Monographs Details: Chloroleucon
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.
Discussion:IX. CHLOROLEUCON (Bentham) Britton & Rose

Chloroleucon (Bentham) Britton & Rose, N. Amer. Fl. 23: 36. 1928. Pithecolobium sect. Chloroleucon Bentham, London J. Bot. 3: 197, 221, 1844. — Lectogeneritypus (Britton & Rose, 1928,1. c.): Ch. vincentis (Bentham) Britton & Rose = Pithecolobium vincentis Bentham = Chloroleucon mangense var. vincentis (Bentham) Barneby & Grimes.

Chloroleucum (Bentham) Britton & Rose ex Record, Trop. Woods 10: 24. 1927, sine descriptione generica. — Following Index Nominum Genericorum this antedates Chloroleucon Britton & Rose and is typified by Ch. guatamalense, a then newly described taxon obviously long posterior to the basionymic section Chloroleucon Bentham. Record merely provided a description for a plant that had been identified by Britton & Rose as a new species of the then undescribed genus Chloroleucon and misspelled the name.

Cathormion sensu Pittier, Arb. Legum. 1: 54-56. 1927; non Hasskarl, 1855.

Trees and shrubs adapted to an annual dry season, the lvs then partly or wholly deciduous, the annual growth differentiated into long- and short-shoots, long-shoots floriferous only their first year, the annotinous branches stiffly flexuous, lenticellate, randomly armed with solitary or paired, axillary thorns derived from lignescent sterile peduncles (but some branches, or some rare individual plants, unarmed), the flowering branchlets rapidly emergent from a cone of imbricate, striately nerved, caducous perules, the flowers at anthesis seldom coeval with mature lvs; indumentum of plain, forwardly curved hairs, sometimes lacking, never glandular. Stipules most commonly lacking, when present subulate, filiform, linear, or oblanceolate-elliptic, quickly deciduous. Lf-formula i-ix/1-46, the subsessile lfts linear to obovate, the size and outline reciprocally adjusted to number; petiolar nectary concave, sessile or almost so, usually near or below midpetiole, rarely between first (or only) pair of pinnae, smaller nectaries at tip of lf-stk and pinna- rachises. Peduncles either solitary or fasciculate at 1-4 lower, foliate or efoliate nodes of brachyblasts, surpassed by mature lvs, ebracteolate; fls mostly ascending, either capitate or densely shortly racemose-spicate, the receptacle usually obovate, sometimes linear-fusiform, or obovate and produced into terminal pedestal of a heteromorphic fl; bracts very small, usually deciduous before anthesis; flowers of each unit of inflorescence either homomorphic or commonly dimorphic, the always sessile terminal one then a little stouter and with modified androecium; perianth normally 5-merous (random exceptions); calyx narrowly campanulate, 5-nerved, short-toothed; corolla narrowly tubular with dilated limb, the tube striately nerved when dry; androecium 10-30-, in Ch. chacoense to 52-merous, the tube weakly united at base to corolla, in peripheral fls included to distinctly exserted, in terminal fls always exserted, strongly dilated at orifice and there randomly fimbriate by auxiliary sterile filaments; ovary sessile, either conic or truncate at apex; style a little longer or shorter than filaments, the stigma minutely dilated. Pods sessile but sometimes basally attenuate, linear or narrow- oblong either straight, or backwardly falcate, or coiled into a compressed or open helix, or erratically decurved and twisted, the sutures either evenly decurved or undulately constricted between seeds, the valves when ripe either ligneous or coriaceous (thinly so in Ch. chacoense), coarsely venulose; dehiscence tardy and inert, through one or both sutures, but these seldom gaping widely enough to release the seeds, the valves in age sometimes cracking horizontally between seeds; endocarp not colored, coherent between successive seeds but seldom produced there as incipient septa; funicle filiform, sinuous; seeds either transverse (in wider pods) or basipetal (in narrower ones), compressed-lenticular, with hard pallid testa and finely engraved, often incomplete pleurogram; endosperm 0. — Spp. 10 (1 pluriracial), of lowland and less often submontane, xeromorphic brush-woodlands, seasonally dry forests, savannas, and deserts in warm-temperate and tropical America, from NW Mexico (27°N) to the Antilles, Argentina (28°S) and SE Brazil, in equatorial latitudes found mostly in savanna enclaves within forest climax. Fl. at onset of rainy season(s), in desert following erratic rains.

The genus Chloroleucon was first described by Bentham as a section of Pithecolobium, and, even with later additions that have expanded its boundaries, it remains firmly characterized by axillary spines, striate resting-buds, and proteranthous capitula. The spines are modified sterile peduncles, such as occur in no other Ingeae. They have been carelessly interpreted (Mohlenbrock, 1963: 439; Nielsen, 1981: 182) as spinescent stipules, such as occur in Pithecellobium sens. str. and Havardia, but are identified by axillary origin and by occasional rudimentary flower-buds at tip. The flowers of each capitulum are nearly always heteromorphic (either one or several distal ones larger than rest, with modified androecium), which we take to indicate relationship to Albizia, as already suggested by Nielsen (1981). Buds with striate perules that protect the primordia of floriferous branchlets or long-shoots are found also in the seemingly related genus Leucochloron, but this differs in absence of spines and in a characteristic membranous seed-coat lacking pleurogram. The fruits of Chloroleucon are variable in texture and extremely diverse in curvature, passing from almost straight to falcate or turned into a flattened spiral. The fruit is sometimes necessary for certain identification to species.

It must be borne in mind that some herbarium specimens do not show the armature of spines, and M. Nee informs us that in Bolivia some whole trees of Ch. mangense var. mathewsii are spineless. Unarmed flowering specimens of Ch. guantanamense from Hispaniola (Garcia 4837, NY) came from trees armed on the trunk with thorny efoliate branchlets. Also some capitula seem to lack a heteromorphic flower, but we have seen few of these, and some specimens in young leaf do not retain the deciduous perules. These cannot be referred by formula (or by our key) to their genus, and will readily be recognized as Chloroleucon only by close students of Ingeae.

Cassens and Miller (1981) distinguished the wood of Chloroleucon from other taxa that lacked septate fibers and confluent parenchyma on the basis of the color of the heartwood and the specific gravity. Chloroleucon dumosum is unlike other members of the genus they examined in having biseriate, not uniseriate rays.