Macrophyllidious arborescent shrubs and severaltrunked treelets 2-8 m, armed at all nodes or at all below the slender, pliantly flexuous branch-tips with a pair of widely ascending, straight, pungent lignescent stipules, the young branches and lf-axes either villosulous with fine spreading white hairs to 0.1-0.4 mm or subglabrous, the papery, moderately bicolored lfts either glabrous, or glabrous ciliolate, or pubescent beneath (sometimes with basal-posterior tuft) only, or pubescent on both faces, the lvs heteromorphic, the ampler lower ones (absent from some specimens) composed of more than 4 (but not more than 16) lfts, the small upper ones exactly 4-foliolate, the few-fld capitula solitary, arising either from the axil of primary lvs or (distally) from that of rudimentary lvs, then forming small, shortly exserted pseudoracemes. Stipules at least at some nodes of long-shoots 2-12 mm, tapering from dilated base, but at many distal or floriferous nodes shorter or reduced to a conic point or subulate spinule. Lf-formula i-ii/1-3, that of most distal lvs exactly i/1, the anterior 1ft of first pair of pluri-foliolate pinnae sometimes wanting; lf-stks (1.5-)2- 40 x 0.4-0.7 mm, openly shallow-sulcate ventrally, the one (or further of two) interfoliolar segment, when present, either a little longer or shorter than petiole proper; a comet- or trumpet-shaped, stipitate nectary 0.3-0.7 mm diam at tip of each lf-stk and each pinna- rachis, and often between each proximal pinna- or lft-pair; rachises of the one or the longer of 2 pinna-pairs (1.5-)2.5-30 mm, sometimes of slightly unequal length or vigor, when more than 2-foliolate the further interpinnal segment longest; lft-pulvinules 0.4-1.1 (-1.6) x 0.3-0.7 mm, weakly wrinkled; lfts variable according to position on branchlet, those of plurifoliolate pinnae strongly accrescent, those of primary lvs proportionately ampler than those of lvs associated with a peduncle, all broadly obovate or obovate- elliptic from inequilaterally cordate or semicordate base, at apex obtuse muticous, or obtuse mucronulate, or shallowly retuse, the distal pair 15-42 x 8-31 mm, 1.1-1.75 times as long as wide; venation pinnate, the only slightly excentric, straight or gently incurved and often subflexuous midrib giving rise on each side to  (3-)4-6 major (and few weak intercalary) secondary nerves brochidodrome well within the plane (obscurely undulate) margin, and these in turn to a variably developed 3-4-nary reticulum of veinlets, the whole venation at maturity usually prominulous on both faces, sometimes obscurely so on upper face. Peduncles very slender, the earlier ones 2-6.5 cm, some toward apex of some branchlets shorter; capitula 5—12(—13)-fld, the obovoid receptacle 1-2.5 mm (rarely one fl downwardly displaced onto peduncle); bracts triangular-ovate-acuminulate 0.4-0.7 mm, persistent; fls sessile homomorphic, the perianth 5- merous, externally either subglabrous or minutely silky-strigulose or -pilosulous overall, the corolla greenish or pinkish, the androecium white; calyx campanulate, submembranous faintly 5-nerved, 1.4-2.3 x 1-1.3 mm, the triangular teeth 0.1-0.3 mm; corolla narrowly trumpet-shaped 7.3-10 mm, the erect ovate lobes 1.4—2.6 x 0.9-1.3 mm; androecium (20-)24—32-merous, 18-23 mm, the stemonozone 0.6-1 mm, the tube 7-8.5 mm, nearly as long as or a trifle longer than corolla, internally at base thickened into low-convex callosities 0.4-0.5 mm; ovary linear- ellipsoid compressed 1.5-2.3 mm, contracted at base into a filiform stipe 2.6-4 mm, at anthesis glabrous, puberulent after fertilization. Pods l(-2) per capitulum, in profile undulately linear, evenly recurved through ±²/3-2 circles, 6.5-11 x 0.8-1.1 cm, 8-13 (-14)-seeded, contracted at base into a stipe 3-6 mm, abruptly acute at apex, laterally compressed but domed over each seed, the ventral (outer) suture usually a little constricted between seeds, the dorsal suture evenly decurved, but the body often also horizontally twisted and therefore not forming a flattened spiral, the stiffly papery valves at first dark red, fuscous red, or nearly black, red within, not septiferous; dehiscence elastic, through both sutures, the valves recurved and twisted, exposing the subpersistent seeds; funicle tapelike at base, distally dilated into a scalloped, red, pink, or whitish aril enveloping at least 1/3 of the seed; seeds descending, plumply lentiform ±6-8 x 5.5-6.5 x 3.5-5 mm, the crustaceous, lustrous black testa either smooth or minutely scrobiculate, closely investing the hard biconvex embryo, the nearly complete pleurogram ±4-6 mm diam.

In semideciduous thorn-scrub, thin woodland and cactus-chaparral, ranging from the upper limit of mangrove on the Pacific lowlands to 1250 m in arid inter-Andean valleys, flourishing in disturbed thickets, locally common in lowland SW Ecuador (Manabí, Guayas, El Oro) and NW Peru (Tumbes, Lam- bayeque), in Peru extending E to the Marañón valley in Cajamarca. - Map 1. — Fl nearly year-long, except when drought-inhibited, the new fls often coeval with old fruit. — Chaquero, uña de gata, uña de pava, zarcillo de mono.

Pithecellobium excelsum closely resembles P. unguis-cati, differing principally in the plurifoliolate leaves; the capitula are on the average fewer-flowered and the individual corolla is a trifle longer. It is the only Pithecellobium known to occur in Pacific Ecuador or northern Peru, and is seldom misidentified.