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Editor: Wilhelm Giess
Euphorbia Sect. Tetracanthae Pax is considered to be morphologically and phylogenetically homogeneous. Its almost wholly tropical African distribution is divided into two disjunct portions, with the smaller western segment restricted to a relatively small area of south-western Angola and northern Kaokoland. The diagnostic characters of the group are discussed, eight new taxa are described and one new combination made. A key to the western taxa is provided as well as a map showing their distribution.
Pax's Section Tetracanthae, with its circumscription modified to include only those species with single horizontally arranged cymes and included ovaries, comprises a most homogeneous group of plants characterised by numerous "good" morphological characters, and it is considered that the species included under the above most apt epithet form a very natural group.
Its distribution is almost entirely tropical and is divided into two disjunct portions; that on the eastern side of Africa is by far the larger, both in number of species and its area of distribution, which extends south of the tropic to about 27° 30' S. The western portion, with which this paper is concerned, is restricted, with relatively few species, to the south-west of Angola and northern Kaokoland, between 10° 30' S and 18° 30' S and lies ± 1.200 km to the west of the most westerly known representatives of the eastern segment of the distribution.
Although so widely separated geographically the two groups are obviously closely related and the similarities far too close and too numerous to be due to convergence. This close relationship is particularly evident between populations of E. subsalsa s.l. and those of robust plants of the E. schinzii affinity which occur along the Limpopo valley.
Plants belonging in this section are shrubby in habit, mostly of dwarf to medium height (usually less than 1 m), generally with 4-angled, more or less parallel-sided branches, with the characteristic 2 pairs of spines borne on more or less narrowly cuneate, usually decurrent, seldom continuous, horny shields. The axillary inflorescence comprises a cyme of three horizontally arranged cyathia (exceptions are restricted to the addition of one or two axially disposed cyathia), with an included ovary, an obtusely 3-lobed scarcely exserted capsule and more or less ovoid or ellipsoid (seldom subglobose) verrucose seeds; epidermal characters include randomly orientated, scattered paracytic stomata and straight-sided, mostly pentagonal epidermal cells.
In the area under consideration eight species are now recognised. Of these E. coerulans and E. subsalsa were previously published, E. subsalsa var. kaokoensis is raised to specific rank and five new species and three infra-specific taxa are now described. [...]