Monographs Details: Hydrochorea acreana (J.F.Macbr.) Barneby & J.W.Grimes
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.
Family:Mimosaceae
Description:Species Description - Macrophyllidious unarmed tree ±25-30 m, with smooth terete nonlenticellate homotinous branches, the lf-axes and the terminal, efoliate, broadly corymbose-paniculate inflorescence of umbelliform racemes finely densely brown-puberulent with incurved hairs not over 0.15 mm, the foliage strongly bicolored, the chartaceous, finely venulose lfts when dry lustrous brown above, olivaceous beneath, glabrous facially except for very sparsely pubescent midrib, microscopically ciliolate. Stipules 0 (or perhaps very early caducous, but no scars observed). Lf-formula iv-v/4-6; lf-stks stout 10-21 cm, the petiole 4-6.5 cm, at middle 2-3 mm diam, the interpinnal segments 2-5.5 cm, the wide shallow ventral groove interrupted at each pinna-pair by a nectary, the one near or above midpetiole sessile cupular elliptic 2-3 mm diam, 0.8-1 mm tall, distal ones on lf-stk and between 1-several distal lft-pairs progressively smaller; pinnae accrescent distally, the rachis of penultimate or furthest pair up to 9-15 cm, the interfoliolar segments 1.4-3 cm; pulvinule of lfts in dorsal view 1.3-2 x 0.7-1 mm, strongly wrinkled, puberulent; lfts accrescent distally, obtusely rhombic-ovate from inequilateral, broadly rounded base, very shortly or obscurely acuminate, obtuse at very apex, the largest ±3.5-6.2 x 1.6-3.7 cm, 1.7-1.8 times as long as wide; venation pinnate, the nearly centric, forwardly arched midrib giving rise to ±10-17 pairs of major and various minor, straight, widely ascending secondary nerves brochidodrome well within the revolute margin, and these in turn to a reticulum of venules, the whole venation prominulous on both faces but more sharply so beneath. Primary axis of inflorescence 7-18 cm, that of the lowest branches ±5-10 cm, the upper progressively shorter, all widely ascending, the peduncles crowded distally, together forming a broad-topped panicle; bracts subtending inflorescence- branches 1-3 mm, caducous; peduncles fasciculate by 2-3, 20-33 mm; racemes ±25-30-fld, the axis including pedestal of terminal fl 3-4 mm, shallowly pitted; bracts minute caducous; fls either homo- or dimorphic, the peripheral ones pedicellate, the terminal one, when present, sessile, with larger calyx, the perianth of all 5-merous, minutely puberulent externally, brown when dry; PERIPHERAL FLS: pedicels 2.5-5 x 0.3-0.5 mm; calyx narrowly campanulate ±2 x 0.8-1.2 mm, the deltate-triangular obtuse teeth 0.4 mm; corolla narrowly trumpet-shaped ±4 mm, the ovate, weakly 1-nerved lobes 1-1.2 x 0.7-0.8 mm; androecium 10-12-merous, the stemonozone ±1 mm, the tube 1.7-2 mm, the longer stamens 13-15.5 mm; ovary short-stipitate (±0.5 mm), glabrous, truncate at apex; style about as long as stamens, the slightly dilated stigma 0.1 mm wide at apex; TERMINAL FL: calyx including solid base 2.8-4.5 x 1.2-1.5 mm, the ovate-triangular teeth 0.7-0.8 mm; corolla tubular 7 mm, the ovate lobes 13-14 x 0.8-0.9 mm; androecium 10-merous, ±12 mm long, the leathery tube ±6.5 mm, the filaments grossly thickened at point of separation, attenuate distally, apparently ascending (not sigmoid). Pod unknown.

Distribution and Ecology - In non-inundated Amazonian forest, known certainly only from the Brazilian state of Acre (9°18'- 20'S, 69°-72°40'W). The paratype (Klug 3079) is here referred to Abarema adenophora. Suggestively similar is sterile material from Bolívar, Venezuela (C. Blanco 751 from Reserva Forestal La Paragua (VEN) and E. L. Little 17653 (VEN) from between El Palmar and Río Grande, 200 m [samán montañero acc. Blanco]), though slightly different in narrower ventral groove of lf-axes and lfts minutely silky- strigulose beneath. — Ingá fava.

Discussion:Hydrochorea acreana is known with certainty from only two flowering collections, which differs from other species of Hydrochorea in the panicle of capitula efoliate at anthesis; pending discovery of the fruit its affinity cannot be assessed with finality. The small peripheral flower with androecium reduced to 10 or 12 members is like that of some forms of the variable H. corymbosa, but the foliage, except for smaller petiolar nectaries, is more reminiscent of Abarema adenophora.
Distribution:Acre Brazil South America| BolĂ­var Venezuela South America|