Monographs Details: Abarema
Authors:Rupert C. Barneby
Authority: 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.
Scientific Name:Abarema Pittier


Abarema Pittier, Arb. Legum. 1: 56. 1927, based on Pithecolobium sect. Abaremotemon Bentham in Hooker, London J. Bot. 3: 203. 1844. - Sp. lectotypica (Britton & Killip, Ann. New York Acad. Sci. 35: 126. 1936): P. auaremotemo Martius = Abarema cochliacarpos (Gomes) Grimes & Barneby.-The subsequently proposed lectotypus (Cowan, Taxon 8: 58. 1959) is rejected. Cowan believed the type of Abarema should be among the species listed by Pittier and chose A. trapezifolia as the better known. The genus was based, however, on sect. Abaremotemon Bentham, of which P. auaremotemo is the unavoidable lectotypus.

Pithecolobium sect. Samanea ser. Axillares Bentham in Hooker, London J. Bot. 3: 216, ex parte (spp. no. 55-57 omissis). 1844. - Sp. lectotypica, one of few in which Bentham knew the dehiscent pod: P. rhombeum Bentham = Abarema brachystachya (de Candolle) Barneby & Grimes.

Pithecolobium sect. Gyrolobium Grisebach, Fl. Brit. W. I. 226. 1860, ex parte, exclus. P.filicifolio. - Sp. lectotypica: P. micradenium Bentham = Abarema jupunba (Willdenow) Britton & Killip var. jupunba.

Jupunba Britton & Rose, N. Amer. Fl. 23: 25. 1928. - Sp. typica: J. jupunba (Willdenow) Britton & Rose = Acacia jupunba Willdenow = Pithecellobium jupunba (Willdenow) Urban = Abarema jupunba (Willdenow) Barneby & Grimes.

Punjuba Britton & Rose, N. Amer. Fl. 23: 28. 1928. - Sp. typica: P. racemiflora (Donnell Smith) Britton & Rose = Pithecellobium racemiflorum Donnell Smith = Abarema racemiflora (Donnell Smith) Barneby & Grimes. Klugiodendron Britton & Killip, Ann. New York Acad. Sci. 35: 125, 1936. - Sp. typica: K. laetum (Poeppig & Endlicher) Britton & Killip = Abarema laeta (Poeppig & Endlicher) Barneby & Grimes.

Pithecolobium sect. Abaremotemo [sic] sensu Bentham, 1875: 581; 1876: 43 ("Abaremotemon").

Pithecolobium sect. Clypearia sensu Mohlenbrock, 1963: 446, ex parte, typo exclus. 1963; Punjuba sensu Nielsen, 1981: 190.

Unarmed trees, some flowering first as bushy treelets but few remaining shrubby when adult. Growth monopodial (not confirmed in all species), the shoots monomorphic; phyllotaxy spiral. Indumentum of simple hairs, usually brown, tawny, or bronze, dense on young branchlets and on axillary buds, often thin or deciduous in age, the lfts often glabrous on upper face, but the inflorescence always at least thinly puberulent. Stipules commonly small, narrow, caducous long before maturity of the associated lf, sometimes 0; no imbricate bud-scales. Lvs bipinnate, the pairs of pinnae and lfts one to many, the lft size and number reciprocally adjusted; one nectary on lf-stks almost always between or close below proximal pair of pinna-pulvinules, often one smaller one between further pairs, and nearly always between furthest pairs of lfts, none elsewhere on plant, the nectaries campanulate to cupular, patel- liform, or verruciform, only rarely stipitate, sometimes immersed; venation of lfts primarily pinnate, the secondary veins always brochidodrome within the margin and often giving rise to a tertiary or quaternary reticulum. Inflorescence of spikes, racemes, or capitula, these axillary to coeval or rarely to hysteranthous or rudimentary lvs, the whole inflorescence when efoliate a pseudoraceme or short panicle (no cauliflory); fls bracteate in vernation, ebracteolate, the bracts nearly always caducous; the fls of any unit of inflorescence either homomorphic or dimorphic, the 1-few distal fls sessile and longer, or no longer but stouter, than the peripheral ones, and their androecium often thicker, with more numerous filaments united into a longer tube, this dimorphic fl expanding either before or with the rest; perianth with random exceptions 5-merous, the calyx campanulate or turbinate-campanulate, the often unequal teeth broader than long, the corolla narrowly funnelform, its lobes ascending; androecium 10-60- merous, the filaments united into a tube either shorter or longer than the corolla and the tube itself adherent to the corolla to form a short stemonozone; ovary either fusiform or truncate distally; style usually exserted from among longer stamens, not or scarcely dilated at apex; ovules (6-)8-14(-16). Pods sessile but sometimes backwardly attenuate at base, long-persistent after dehiscence, in profile broad-linear, falcately or spirally recurved (or equivalently contorted), the coarse sutures framing valves that are at first plane but in varying degree thickened at maturity and elevated over each seed, the ventral suture commonly undulate or in some species deeply recessed between seeds, the valves themselves varying from stiffly papery to leathery or ligneous, the always-thin exocarp either smooth or papillate and often coarsely venulose, the endocarp, as revealed on dehiscence, most often red, crimson, orange, or castaneous (especially in the cup-shaped seed-cavities) but often pale tan between seeds; dehiscence elastic, downward through both sutures but more readily and sometimes exclusively through the seminiferous (convex) outer one, the valves both vertically recurved and horizontally twisted but the torsion inhibited in some pods of extremely thick texture; seeds transverse or obliquely basipetal, following dehiscence suspended on a strap-shaped funicle sigmoidally bent distally, plumply lentiform or somewhat compressed, the testa thin, sometimes partly white opaque but otherwise translucent, colorless or becoming yellowish brownish in age, in texture resembling a grape-skin, girdled by a simple nerve, either closely or loosely investing the embryo, in some species charged on each face with finely engraved, elliptic or almost round pleurogram, but in others not so; endosperm 0; cotyledons horny, planoconvex, closely appressed by their flat side, convex externally and there either aniline-blue or fuscous, their color transmitted through the translucent parts of the seed-coat; plumule concealed by the cotyledons. Seedlings seen from few species, producing an onion- or garliclike odor upon germination, cotyledons epigeal, sessile, auriculate at base; eophylls opposite, bipinnate. - Spp. 44, endemic to the New World tropics, but one extending N to warm- temperate Bahamas and two S along the coast of E Brazil to Paraná and Sta Catarina, most numerous in the Amazon basin and on the Guayana Highland, but secondarily developed in the Greater Antilles, Central America, and Atlantic Brazil.

