Abarema commutata
Rupert C. Barneby
12. Abarema commutata Barneby & Grimes, sp. nov., cum A. villifera (Ducke) Barneby & Grimes hucusque confusa et ei certe affinis, sed ab ea pinnis foliolisque magis numerosis (folii cujusque majoris 52, nec 16-20), pinnarum distalium rachi longiori (4-12 nec 2.5-4.5 cm usque longa), capitulorum axi longiori (4-10, nec 2-3 cm longo), necnon flosculis periphericis majoribus (calyce 4.5-6, nec 3-4.2 mm longo), ulterius patria in regione altiori Guayanae diversum. — GUYANA. Southern Pakaraima Mts: Waipa trail from north Kopinang Savanna, 2750 ft, 4.IX.1961 (fl.), B. Maguire (with C. K. Maguire & G. Wilson-Browne) 46100. — Holotypus, NY; isotypus, UC 221602!, US.
Round-headed macrophyllidious trees 8-20 m, the young stems and all axes of lvs and inflorescence densely villous-tomentulose with brown-golden or bronze hairs 0.2-0.8 mm, the bark at length glabrate and blackish mottled, the foliage bicolored, the coriaceous lfts dark-green (when dry brown) glabrous and lustrous above, paler and densely golden-brown-villous beneath, the loose capitula of white fls borne singly and paired in the axil of coevally expanding lvs, early immersed in foliage. Stipules early caducous (few seen), elliptic-oblanceolate 3.5-6.5 x 0.8-1.3 mm. Lf-formula (i—)ii—iv/3—6; lf-stks stout (1—)2.5—15 cm, the petiole (0.5-)0.8-2.4 cm, the one (or longest) interpinnal segment 0.5-4-(-5) cm; petiolar nectary close below first pair of pinnae sessile, low-convex dimpled or almost plane 1.2-2.6 mm diam, smaller ones random on distal segments of lf-stk and on 1-3 furthest segments of pinnae; pinnae much accrescent distally, the rachis of the furthest pair (3—)4—10(—12) cm, the longer interfoliolar segments 10-24 mm; paraphyllidia linear-lanceolate 0.7-2 mm; lft-pulvinules 1-2 x 0.9-1.8 mm; lfts strongly accrescent distally, in outline obovate-elliptic, rhombic-elliptic or obtusely rhombic from inequilaterally cuneate base, broadly obtuse, the distal pair (3-)3.5-6.5 x 2.1-4.5 cm, 1.4-2 times as long as wide; the scarcely displaced, gently incurved midrib giving rise on each side to 8-12 major (and random weak intercalary) secondary nerves brochidodrome within the strongly revolute margin, these simple or rarely branched, only in Surinam proliferating into a mesh of raised veinlets. Peduncles 3.5-8 cm; capitula ±12—22-fld, the axis including terminal pedestal 4—9 mm; bracts elliptic-oblanceolate 2.5-4 x 1-1.5 mm, caducous; fls white, dimorphic, the lower peripheral ones raised on a pedicel 0.5-1.2 mm, the terminal fl sessile, the 5-merous perianth of all densely silky externally; PERIPHERAL FLS: calyx turbinate-campanulate 4.5-6 x 3.3-4.5 mm, the ovate-triangular teeth 1.3-2.3 mm; corolla ±9-10 mm, the lobes erect; androecium 26-36-merous, to 25-36 mm, the stemonozone 0.8-1.8 mm, the tube 3-5 mm; ovary subsessile, ellipsoid, densely pubescent; TERMINAL FL: calyx broadly campanulate 5-7 mm; corolla 8-10 mm; stamen-tube 8-12 mm, the stamens to 40. Pods (one seen, this perhaps stunted and atypical) sessile, narrowly oblong in profile, recurved through less than ¼-circle, piano-compressed but low-convex over each of ±8 seeds, the valves crustaceous, framed by sutures ±2 mm wide, glabrescent, dull brown outside, reddish overall within; dehiscence through both sutures, the valves coiling; seeds not seen.
In savanna-forest ecotone and in openings in scrub forest, 825-1200 m, localized on the E edge of the Guayana Highland: Gran Sabana in SE state of Bolívar, Venezuela; Pakaraima and Kanuku mts in W- centr. Guyana; and on Tafelberg, Surinam. — Map 14.— Fl. VIII-IX. — Ercey-euru-yek (Venezuela; the bark yields saponins for washing).
Since Maguire 24629 (NY) from Table Mountain in Surinam was identified by Amshoff (in the 1940s) as Pithecellobium villiferum, all subsequent collections have been so named in herbaria. The species is obviously close to A. villifera in habit, indumentum, and broad obovate or rhombic-obovate leaflets, but differs in dispersal, habitat, average leaf-formula, looser capitula, and larger peripheral flowers, as noted in our diagnosis and key to species. It seems therefore to deserve specific status.
All our material from Venezuela and Guyana has leaflets essentially veinless on the convex upper face and pinnately veined with 8-12 prominent major pairs of almost simple secondary nerves on the dorsal face, in this respect resembling typical A. villifera from the upper Río Negro basin. The one collection from Surinam has smaller leaves and secondary nerves prominulous on both faces and moreover branched into a mesh of veinlets, a venation recalling the variant of A. villifera described from Río Cueiras in the lower Río Negro basin. Whether these poorly documented variants are individual variants or have a genetic basis remains to be seen.
References: [Article] Barneby, Rupert C. & Grimes, James W. 1996. Silk tree, guanacaste, monkey's earring: a generic system for the synandrous Mimosaceae of the Americas. Part I. Abarema, Albizia, and allies. Mem. New York Bot. Gard. 74: 1-292.