The Gerire Hills, a SE Ethiopian outpost of the transitional semi-evergreen bushland: vegetation, endemism and three new species, Croton elkerensis(Euphorbiaceae), Gnidia elkerensis(Thymelaeaceae), and Plectranthus spananthus(Lamiaceae)

ABSTRACTThe vegetation of the plateaux of the Gerire Hills, of unique geology, represents an outlier of the Transitional semi-evergreen bushland of the eastern escarpment of the Ethiopian highlands, about 160 km from continuously distributed vegetation of this type. In the lowland surrounding the hills is deciduous Acacia-Commiphorabushland, typical of the Somalia-Masai region. Unpublished data from a 1937 Italian expedition documents past existence of Juniperus proceraon the plateaux. Three new narrowly endemic species are described here from recently collected material: Croton elkerensisFriis & M.G. Gilbert (Euphorbiaceae), Gnidia elkerensisFriis & Sebsebe (Thymelaeaceae), and Plectranthus spananthusA.J. Paton, Friis & Sebsebe (Lamiaceae). Three previously described species from the hills, Blepharispermum obovatumChiov. (Asteraceae), Aloe elkerrianaDioli & T.A.McCoy (Aloaceae) and Euphorbia bertemariaeBisseret & Dioli (Euphorbiaceae), are narrow endemics. The species most similar to the bushland endemics occur in a range of vegetation types and phytochoria in East Africa south of Ethiopia or more widespread in Africa. The species most similar to the succulent endemics occur elsewhere in semi-evergreen bushland on limestone at the mountain range in northern Somalia. The Gerire Hills endemics are considered Vulnerable (VU) or Least Concern (LC) given the differing threats to their respective habitats.