3. Zygia potaroensis Barneby & Grimes, sp. nov., Z. claviflorae affinis et stipulis paleaceis striatim nervulosis ei simillima, sed foliorum pinnis numerosis (8-9-, nec 4—6-jugis), foliolis minoribus (7.5-10, nec 11-18 mm usque longis) et praesertim legumine latiori, maturo septis interseminalibus perfectis praedito insigniter diversa. A Z. palustri, in Guyana proxime sympatrica, foliorum formula foliolisque dimidio vel ultra minoribus distantius videtur. — GUYANA: in forest along trail from Kaieteur Falls to Tukeit, 2.III.1962 (fr), R. S. Cowan &T. R. Soder- strom 2016. — Holotypus, NY; isotypus, K.
Slender microphyllidious, cauliflorous treelets 2-6 m tall, the young stems and all lf-axes densely pilosulous with erect yellow-brown hairs ±0.6-0.95 mm, the lvs bicolored, the thin-textured lfts olivaceous above, not brunnescent in drying, pallid beneath, glabrous. Stipules paleaceous lanceolate 6-15 x 1.2-2 mm, striately 9-13-nerved, persistent at tip of branchlets. Lf-formula viii—ix/15—19; lf-stks 8-15 cm, the petiole including poorly differentiated pulvinus 5-23 x 1-1.4 mm, the longer interpinnal segments 10-16 mm; nectary between or close below the proximal pinna-pair shallowly cupular thick-rimmed 1-1.8 mm diam, a similar, only slightly smaller one at tip of lf-stk, those on pinna-rachises minute or 0; pinnae proximally decrescent, the rachis of longer distal ones 4—6 cm, the longer interfoliolar segments to 2.5-3.5 mm; 1ft- pulvinules subobsolete, the blades sessile against rachis; lfts abruptly decrescent near base of rachis, slightly so distally, the blades asymmetrically oblong from obliquely truncate, postically acutangulate or incipiently auriculate base, a little incurved and at apex acutely triangular but not mucronate, the longer ones 7.5-10 x 2.4-3.5 mm, 2.6-3.1 times as long as wide; venation palmate and pinnate, delicately prominulous on both faces, the subcentric midrib incurved beyond middle, the inner posterior primary nerve produced well beyond midblade, the tertiary venules few and sinuous. Inflorescence not seen intact, and fls unknown. Pods pendulous, in profile broad-linear, nearly straight ±17-19 x 1-1.4 cm, plumply biconvex, ±9-11-seeded, the thinly leathery valves densely brownish-pilosulous overall, weakly venulose, the endocarp produced between seeds to form complete papery septa; dehiscence not seen; seeds vertically basipetal, plumply oblong-ellipsoid ±18 x 11 x 4.5 mm, the papery, fragile, dull brown testa loosely investing the homy embryo, girdled by a fine prominulous nerve, brittle when dry; pleurogram 0; endosperm 0.
In riparian rain forest, known only from the Kaieteur Plateau in Guyana and from headwaers of Río Caura in SW Bolívar, Venezuela. — Not mapped. — Fr. ripe in III-V.
Although the flowers of Z. potaroensis are lacking, we have no doubt of its relationship to Z. claviflora and Z. palustris, of which it has the pallid olivaceous foliage, striate paleaceous stipules, and cauliflory; and we have no scruple in describing it as new, on account of the fully septate pod, a remarkable feature formerly unknown in the group. In general aspect, Z. potaroensis appears nearest to Z. claviflora, which is remotely allopatric in southwestern Venezuela and northern Brazil and which differs substantially in leaf-formula (see diagnosis), in smaller leaflets, and in broader (though similarly pilosulous) pod. From Z. palustris, which Cowan and Soderstrom encountered on Kaieteur Plateau on the same day that they collected the type of Z. potaroensis, it differs not only in leaf-formula and size of leaflets but also in the plumply biconvex, densely pubescent, not planocompressed and facially glabrous fruit. We have contemplated the possibility that these two collections from Kaieteur represent lush flowering and modified fruiting specimens of one taxon, but the differences between them in foliage are altogether too great to support this view.