The genus Abarema, first formulated by Bentham as a section of Pithecolobium in 1844, has now grown so large that it can no longer be easily defined in exact terms. Its constant features are: (a) unarmed stems; (b) inflorescence composed of axillary peduncles, either solitary or fasciculate but never assembled into efoliate pseudoracemes, and borne on an auxotelic primary axis; (c) pinnately veined leaflets; and (d) a fruit that in dehiscence exposes seeds with lustrous, white or variably colored but never black seed-coat against a background of red or red-brown endocarp. Ornithochary is the established method of seed dispersal. The embryo is nearly always aniline-blue due to the presence of delphinidin (B. Meurer-Grimes, unpubl. data), and this may be synapomorphic. In a few instances, the embryo is described as gray or brown. However, it is not yet determined in these cases if this is the mature condition. Observations on various species (e.g., A. jupunba, A. curvicarpa, A. mataybifolia, and others) in the field show that the seeds do not attain the blue color until well near dehiscence; seeds in indehisced pods are often brown, and seeds that fail to germinate quickly lose the blue color. Likewise seeds damaged by predation or pathogens often lack coloration. In any case, even if the seeds are brown or gray at maturity, the cladistic analysis indicates that the brown condition represents a loss of delphinidin and not the pleisiomorphic condition.

The analysis further shows that Abarema is monophyletic on the basis of five synapomorphies: the lentiform seeds (no. 37) persistent on funicles (no. 38) against a background of red or red-brown endocarp (no. 33), the blue embryo (no. 43), and the geotropic pods (no. 45). All but the blue embryo are homoplastic in the context of the whole of Ingeae. The red or red-brown endocarp and seeds persistent on the funicle are found again in Archidendron and Pithecellobium sensu stricto; and the geotropic pods are found in almost all other members of the tribe.

The genus Cojoba resembles Abarema in organization of the inflorescence and auxotelic meristems, but has fleshy, red, not dry papery, leathery or lignescent valves of the pod, and seeds with black seed-coat. The slenderly tubular corolla of Cojoba, several times longer than the small campanulate calyx, is further distinctive, more like that of Chloroleucon than that of Abarema. Pithecellobium, as now defined, may have a fruit similar in texture and dehiscence to that of Abarema, but it differs not only in inflorescence architecture but also in arillate seeds and (with one exception) randomly armed stems. Hydrochorea and

Balizia share with Abarema the indeterminate inflorescence of axillary peduncles and differ materially only in their fruits and seeds, as described in our key to major American taxa of Ingeae (p. 13).

Features common but not universal (except perhaps the anthocyanic embryo, not recorded in a few species) are: (a) brown or golden pubescence of nascent stems and leaf buds; (b) shortly racemose, cymose, or capitate units of inflorescence terminating in a dimorphic flower; (c) white filaments; and (d) pods strongly decurved or backwardly coiled into a compressed spiral and elastically dehiscent through both sutures. The leaf-formula and leaflet-size vary widely between species, the ovary may be either truncate or conical at apex, dehiscence of the pod, depending on texture of the valves, may be either bivalvar or follicular, and the seeds may be areolate or not. With the possible exception of A. levelii, the fruit of which is not yet known, there is no species of Abarema doubtfully referred to the genus or any that is in any real sense ambiguous between Abarema and another genus.

The genus Klugiodendron has lately been recognized by Nielsen (1981) as a genus of indefinite scope related to Abarema and Cojoba. Mohlenbrock (1963) subordinated it to Pithecellobium, with the false attribute of arillate seeds. The myth of an arillate seed can be traced back to Poeppig’s descriptions of Inga laeta and Pithecolobium polycarpum, the latter based on fruiting specimens said to have seeds with smooth blue testa and a short white fleshy aril at the base, which we interpret as the crumpled funicle. Poeppig’s two species were synonymized by Bentham and the so-called aril of P. polycarpum was carried over into the description of P. laetum, and thence into that of Klugiodendron.