Euphorbia cuneata in East and Northeast Tropical Africa

Abstract

Euphorbia cuneata Vahl is a woody much-branched shrub of the small subgenus Lyciopsis (Boiss.) Wheeler, to 3 or even 4 m high, with bark which peels off in papery flakes. The horizontally spreading, spine-tipped branchlets bear shortly petiolate, cuneate-spathulate leaves to about 3 cm long, alternate on young growth, or more usually tufted on very short axillary shoots. These shoots also produce the terminal cymes which are sometimes simple but usually consist of 4 or more cyathia. The species was first described as a glabrous, woody shrub by Vahl, in 1791, from a non-annotated specimen in Forsskal's Arabian collection. In 1847 Edgeworth described a woody shrub with puberulous branches and leaves from Aden, as E. fruticosa. This Aden form was also described from a collection by Perrottet and given the name E. perrottetii by Jaubert and Spach, in 1855, who distinguished it from the Yemen species principally by its pubescent leaves. Anderson, in 1860, recognized Edgeworth's E.fruticosa as synonymous with E. cuneata and stated that young growths and leaves of the species were sometimes pubescent. He was evidently unaware that this Aden form had also been given the name of E. perrottetii. Boissier however, in 1862, upheld a distinction, but at varietal level under E. cuneata, the only species in his section Lyciopsis. In addition he described a new variety, var. carpasus, citing one specimen from Eritrea (Ehrenberg) and a second from Zanzibar (Boivin). It differed by its thinner, reddish (instead of grey) stems and non-fasciculated leaves. However, in 1867 Schweinfurth considered the Eritrean form to be identical to the species which he treated as Lyciopsis cuneata, a new genus not upheld by other authors and which he had also dropped by 1899. In 1894 Pax described a new related species, E. spinescens, based upon a specimen of Fischer's from Massaini, Tanzania, distinguishing it from E. cuneata by its single cyathia and completely glabrous nature. A year later he described another species, E. lyciopsis, also based upon a single specimen, this time collected by Volkens from tfear Lake Challa on the Tanzania-Kenya border. This differed from E. spinescens in the arrangement of the leaves, which were single, never fasciculate. It was not until 1911 that N. E. Brown, in his account of the genus Euphorbia for the Flora of Tropical Africa, recognized the variability of the northern forms and reduced all names to synonymy under E. cuneata. However, he upheld the southern species E. spinescens and E. lyciopsis,