Included here is the island of Socotra in the Arabian Sea just north of Somalia. The climate is monsoonal but much less arid than the adjacent mainland.

Socotran Dendrosicyos Limestone Vegetation

On the lower slopes of the limestone plateau the characteristic plant is the endemic Dendrosicyos socotrana (Cucurbitatceae). Other endemics found here include Adenium sokotranum (Apocynaceae), Cissus subaphylla (Vitaceae) and Euphorbia arbuscula (Euphorbiaceae) and form a landscape unique to Socotra.  Dendrosicyos socotrana, commonly known as the cucumber tree, is the only known member of the cucumber family (Cucurbitaceae) that has evolved into a tree. Associated endemic shrubs include Maerua socotrana (Capparidaceae), Withania riebeckii (Solanaceae) and Cynanchum linifolum (Asclepiadaeae), while low growing species include endemic herbs such as Corchorus erodioides (Tiliaceae), Oldenlandia pulvinata (Asclepiadaceae), Trichodesma microcalyx (Boraginaceae), Lactuca rhynchcarpa, Pulicaria stephanocarpa and P. diversifolia (Asteraceae), and the endemic fern Adiantum balfourii (Adiantaceae).

Socotran Dorstenia-Kleinia-Ficus Limestone Vegetation

This plant formation occurs on limestone at heights above 500 m. The characteristic endemics include Dorstenia gigas and Ficus socotrana (Moraceae) and Kleinia scottii (Asteraceae).  Other common endemics include Tatragonia pentandra (Aizoaceae), Euphorbia oblanceolata (Euphorbiaceae) and Hibiscus scottii (Malvaceae). The rock ledges support endemics such as Pseudomussaenda capsulifera (Rubiaceae), Haya obovata, Polycarpaea divaricata (Caryophyllaceae), while pockets of dark rich soil include the endemic Begonia socotrana (Begoniaceae), Exacum affine (Gentianaceae) and Pseuedanum caudatum (Apiaceae).

Socotran Limestone Valley Thickets

In sheltered valleys, especially where the soil is well developed, dense thickets occur. In the area around Reiged at an altitude of about 900 m the commonest shrubs and trees in these thickest include various endemics such as Acacia pennivenia (Fabaceae), Acridocarpus socotranus (Malpighiaceae), Croton sulcifructus, Dicliptera effusa (Euphorbiaceae), Rhus thyrsiflora (Anacardiaceae), Ruellia insignis (Acanthaceae), Psiadia schweinfurthii, and Vernonia cockburniana (Asteraceae). These in turn support various endemic lianas and creepers such as Cissus paniculata (Vitaceae), Discorea lanata (Discoriaceae) and Tragia balfouriana (Euphorbiaceae).

Socotran Dracaena-Boswellia Limestone Vegetation

The strange mushroom shapes of the endemic dragon tree, Dracaena cinnabari (Liliaceae) makes this one of the most distinctive communities in the world. The tree is also the source of the mysterious dragon’s blood, a type of resin that oozes from between the branches. The substance, originally thought to be made from dragons, turns red on cooking, and is in much demand throughout Arabia for its magical and curative properties. Other common endemics include Boswellia ameero, B. elongata, B. socotrana (Burseraceae), and Mitolepis intricata (Asclepiadaceae). The well-known aromatic resin frankincense, which is burned as incence, is derived from Boswellia socotrana.  This community is characteristic of the limestone slopes of the Hamadera Hills.

Socotran Limestone Plateau Vegetation

In contrast to the slopes, the limestone plateau is remarkable arid mainly supporting just a few stunted bushes of the endemic Jatropha unicostata (Euphorbiaceae) together with occasional specimens of Adenium sokotranum, Croton socotranus and Ficus socotranus.  Adenium sokotranum is commonly known as the sack-of-potatoes tree and has been described as the slug of the tree world - some individuals even suggest human form.  The annual vegetation is largely composed of grasses such as Arthraxon lancifolius, Aristida funiculata and Pennisetum setaceum. However, the paucity of the vegetation is thought to be as much to do with the high winds experienced in this exposed area as it is to the aridity.

References

Miller, A. G. & Morris, M. 2004. Ethnoflora of the Soqotra Archipelago. The Royal Botanical Gardens, Edinburgh.

Popov, G. B. 1957. The vegetation of Socotra. Journal of the Linnean Society Botany, 55: 706-720.

White, F. 1983. The Vegetation of Africa. UNESCO.