum gracilipes (Amaranthaceae), Reseda ellenbeckii (Resedaceae) and Sida floccosa (Malvaceae).

Somalo-Ethiopian Evergreen and Semi-Evergreen Bushland These bushlands are usually confined to the dryer slopes of mountains often forming an ecotone between montane forest, especially juniper forest, and the lowland Acacia- Commiphora bushland. Some of the best examples can be seen on the slopes of the Ethiopian Highlands. Although there is considerable variation in species composition, Carissa edulis, Dodonaea viscosa, Olea africana and Tarchonanthus camphoratus are nearly always present together with species of Acokanthera, Euclea, Sanservieria, Teclea and succulent species of Aloe and Euphorbia. On the Kedong escarpment near Nairobi they form an almost impenetrable thicket with a canopy up to 7 m high. The dominant crown species are Acokanthera schimperi, Euclea divinorum, Gnida subcordata, Olea africana, while other large bushes commonly include the endemic Canthium keniense (Rubiaceae). The cactoid stem- succulent Euphorbia candelabrum occurs as scattered emergents up to 9 m tall. The shrub layer typically comprises Aspilia mossambicensis, Psiadia arabica, Tinnaea aethiopica and Turraea mombassana, while the few climbers commonly include Capparis fascicularis, Pterolobium stellatum, Senecio petitians and Scuta myrtina. Apart from succulents, such as species of Crassula, Kalanchoe and Sansevieria, the ground layer is usually sparse, but may include shade tolerant grasses like Ehrharta erecta. In Somalia the principal bushes are Acokanthera schimperi, Buxus hildebrandtii, Cadia purpurea and Dodonaea viscosa, while other important species include the endemic Aloe eminens (Asphodelaceae) and Rhus somalensis (Anacardiaceae). Throughout these bushlands many more endemic species may be encountered including trees such as Acacia manubensis and Ceratonia oreothauma subsp somalensis (Fabaceae), Dovyalis verrucosa (Flacourtiaceae), Grewia truncata (Tiliaceae), Steganotaenia commiphoroides (Apiaceae), shrubs such as Diplolophium somaliense (Apiaceae), Fagaropsis hildebrandtii (Rutaceae), Hibiscus ahlensis (Malvaceae), Indigofera sedgewickiana, Ormocarpum somalensis (Fabaceae), Jatropha variablis (Euphorbiaceae), Maerua intricata (Capparaceae), Maytenus punctata, M. somalensis (Celastraceae), Melhania engleriana (Sterculiaceae), Polygala somaliensis (Polygalaceae), Rhus puccionii (Anacardiaceae), Thilachium thomasii (Capparaceae), Uvaria denhardtiana (Annonaceae), succulents such as Euphorbia fascicaulis and E. gillettii (Euphorbiaceae), and herbaceous species such as Chlorophytum petraeum (Anthericaceae), Crassula volkensis (Crassulaceae), Crotalaria leucoclada (Fabaceae), Eragrostis trachyantha (Poaceae), Pelargonium glechomoides (Geraniaceae), Polygala amboniensis (Polygalaceae), Rosifax sabuletorum (Amaranthaceae) and Zehneria somalensis (Cucurbitaceae).

Somalo-Ethiopian Afromontane Forest Ranging in altitude from about 1700 to 3300 m these forests are extremely varied with many broad-leaved hardwoods and a number of conifer species. Some of the more important trees are Ekebergia rueppelliana, Juniperus procera, Olea chrysophylla, Podocarpus gracilior and Pygmaeum africanum, but on some mountains, such as Mount Kenya, the formation has three distinct zones - a lower montane rainforest, a middle zone where the bamboo Arundinaria alpine often attains dominance, and a higher zone co-dominated by Hagenia abyssinica and Hypericum leucoptychodes. On Kilimanjaro both bamboo and Hagenia- Hypericum zones are lacking. The endemic species found within these montane forests often straddle more than one of the above-mentioned zones. Nevertheless, endemic species such as the grass Anthoxanthum nivale (Poaceae), the sedge Carex conferta (Cyperaceae), the woodrushs Luzula abyssicca and Luzula johnstonii (Juncaceae), and the giant orchid Habenaria eggelingii (Orchidaceae) are more often associated with lower zones, while endemic grasses such as Agrostis gracilifolia, Agrostis sclerophylla, pilgeri subsp pilgerii (Poaceae), together with herbaceous species like Bartsia kilimandscharica and B. longiflora (Scrophulariaceae), Galium ossirwaense (Rubiaceae), Peucedanum friesiorum (Apiaceae), Satureja simensis (Lamiaceae), Swertia lugardae (Gentianaceae), Valeriana volkensii (Valerianaceae), and shrubs like Helichrysum chionoides and Senecio snowdenii (Asteraceae) are typically associated with the bamboo zone. Endemic species often straddling two or more of these zones include the grass Helictotrichon milanjianum (Poaceae) and forbs like Bartsia macrophylla (Scrophulariaceae), Cerastium afromontanum and Stellaria sennii (Caryophyllaceae) and Crassocephalum ducis-aprutii (Asteraceae).

