Acrocarpus

Taxonomy

Acrocarpus R. Wight & G.A.W. Arnott Mag. Zool. Bot. 2: 547. 1838.

Subfamily: Caesalpinioideae.
Phylogenetic Number: 1.1.03.
Tribe: Caesalpinieae.
Group: Acrocarpus.
Species Studied - Species in Genus: 1 studied; 1 in genus.

Description

Fruit: A legume; unilocular; 7–17 cm long; 1.2–2 cm wide; 0.2–0.3 cm thick; 2–9 times longer than wide to more than 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; not plicate; not twisted; symmetrical; lanceolate, or linear to oblong; not inflated; flattened; without beak; long tapered at apex; aligned with longitudinal axis of fruit; long tapered at base; aligned with longitudinal axis of fruit; with the apex and base uniform in texture; coriaceous; seed chambers externally visible; margin constricted, or not constricted; margin slightly constricted along both margins ("margins"); margin without sulcus; margin embellished; margin with wing(s); wing(s) present; wing(s) 1; wing(s) 0.1–5 mm wide; wing(s) sutural; wing(s) on 1 suture; stipitate; with the stipe 6–15 mm long; with all layers dehiscing; splitting along suture(s). Dehiscence of valves along both sutures; apical and down; passive. Replum invisible. Epicarp dull to glossy; monochrome; dark brown to black; with surface texture uniform; glabrous; eglandular; without spines; not smooth; with elevated features; not veined; not tuberculate; usually pusticulate; exfoliating; with cracks; cracking longitudinal to fruit length; 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; coriaceous. Endocarp present; visible; dull; opaque; monochrome; brown to tan; without adhering pieces of testa; subseptate; not exfoliating; remaining fused to mesocarp and epicarp; entire. Seed(s) 5–18; length oblique to fruit length to transverse to fruit length; neither overlapping nor touching; in 1 series. Funiculus 0.1–2 mm long; of 1 length only; thick; S-curved. Aril absent.

Seed: 6.5–7 mm long; 4.2–4.5 mm wide; 2 mm thick; not overgrown; not angular; symmetrical; ovate, or elliptic, or circular; flattened; with surface smooth; 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; glossy to dull; not modified by a bloom; colored; brown; glabrous; smooth; osseous. Pleurogram absent. Pseudopleurogram absent. Fracture lines present; concentric. Rim absent. Wing(s) absent. Raphe not visible. Hilum present; fully concealed; concealed by funicular remnant; without faboid split; larger than punctiform; 0.1–3 mm long; with curved outline; elliptic; subapical to radicle tip; flush; not within corona, halo, or rim. Lens not discernible. Endosperm present; thick; not pluglike and not resembling tip of radicle; adnate to embryo. 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; partially concealing radicle; with lobes; with lobes not touching; 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; without a joint evident between the radicle and the cotyledons. Radicle differentiated from cotyledon; centered between cotyledons. Plumule rudimentary; glabrous.

Distribution

India to Thailand and Sumatra.

Old World; India, China, Indochina, and Indonesia and the Philippines (Sumatra).

Generic Notes

Generic Notes: Polhill and Vidal (1981) described seeds of the monogeneric Acrocarpus group as having "a small loosely adherent aril," and Watson and Dallwitz (1983) described seeds as "arillate (small)." The seeds are nonarillate, because the so-called aril is an indurate (albeit prominent) funiculus. A legume aril is an overgrown modification of a funiculus or parts of a funiculus. Watson and Dallwitz erroneously reported seeds to be "sometimes winged." Because A. combretiflorus Teijsman & Binnendijk is conspecific with A. fraxinifolius, there is only one species in the genus, not two as reported by Polhill and Vidal. Fruit and seed characters of A. combretiflorus from the protolog and syntype (Teysman, s.n., sheet number 908.3–1008, L) are included in this description.