HYDROCHOREA

Unarmed trees and arborescent shrubs commonly 5-27 m, some precociously fertile when smaller, the young stems and foliage gray- or brown-pilosulous, the lfts nearly always conspicuously bicolored, the inflorescence of umbelliform units of dimorphic flowers mostly axillary to coeval or distally to hyster-anthous lvs, the meristem continuous beyond them, in one species (of uncertain affinity) appearing terminally paniculate; phyllotaxy spiral. Stipules linear or subulate, caducous, perhaps sometimes 0. Lf-formula i—vii/3—35; petiolar nectary between or close below insertion of first or only pinna-pair, either sessile or stipitate (rarely suppressed), the head variably plane, convex or shallow-cupular; lft-pulvinules ±0.5-2.5 mm; venation of lfts pinnate. Peduncles 2-11 (-14) cm; fls compactly racemose-capitulate, the axis including pedestal 1.5-6 mm, the peripheral fls slenderly pedicellate, mostly 5-merous, the 1-4 distal fls sessile or shortly stoutly pedicellate, 5-8-merous; calyx campanulate or turbinate-campanulate (1-)1.4-7mm, corolla (2.6—)3—11 (— 12) mm; androecium of peripheral fls 10-24(-36)-merous, 11-43 mm; ovary truncate at apex, 8-12-ovulate. Pods (that of H. acreana unknown) often several per capitulum, stiffly erect-ascending, sessile or shortly pseudostipitate, in profile linear or broad-linear, straight or almost so, compressed but low-biconvex over each seed and depressed between them, the valves leathery or sublignescent, the mature fruit lomentiform (4.5-)5-12.5 x 0.75-1.9 cm, readily breaking horizontally between seeds and less readily so through the shallowly undulate sutures into square or transversely oblong, 1- seeded articles closed at each end by half of the interseminal septum; seeds hard, brown, areolate, the pleurogram complete. — Spp. 4, widespread in riparian habitats in the Orinoco and Amazon basins and in the Guianas, in Brazil extending E to Maranhão and S to the Pantanal in Mato Grosso do Sul.