Cojoba Britton & Rose, N. Amer. Fl. 23: 29. 1928. — Generitypus: C. arborea (Linnaeus) Britton & Rose = Mimosa arborea Linnaeus. — Pithecellobium sect. Cojoba (Britton & Rose) Mohlenbrock, Reinwardtia 6: 446. 1963.
Pithecolobium sect. Samanea ser. Carnosae [sic] Bentham, Trans. Linn. Soc. London 30: 587, magna ex parte (spp. 65, 67, 69, typica exclusa).
Obolinga Barneby, Brittonia 41: 170. 1989. — Sp. unica, C. zanonii (Barneby) Barneby & Grimes = Obolinga zanonii Barneby.
Cojoba sensu Britton & Killip, 1936: 127; Nielsen, 1981: 188.
Unarmed trees and arborescent shrubs, either micro- or macrophyllidious, with lenticellate branchlets. Indumentum of brown or sordid hairs. Stipules always small, often ephemeral or obsolescent, persistent in C. filipes, lignescent in C. bahorucensis and randomly so in C. zanonii. Lvs mostly bipinnate, the lf-formula i-xxii/2-50, often intraspecifically labile, in C. rufescens simply paripinnate, the lfts then 1-9- jug.; lf-nectaries sessile, cupular thick-rimmed, on lf-stks at or close below pinna-pairs, exceptionally 1-2 on petiole proper, and in some species smaller nectaries on some distal interfoliolar segments of pinna- rachises or between some or all leaflet-pairs; venation of lfts basically palmate and pinnate, but essentially pinnate in C. rufescens and indistinct in some others. Inflorescence of capitula arising either singly or fasciculate and contemporaneously or sequentially from the axil of coeval or newly shed lvs, or at efoliate nodes of annotinous branchlets, the capitula spherical, the fls radiating in all directions from subglobose receptacle (perhaps not in C. bahorucensis); fls sessile (the calyx sometimes contracted at base into an obscure solid pseudopedicel), the 5-merous perianth greenish-white somewhat fragrant, glabrous externally except for tip of calyx-teeth and corolla-lobes, or sometimes (C. escuintlensis) uniformly pale-brown puberulent, the campanulate or deeply campanulate, 5-nerved or almost nerveless tube very shortly toothed and commonly only 1/3- as long as the slenderly tubular or very narrowly trumpet-shaped corolla; androecium 20—66-merous, the tube nearly half as long as, nearly as long as, or shortly exceeding corolla, neither callous nor nectariferous internally; ovary (sub)sessile, linear-ellipsoid, at anthesis glabrous; ovules mostly 10-15 (some often abortive); style a little longer than androecium, the stigma poriform. Pod more or less pendulous, in most species linear or broad-linear in profile and simply retrofalcate or randomly contorted, scarcely or deeply constricted between seeds, sometimes with narrow and elongate interseminal isthmi (then moniliform), or in C. bahorucensis, C. filipes, and C. zanonii the pod plumply cylindric terete, the sutures immersed, the valves in any case fleshy and glossy red (brown-red, deep pink) when fresh, after dehiscence withering brown, leathery and crumpled, the endocarp smooth tan internally; dehiscence through one or both sutures, either on the tree, or less often on the ground, the valves crumpling and contracting to expose the seeds; seed-funicle straight or simply bent, subfiliform and wiry, or narrowly dilated and stiff after dehiscence; seeds in the indehisced pod of most species basipetal, mutually discrete along the cavity, and plumply ellipsoid to subglobose, in C. bahorucensis, C. filipes, and C. zanonii obese, contiguous along cavity and distorted by mutual pressure, the testa in all closely investing the plump, white or greenish embryo, black or dark brown becoming brittle, and somewhat wrinkled, lacking pleurogram.
Spp. 12, most of them adapted to wet lowland or submontane evergreen tropical forest, but three West Indian ones to semideciduous lowland brush-wood- land or chaparral; four species native in Greater Antilles, 4 in NW Andean and trans-Andean South America, the remainder in SE Mexico and Central America, one (C. arborea) nearly coextensive with the genus. — Etymology: cojoba, a vernacular name for C. arborea in Puerto Rico.
Our concept of the genus Cojoba is coextensive with that of Britton & Rose, but expanded to admit the peripheral C. filipes, misplaced by Britton & Rose in Samanea, and the recently described Obolinga zanonii.
The genus Cojoba is defined primarily by fruit and seed characters. It differs from related Zygia in inflorescence architecture, the peduncles being axillary or feebly ramiflorous and not, as in almost all zygias, cauliflorous. In the rare cases where this distinction fails, the flower of Zygia has an intrastaminal disc, whereas that of Cojoba lacks it. Furthermore all Cojobae (? bahorucensis) have flowers radiating in all directions from a dense capitulum; in Zygia the unit-inflorescences are either spicate, or when capituloid, the flowers are acroscopic. Some cojobas when in flower only may be confounded with Abarema but differ in lack of a modified terminal flower. Furthermore, no Abarema has flowers radiating in all directions from the capitulum; all are at least somewhat ascending. The one (pluriracial) species of Cojoba with simply pinnate leaves differs from Inga in the dehiscent pod, and is in every other aspect typical of its genus.
Cassens and Miller (1981) reported that the wood of Cojoba is unique among the New World Ingeae they examined in having minute vessel pitting. Miller (1989) noted that the wood of C. zanonii shares the same feature.