Hesperothamnus

Taxonomy

Hesperothamnus T.S. Brandegee Univ. Calif. Publ. Bot. 6: 499. 1919.

Subfamily: Faboideae.
Phylogenetic Number: 3.7.
Tribe: Millettieae.
Species Studied - Species in Genus: 2 studied; ca. 5 in genus.

Description

Fruit: A legume; unilocular; 5–10 cm long; 0.6–1.7 cm wide; 0.3–0.6 cm thick; 2–9 times longer than wide; with deciduous androecial sheath; with deciduous corolla; with deciduous calyx, or persistent calyx; with calyx shorter than fruit; without orifice formed by curving of fruit or fruit segments; straight; not plicate; not twisted; symmetrical, or asymmetrical; linear to moniliform, or falcate (slightly); with both sutures parallelly curved; not inflated; compressed; with beak, or without beak; straight; with solid beak the same color and texture as fruit; tapered at apex; aligned with longitudinal axis of fruit, or oblique with longitudinal axis of fruit; tapered at base; aligned with longitudinal axis of fruit; with the apex and base uniform in texture; coriaceous; seed chambers externally visible; seed chambers with the raised seed chambers not torulose; margin constricted; margin constricted along both margins; margin without sulcus; margin embellished; margin with thickened sutural areas; wing(s) absent; nonstipitate; with all layers dehiscing; splitting along suture(s). Dehiscence of valves along both sutures; apical and down; active; with valves twisting. Replum invisible. Epicarp dull; monochrome; tan to green; with surface texture uniform; pubescent and indurate; with hairs appressed; with 1 type of pubescence; sericeous to tomentose; with pubescence golden, or white; with simple hairs; pliable; with hair bases plain; eglandular; without spines; not smooth; with elevated features; veined, or not veined; reticulately veined; not tuberculate; wrinkled; not exfoliating; without cracks; without embedded tissue, much thicker than epicarp, running from base to apex. Mesocarp present; thin; surface not veined; 1-layered, or 2-layered; without balsamic vesicles; without fibers; without reniform canals; solid; with solid layer over solid layer; coriaceous. Endocarp present; visible; dull; opaque, or translucent; monochrome; green, or white; smooth and scurfy, or cracked and scurfy; without adhering pieces of testa; nonseptate; chartaceous; exfoliating in part, or not exfoliating; separating from mesocarp; without wings; entire. Seed(s) 2–4; length parallel with fruit length, or oblique to fruit length; neither overlapping nor touching; in 1 series. Funiculus 1–2.5 mm long; of 1 length only; thick; contorted. Aril present; dry; when dry rim-aril and tongue-aril; entire; creamy yellow.

Seed: Ca. 11 mm long; 7–9 mm wide; 3–3.5 mm thick; not overgrown; not angular; symmetrical; elliptic; 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; brown; glabrous; smooth, or not smooth; with elevated features; lightly rugose; chartaceous. Pleurogram absent. Pseudopleurogram absent. Fracture lines absent. Rim absent. Wing(s) absent. Raphe not visible. Hilum present; partially concealed; concealed by funicular remnant; with faboid split; with the lips of the faboid split the same color as the rest of the hilum; larger than punctiform; ca. 1.8 mm long; with curved outline; oval; recessed; within rim; rim color of testa. 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; not concealing radicle; entire 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 deflexed; oblique to length of seed; with a joint evident between the radicle and the cotyledons. Radicle differentiated from cotyledon; linear; lobe tip straight; oblique to cotyledons; centered between cotyledons; less than 1/2 length of cotyledons. Plumule rudimentary; glabrous.

Distribution

Mexico.

New World; Mexico.

Generic Notes

This genus was included in Millettia by Geesink (1984). Because Geesink did not make any combinations for the species in Millettia, nor has there been a recent treatment of the group, we have recognized the genus. Only one whole, mature seed was seen.

Tribal Notes

Tribe Millettieae

Geesink (1981) treated this tribe, as others before him, under the tribal name Tephroseae, but we now know that its correct name is Millettieae. Recent tribal studies (Geesink, 1981, 1984; Polhill, 1994a, 1994b) have arranged the genera in alphabetical order without phylogenetic numbers. Geesink (1984) monographed tribe Millettieae, and presented descriptive notes about fruits and seeds and in situ fruit and seed drawings. However, we are not entirely following Geesink (1984) for generic parameters because he either questioned the status of many of his new genera or did not make the necessary species transfers. The few new genera which he clearly recognized are being accepted. Lavin et al. (1998) developed a preliminary infratribal classification of six informal groups using phytochrome nucleotides: Millettia group, Lonchocarpus group, Derris group, Tephrosia group, "primitive" group, and Phaseoleae group. Lavin (1987) transferred Sphinctospermum to Millettieae. Lavin and Doyle (1991) carried out cladistic analyses integrating morphological and chloroplast DNA data, and concluded that it is a member of Robineae where we have placed it (now 8.12).