Somalo-Ethiopian Ericaceous Woodland Between altitudes of about 3000 to 4000 m montane forest gives way to woodland dominated by giant heaths and heath-like , especially on the wetter mountains such as Ruwenzori and the Virunga volcanoes. The endemic Philippia trimera (Ericaceae) is often dominant growing to heights of about 13 m. Other associated trees, possibly dominant in some cases, include the endemic Hypericum bequaertii and H. keniense (Hypericaceae), Philippa excelsa and P. johnstonii (Ericaceae), and Senecio erica-rosenii (Asteraceae), while other common plants include the almost arborescent endemic umbillifer Peucedanum kerstenii (Apiaceae). However, in some circumstances there may be very little Philippia or Erica and are largely replaced by the endemic Stoebe kilimandscharica - a member of the Asteraceae with an ericoid habit. The ground layer may include endemic grasses such as Agrostis kilimandscharica, A. leptophylla, A. trachyphylla, A, volkensii, Pentashistis borussica, P. minor, P. ruwenzoriensis [Ruwenzori], Poa schimperana (Poaceae) and various endemic forbs such as Anagallis serpens subsp. meyeri-johnannis (Primulaceae), Anemone thomsonii, Delphinium macrocentron (Ranunculaceae), Bartsia petitiana, Celsia scrophularaefolia, Veronica glandulosa (Scrophulariaceae), Carduus kenensis (Asteraceae), Geranium kilimandscharicum (Geraniaceae), Hypericum afromontanum [Elgon] (Hypericaceae) Lobelia lindblomii (Campanulaceae), Pimpinella kilimandscharica (Apiaceae), Satureja kilimandscharica (Lamiaceae), Trifolium burchellianum var. johnstonii (Fabaceae), and in the marshy areas the orchid Disa stairsii (Orchidaceae) and sedge Carpha eminii [Ruwenzori] (Cyperaceae), There may also be several endemic megaphytic lobelia herbs such as Lobelia bequaertii [Rumenzori] and L. keniensis (Campanulaceae). Endemic shrubs may include several shrubby alchemillas such as Alchemilla elgonensis, A. roccatii, A. stuhlmannii and A. triphylla (Rosaceae), together with Blaeria folago (Ericaceae), Hypericum kiboense (Hypericaceae), Protea kilimandscharica (Proteaceae), Senecio rhammatophyllus (Asteraceae) and Thesium kilimandscharica (Santalaceae).

Somalo-Ethiopian Dendrodsenecio Woodlands The spectacular woodlands are one of the most unique plant communities in the afro- mountains. The subgenus Dendrosenecio is represented in different mountains by different but closely related endemic species. They normally grow between 4-6 m tall and may form dense forests as on Ruwenzori and the Virunga volcanoes, whereas on Aberdare, Elgon and Mt Kenya they are much more open, and on Kilimanjaro only occur as scattered stands. The altitude of these forests varies from mountain to mountain - on Ruwenzori they range from 3800 to 4350 m. The main species are Senecio (Dendrosenecio) erici-rosenii and S. adnivalis on Virunga, S. elgonensis and S. barbatipes on Elgon, S. battiscombei and S. brassiformis on Aberdare, S. brassica and S. keniodendron on Mt Kenya, and S. cottonii and S. kilimanjari on Kilimanjaro. Often intermingled with these are various endemic, macrophytic lobelias (Campanulaceae) such as Lobelia lanuriensis, L. telekii and L. wollastonii. These typically grow to heights of between 2 and 4 m, but L. lanuriensis can achieve 7 m. Typically the scrub layer is dominated by shrubby, endemic alchemillas (Rosaceae) including Alchemilla argyrophylla, A. elgonensis and A. johnstonii - the latter often forming a dense scrub on Virunga. Of particular interest in the ground layer are the many temperate and boreal elements, some of which like Arabis alpina and Descampsia flexuosa are taxonomically indistinguishable for their counterparts in northern Europe, whereas others like Cerastium octandrum var. adnivales (Caryophyllaceae), Myosotis keniensis (Boraginaceae) and Valeriana kilmandscharica (Valerianaceae) have become distinct endemics. Other endemic ground layer species include Alchemilla microbetula (Rosaceae), Carduus ruwenzoriensis [Ruwenzori], Crassocephalum ducis-aprutii and Senecio polyadenus (Asteraceae). Finally, another interesting feature of this community on Ruwenzori is the endemic climber Galium ruwenzoriense (Rubiaceae), which can climb to heights of 5 m or more on the giant senecios.

