Euphorbia venteri L.C.Leach ex Archer & Carter (2001: 86

Bruyns, Peter V., Klak, Cornelia & Hanáček, Pavel, 2020, A review of the Euphorbia schinzii-complex (Euphorbiaceae) in southern Africa, Phytotaxa 436 (3), pp. 201-221 : 219-220

11. Euphorbia venteri L.C.Leach ex Archer & Carter (2001: 86 , t. 2176).

Type:— BOTSWANA. 2 km north of Tsamaya near Tsessebe, ± 45 km north of Francistown, 12 December 1991, Venter et al. 174 (holotype PRE!, isotypes K!, UNIN).

Discussion:— Euphorbia venteri was described from a single collection from north-eastern Botswana. It was said to differ from E. schinzii by the ‘thick and irregularly shaped root and more or less cylindrical branches’, while ‘ E. schinzii usually has rhizomatous roots with short, upright branches’. It was also compared with E. limpopoana , which was characterized as ‘much more robust forming a large clump to 2 m in diam. (lacking rhizomes) with very long and thick branches bearing prominent spines’. The branches of E. limpopoana and E. schinzii were said to be ‘conspicuously four-angled’. The ‘greenish to greenish brown glands’ of E. venteri also differed from the bright yellow glands of the cyathia in both E. limpopoana and E. schinzii ( Archer & Carter 2001) .

North of Francistown E. venteri is common between Tsesebe, Tutuma and Zwenhambe ( Fig. 11 ). The type plant and other plants seen around Tsesebe were small and compact, with rhizomatous branches running horizontally underground for up to 10 cm (then projecting above-ground for 2−10 cm) and spines 2−6 mm long. Others found near Zwenhambe were laxly branched in clumps to 0.3 m in diam., with branches to 20 cm long above the ground and spines up to 10 mm long. In these specimens there were no rhizomatous branches and they were difficult to distinguish from small plants of E. schinzii subsp. bechuanica . The branches are variable in cross-section, from 4-angled ( Fig. 1D ), to obscurely 4-angled, with the tubercles forming wedge-shaped pairs along the branch (as shown in the figure of the type in Archer & Carter, 2001, where they are not ‘cylindrical’ at all), to almost cylindrical. Consequently, although they may occur, ‘cylindrical branches’ are not typical of E. venteri (see also Fig. 1 D , where they are also not cylindrical). Since both E. schinzii and E. venteri may have rhizomatous branches, this feature also does not separate E. venteri from E. schinzii .

This species is distinguished from others in this complex by its pale grey-green, weakly 4-angled to almost cylindrical branches with paler markings between the angles, spine-shields slender below the spines and tapering to a fine point, as well as the dull yellowish green to brownish green cyathial glands that may be suffused with red towards their margins and the red anthers.

At present, this is the only species of Euphorbia that is endemic to Botswana. Since it occurs close to the NE border of the country, it may occur in adjacent parts of Zimbabwe. Its relationships to material recorded by White et al. (1941) and Leach (1991) from Bulawayo, Zimbabwe and to E. acervata from the Great Dyke in Zimbabwe remain unclear.

Additional specimens examined: — BOTSWANA. Tutuma (2027AC), 1070 m, Bruyns 12363 (MO). 2 km west of Zwenhambe (2027AD), 1270 m, Bruyns 12359 (BOL). Southern end of Tutuma (2027CA), 1150 m, Bruyns 12362 (NBG). 21 km west of Tsesebe (2027CB), 1200 m, Bruyns 12355 (UPS). 9 km west of Tsesebe (2027DA), 1200 m, Bruyns 12354 (S). Tsesebe (2027DC), 1180 m, Bruyns 12353 (BOL).

Figures

FIGURE 1. Tips of branches showing arrangement of tubercles and spine-shields with spines and stipular prickles. A–D, tubercles fused vertically into angles (though fusion of tubercles is the least in D), often with larger stipular prickles (largest inA and B and smallest in D) and spine-shields narrowly elliptic in A and B becoming more narrowly deltate in C and D, E–H, tubercles not fused vertically into angles, with minute stipular prickles and shortly deltate spine-shields, which are especially short in E and G. A, E. schinzii subsp. schinzii, Bruyns 9390 (BOL), ± 8 mm thick. B, E. schinzii subsp. bechuanica, Bruyns 12101 (BOL), ± 10 mm thick. C, E. schinzii subsp. schinzioides, Bruyns 12426 (BOL), ± 8 mm thick. D, E. venteri, Bruyns 12354 (BOL), ± 6 mm thick. E, E. clivicola subsp. clivicola, Bruyns 12115 (BOL), ± 10 mm thick. F, E. clivicola subsp. clivicola, Bruyns 11329 (BOL), ± 6 mm thick. G, E. clivicola subsp. clivicola, Bruyns 13556 (BOL), ± 8 mm thick. H, E. clivicola subsp. calcritica, Bruyns 12045 (BOL), ± 6 mm thick.

FIGURE 11. Distribution of Euphorbia venteri.