Heterostemon

Taxonomy

Heterostemon R.L. Desfontaines Mém. Mus. Hist. Nat. 4: 248. t. 12. 1818.

Subfamily: Caesalpinioideae.
Phylogenetic Number: 1.4.53.
Tribe: Detarieae.
Group: Brownea.
Species Studied - Species in Genus: 5 studied; 7 in genus.

Description

Fruit: A legume; unilocular; 9–19.5 cm long; 3–4.5 cm wide; 0.8–1.2 cm thick; 2–9 times longer than wide; with deciduous androecial sheath; with deciduous corolla; with deciduous calyx; without orifice formed by curving of fruit or fruit segments; straight to curved; not plicate; not twisted; symmetrical, or asymmetrical; oblong, or oblanceolate; with 1 straight and 1 curved suture; widest near middle or D-shaped, or widest near apex; not inflated; flattened; without beak; long tapered at apex; aligned with longitudinal axis of fruit; straight or rounded at base; aligned with longitudinal axis of fruit; with the apex and base uniform in texture; ligneous; seed chambers externally invisible; margin not constricted; margin without sulcus; margin plain; wing(s) absent; stipitate; with the stipe 6–10 mm long; with all layers dehiscing; splitting along suture(s). Dehiscence of valves along both sutures (initially along ventral); active; with valves separately breaking, or enrolling. Replum invisible. Epicarp dull; monochrome; dark reddish brown to reddish brown; with surface texture uniform; glabrous to pubescent and indurate (with golden hairs); with hairs erect; eglandular; without spines; not smooth; with elevated features; veined; transversely veined relative to fruit length; not tuberculate; rugose; not exfoliating (but often separating from mesocarp); without cracks; without embedded tissue, much thicker than epicarp, running from base to apex. Mesocarp present; surface not veined; 1-layered; without balsamic vesicles; without fibers; without reniform canals; solid; ligneous. Endocarp present; visible; dull; opaque; monochrome; reddish brown; without adhering pieces of testa; subseptate to nonseptate; not exfoliating; remaining fused to mesocarp and epicarp; entire. Seed(s) 2–12; length transverse to fruit length; neither overlapping nor touching; in 1 series. Funiculus 0.1–1 mm long; of 1 length only; thick; straight. Aril absent.

Seed: 20–25 mm long; 11–20 mm wide; 2–5 mm thick; not overgrown; not angular; symmetrical; ovate; flattened; with surface grooved (over embryonic axis); oblique; without visible radicle and cotyledon lobes; without hilar sinus; without umbo on seed faces; without medial ridge on each face. Cuticle not exfoliating; not inflated; not wrinkled. Testa present; without pieces of adhering epicarp; not adhering to endocarp; free from endocarp; dull; not modified by a bloom; colored; monochrome; dark to reddish brown; glabrous; smooth, or not smooth; with elevated features and recessed features; rugose and reticulate; coriaceous (subcoriaceous). Pleurogram absent. Pseudopleurogram absent. Fracture lines absent. Rim absent. Wing(s) absent. Raphe not visible. Hilum present; fully concealed; concealed by funicular remnant; without faboid split; larger than punctiform; 0.1–1.5 mm long; with curved outline; elliptic; apical at apex of radicle tip; raised; not within corona, halo, or rim. Lens not discernible. Endosperm absent. Cotyledons smooth; both outer faces convex; both the same thickness; both more or less of equal length; not folded; margin entire 180 degrees from base of radicle; similar at apex; completely concealing radicle, or partially concealing radicle (only tip exposed); notched at radicle and split over radicle; with the interface division terminating at base of radicle; without margins recessed; inner face flat; glabrous on inner face. Embryonic axis straight; parallel to length of seed to oblique to length of seed; without a joint evident between the radicle and the cotyledons. Radicle differentiated from cotyledon; centered between cotyledons. Plumule rudimentary; glabrous.

Distribution

Tropical America (Mainly Amazonia).

New World; Tropical United States to South America (mainly Amazonia); Brazil and Ecuador.

Tribal Notes

Tribe Detarieae

Bruneau et al. (2000) carried out extensive phylogenetic analyses of tribes Amherstieae and Detarieae. They concluded that they form a single monophyletic group. Therefore, they supported Polhill's (1995a, 1995b) decision to unite the two tribes.
 
 Fruit and seed:  H. cauliflorus  Pittier - top enrolled valve; H. conjugatus R. Spruce ex G. Bentham - center seed in situ;  H. ingifolius  Sandwith - bottom fruit.
Fruit and seed: H. cauliflorus Pittier - top enrolled valve; H. conjugatus R. Spruce ex G. Bentham - center seed in situ; H. ingifolius Sandwith - bottom fruit.
 Seed, cotyledon, embryo, and testa:  H. conjugatus  R. Spruce ex G. Bentham - top left center seed topography;  H. mimosoides  R.L. Desfontaines - far left cotyledon notched and split and concealing radicle (above) and embryonic axis (below), bottom left center seeds, testa SEMs.
Seed, cotyledon, embryo, and testa: H. conjugatus R. Spruce ex G. Bentham - top left center seed topography; H. mimosoides R.L. Desfontaines - far left cotyledon notched and split and concealing radicle (above) and embryonic axis (below), bottom left center seeds, testa SEMs.