Somalo-Ethiopian Helichrysum Scrub This is another very striking and characteristic community of the afroalpine belt, and can be found on Kilimanjaro, for example, at altitudes of 4100 to 4300 m. It is dominated by various endemic, shrubby members of the Helichrysum (Asteraceae), and is particularly impressive on Ruwenzori where the dominant species Helichrysum stuhlmannii forms a thicket up to 2 m high. The main species on other mountains are H. newi on Virunga, H. amblyphyllum and H. citrispinum on Elgon, H. chionoides and H. newi on Aberdare, H. browneii, H. chionoides and H. citrispinum on Mt Kenya, and H. citrispinum and H. newii on Kilimanjara. The associated ground flora varies from place to place, but on Mount Kenya normally comprise a discontinuous stand of endemic grasses such as Agrostis leptophylla, A. trachyphylla, Calamagrostis hedbergii and Pentaschistis minor (Poaceae), while some of more common forbs include the endemic Nannoseris schimper and Senecio keniophytum (Asteraceae). On Kilimanjaro the endemic ground flora include grasses such as Festuca kilimanjarica and Pentaschistis borussica (Poaceae) together with Euryops dacrydioides and Senecio meyeri-johannis (Asteraceae).

Somalo-Ethiopian Alchemilla Scrub Shrubby alchemillas are another unusual feature of the afromountains. Most species in this genus are herbaceous, but here they form extensive scrublands. They include by a number of endemic species. Alchemilla johnstonii is often dominant but in slightly dryer areas A. argyrophylla, A. elgonensis, and A. subnivalis become prominent. Ground layer species vary from mountain to mountain, but on Elgon normally include endemics such as Poa schimperiana (Poaceae), Valeriana kilimandscharica (Valerianaceae), Veronica glandulosa (Scrophulariaceae) and Viola eminii (Violaceae). Other endemic species often associated with this type of vegetation include Agrostis mildbraedii (Poaceae), Helichrysum newii (Asteraceae), Heracleum elgonense (Apiaceae) and Lobelia elgonensis (Campanulaceae).

Somalo-Ethiopian Tussock Grassland Dominated by tufted, mostly endemic grasses such as Agrostis trachyphylla, A. volkensii, Andropogon amethystinus, Festuca abyssinica, F. kilimanjarica, F. pilgeri, Koeleria gracilis, Poa leptoclada and species Pentaschistis (Poaceae) this is one of the most widespread vegetation types in the afroalpine belt, particularly on dryer mountains such as Elgon, Mount Kenya and Kilimanjaro. The associated vascular plants vary from site to site, but on Mount Kenya normally include a mixture of non-endemics such as Arabidopsis thaliana and Cardamine oblique and endemics such as Galium glaciale (Rubiaceae) and Senecio purtschelleri (Asteraceae), while on Kilimanjaro other endemics may include Haplosciadium abyssincia (Apiaceae) and Satureja kilimandschari (Lamiaceae). On the wetter Rumenzori a different assemblage of grasses are present including the widespread Descampsia caespitosa and the endemic Anthoxanthum nivale (Poaceae), but grasslands here are relatively scarce. This is also true for Mount Meru where one of the most important grasses is the local endemic Pentaschistis meruensis (Poaceae).

Somalo-Ethiopian Carex Bog In the lower, more level parts of the afroalpine belt where drainage is impeded there are bogs dominated by endemic, tussock-forming sedges. The main dominants are either Carex monostachya or C. runssoroensis (Cyperaceae), but the habitat is given a strange appearance by the presence of endemic giant lobelias (Campanulaceae). As the main sub- dominants these include Lobelia bequaertii on Ruwenzori, L. elgonensis on Elgon, L. sattimae of Aberdare and L. deckenii on Kilimanjaro. Other endemic plants may include Kenichloa chionogeiton (Poaceae), Luzula abyssinica, L. johnstonii (Juncaceae), Ranunculus stagnalis, R. volkensii (Ranunculaceae), Romulea keniensis (Iridaceae), Sagina afroalpina (Caryophyllaceae), Senecio transmarinus (Asteraceae) and Subularia monticola (Brassicaceae). The lower layers, however, are mainly dominated by sphagna and other bryophytes including endemic species such as Meesia kenyae and Scapania hedbergii on Mt Kenya, and Sematophyllum elgonense on Elgon.

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