Gelrebia E. Gagnon & G. P. Lewis, 2016

Gagnon, Edeline, Bruneau, Anne, Hughes, Colin E., de Queiroz, Luciano Paganucci & Lewis, Gwilym P., 2016, A new generic system for the pantropical Caesalpinia group (Leguminosae), PhytoKeys 71, pp. 1-160 : 35-37

9. Gelrebia E. Gagnon & G. P. Lewis gen. nov. Figs 11J , 16

Diagnosis.

Gelrebia is morphologically similar to Caesalpinia s. s. but the two genera differ somewhat in habit, with Gelrebia species being erect to scrambling shrubs (vs. erect shrubs or small trees), in having dark pinkish mauve to light pinkish-white flowers (vs. flowers that are variable in colour, from yellow, white, red and orange to green), and coriaceous, broadly oblong-ovoid to obliquely pyriform pods, with a large, oblique, rounded base (vs. coriaceous, oblong-elliptic to linear pods, with an oblique cuneate base).

Type.

Gelrebia rubra (Engl.) E. Gagnon & G. P. Lewis ≡ Hoffmannseggia rubra Engl.: Caesalpinia rubra (Engl.) Brenan

Description.

Erect to scambling shrubs, 0.3-5 m tall, armed with scattered, straight or curved, deflexed prickles (these 7-20 mm long); stems puberulous to pubescent when young, glabrescent. Stipules not seen. Leaves alternate, bipinnate, ending in a pair of pinnae; pinnae opposite, in 1-17 pairs; leaflets opposite (except in Gelrebia glandulosopedicellata ), in 1-33 pairs per pinna, narrowly oblong or oblong-elliptic, 3-11 × 2-5 mm, apex rounded to emarginate, sometimes mucronate, glabrous or sparsely pubescent, lower surface of the blades with numerous subepidermal glands or translucent dots (best seen with a × 10 hand lens or microscope). Inflorescence a terminal or axillary raceme, c. (1-) 2-19 (- 25) cm long, unarmed; bracts broadly ovate to suborbicular, apex aristate, 3-10 mm long, caducous. Flowers bisexual, zygomorphic; calyx comprising a short hypanthium with 5 sepals, c. 5-13 mm long, eglandular, glabrous to finely pubescent, lower sepal strongly cucullate (occasionally with a beaked apex), covering the other 4 sepals in bud before anthesis, all sepals caducous, but hypanthium persisting as a free ring around the pedicel as the pod matures; petals 5, free, dark pinkish mauve to light pinkish-white, c. 7-24 × 5-15 mm, eglandular; stamens 10, free, filaments 8-20 mm long, pubescent and eglandular; ovary glabrous. Fruit a coriaceous, broadly oblong-ovoid to obliquely pyriform pod, apex acute, with a large, oblique, rounded base, c. 15-40 × 12-23 mm, dehiscent along both sutures, glabrous to minutely pubescent, eglandular. Seeds obovoid, laterally compressed.

Geographic distribution.

A genus of nine taxa in eight species, restricted to Africa, in Namibia, Botswana, South Africa, Northern Kenya, Ethiopia, and Somalia. One species also found in the Democratic Republic of the Congo (Zaire, Katanga).

Habitat.

Deciduous bushland, dry woodlands, on rocky ridges, often along dry river beds, or on sandy valley floors. One species also found in degraded savanna, close to termite mounds.

Etymology.

Gelreb or gelrib is the Somali name for Gelrebia trothae subsp. erlangeri (field labels of Dale K724 ( “gelrib”) and of Gillett 13223 ( “gelreb”) from Kenya), meaning 'camel trap’ and clearly alluding to the robust deflexed prickles characteristic of the species, and indeed the genus as a whole, which can hinder the passage of camels.

References.

Wilczek (1951); Roti-Michelozzi (1957); Brenan (1963, 1967); Ross (1977: 122-130); Thulin (1980, 1983: 16-18; 1993: 344-347); Germishuizen (1991); Roux (2003); Curtis and Mannheimer (2005: 226-228); Brummitt et al. (2007).

Figures

Figure 11. Caesalpinia bahamensis Lam. A inflorescence D fruits (G. P. Lewis, Cuba, Lewis 1853 (K )). Caesalpinia nipensis Urb. B flowers E fruits (G. P. Lewis, Cuba, Lewis 1838 (K )). Caesalpinia cassioides Willd. C inflorescence (C. E. Hughes, Ancash, Peru, Hughes et al. 2228 (K )). Caesalpinia pulcherrima L. (Sw.) F inflorescence (C. E. Hughes, Sonora, Mexico, unvouchered); Denisophytum pauciflorum (Griseb.) E. Gagnon & G. P. Lewis G flower and leaves (G. P. Lewis, Cuba, Lewis 1854 (K )) H branch with spine-tipped woody protuberances (B. Torke, Cuba, Torke et al. 1424 (NY )). Denisophytum madagascariense R. Vig. I flowers and fruits (G. P. Lewis, Madagascar, Lewis et al. 2158 (K )). Gelrebia trothae (Harms) E. Gagnon & G. P. Lewis J inflorescence (P. J. Cribb, Tanzania, unvouchered).

Figure 16. Gelrebia trothae E. Gagnon & G. P. Lewis subsp. trothae. A part of branch showing inflorescence with flowers and fruits B portion of leaflet margin, lower surface C longitudinal section of flower D median petal inner surface E lateral petal inner surface F stamen G anther H ovary with part of wall removed to expose ovules I fruit valve after dehiscence J seed. Gelrebia trothae subsp. erlangeri (Harms) E. Gagnon & G. P. Lewis K part of inflorescence L fruit. A-H from Milne-Redhead & Taylor 11177 I, J from Ward U 27 K from Gillett 13223 L from Hemming 478. Drawn by L. M. Ripley, originally published in F. T. E. A., Leguminosae subfamily Caesalpinioideae, page 34, fig. 5 (1967).