Subfamily: Faboideae.
Phylogenetic Number: 3.10.38.
Tribe: Phaseoleae.
Subtribe: Glycininae.
Species Studied - Species in Genus: 2 studied; 2 in genus.
Fruit: A legume; unilocular; 8–14 cm long; 2.4–3 cm wide; 0.3–0.4 cm thick; 2–9 times longer than wide; with deciduous androecial sheath; with deciduous corolla; with persistent calyx; with calyx shorter than fruit; without orifice formed by curving of fruit or fruit segments; straight; not plicate; not twisted; asymmetrical; falcate, or linear; with both sutures parallelly curved, or both sutures nearly straight; not inflated; flattened; with beak (short); declined; with solid beak the same color and texture as fruit; rounded at apex; aligned with longitudinal axis of fruit; rounded at base to tapered at base; aligned with longitudinal axis of fruit to oblique with longitudinal axis of fruit (slightly); with the apex and base uniform in texture; chartaceous, or fragile, thinner than chartaceous, like Trifolium; seed chambers externally visible; margin not constricted; margin without sulcus; margin embellished; margin with wing(s); wing(s) present; wing(s) 1, or 2; wing(s) 1–2 mm wide; wing(s) sutural; wing(s) on 1 suture, or both sutures; nonstipitate; indehiscent. Replum invisible. Epicarp glossy; monochrome; drying dark brown to black, or black to yellow to green ((black to reddish yellow to green) in life lighter); with surface texture uniform; glabrous; eglandular; without spines; not smooth; with elevated features; not veined; not tuberculate; wrinkled; exfoliating in part, or not exfoliating; with cracks; cracking transverse to fruit length; without embedded tissue, much thicker than epicarp, running from base to apex. Mesocarp present; trace; surface not veined; 1-layered; without balsamic vesicles; without fibers; without reniform canals; solid; chartaceous. Endocarp present; visible; glossy; opaque; streaked; brown; with various shades brown overlay; smooth; without adhering pieces of testa; subseptate; with septa thicker than paper, firm; with septa eglandular; chartaceous; not exfoliating; remaining fused to mesocarp and epicarp; with wing(s) extending into epicarp; entire. Seed(s) 5–20; length transverse to fruit length; neither overlapping nor touching; in 1 series. Funiculus 5 mm long; of 1 length only; filiform; contorted. Aril present; dry; when dry rim-aril and tongue-aril; fimbriate; tan.
Seed: 6.3 mm long; 3.4 mm wide; 1.5 mm thick; not overgrown; not angular; asymmetrical; reniform; compressed; 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; dull; not modified by a bloom; colored; monochrome; dark reddish brown; glabrous; smooth; coriaceous. Pleurogram absent. Pseudopleurogram absent. Fracture lines absent. Rim absent. Wing(s) absent. Raphe not visible. Hilum present; partially concealed; concealed by aril; with faboid split; with the lips of the faboid split the same color as the rest of the hilum; larger than punctiform; 1 mm long; with curved outline; circular; marginal according to radicle tip; recessed; not within corona, halo, or rim. Lens discernible; 1 mm long; with margins straight; linear; not in groove of raphe; confluent with hilum; flush; similar color as testa; darker than testa; within halo; halo color darker than testa. 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; partially concealing radicle; split over radicle; without lobes; with the interface division terminating at base of radicle; without margins recessed; brown; inner face flat; glabrous on inner face. Embryonic axis straight; perpendicular to length of seed; without a joint evident between the radicle and the cotyledons. Radicle differentiated from cotyledon; linear; lobe tip curved; oblique to cotyledons; centered between cotyledons; less than 1/2 length of cotyledons. Plumule rudimentary; glabrous.
Lackey (1981) noted that Mastersia resembles Shuteria (10.41), "especially in its seeds."Welzen and Hengst (1984) monographed Mastersia. Only one immature seed was studied internally.