Small decumbent, often prostrate, perennial herbs; woody at base.
They grow erect only when young.
The trailing stems are few to many; spreading to 100 cm (39 inches).
Mowed plants show much greater branching.
The taproot is 40 cm (16 inches) or more long (75-90 cm [2.5-3 feet] is common), 1-2 cm (0.4-0.8 inches) in diameter in adult plants, cylindrical, gently tapering, woody, sometimes gnarled, with gray-brown to reddish-brown, thick and corky bark.
Branches from taproot are relatively few and thin.
Young stems are angled, sometimes reddish, usually green with corky ridges, glabrous except for scattered minute hairs; older stems are more rounded in cross-section, red or brown, and glabrous.
Green stipules are setiform, glabrous and persistent, (2.5-)4-6(-7.0) mm long; their base lacks a winged margin.
Leaves are from 2.6-6.3 cm long, with a petiole 2 to 5 mm long, and a rachis from 13 to 37 mm long.
All are glabrous.
Pinnae occurs in 4-9(-10) pairs that are 15-22 mm long, the lowest pair may bear a stalkless, rounded, craterlike nectary from 0.3 to 0.6 mm in diameter.
The nectary is occasionally rudimentary or absent.
Leaflets are nearly stalkless, in 15 to 22 (-25) pairs, 2.0-4.5 (-6.8) mm long, 0.5-1.0 mm wide.
They are curved, narrowly elliptic to linear, rounded obliquely at their base, ending in a point or a short abrupt spike at their tip, glabrous except for appressed white hairs sparsely distributed along the margin.
With the exception of the excentric midvein; the venation is obscure.
Inflorescence: Flower heads are few, occur only 1 per leaf axil, and are borne on 0.6-2.0 cm long peduncles.
A bract subtends each flower.
Pale green bracts are from 0.6 to 1.6 mm long and 0.3-0.5 mm wide.
They are strongly 1-nerved, glabrous, deltate and membranous with an opaque midvein.
While most bracts are stalkless, sometimes a short pedicel is present.
Bracts are often scattered along the stem below the inflorescence.
Flower buds are elongated with a pointed tip (acute apex).
Flower heads are 0.4-0.6 cm long, each containing 4-10 perfect flowers, with sterile and male flowers entirely absent.
Perfect flowers possessing an obtriangular calyx from 1.7 to 3.3 mm long, the tube is from 1.2 to 2.9 mm long, and 1.15 to 1.80 mm in diameter.
Calyx is glabrous: rimmed with free, sharply pointed lobes that are 0.35-0.75 mm long, pale green or white, 5-nerved, thin and membranous between the nerves when dry;
The pale green or white petals are glabrous and linear, from 3.0 to 5.0 mm long, and 0.3 to 0.5 mm wide;
The 5 stamens, do not extend beyond the sepals, and are 1.8 to 2.8 mm long.
There are no glands on the anthers;
The linear, glabrous ovary is 0.7 to 1.25 mm long with a 1.4 to 2.5 mm style that extends beyond the stamens.
Fruit: Fruiting peduncles are 0.8-2.5 cm long; each bearing 1 to 9 pods.
The elongated thin legumes first split intermittently (in a wave) by each seed, initially only along the upper suture but then dehisce along both sutures; frequently the basalmost seed is retained longer than the rest.
Linear pods often curve slightly and are from (1.8-)4.0-7.4 cm long and 2.5-3.0 mm wide.
The thin and leathery valves are constricted between the seeds, the tip narrowing to form a 1-3 mm long beak; green, thin and flat if young, maturing reddish-brown, turning wrinkled and dark brown to almost black; gentle, short, lengthwise wrinkles form as they dry.
Seeds: (2-)4-10 per pod, 4.5-6.2 mm long, 1.9-2.3 mm wide, longitudinally inserted, oblong or narrowly obovate, flattened reddish-brown; pleurogram 0.4-0.7 mm wide, 2.8-4.1 mm deep, U-shaped, asymmetrical.
Flowering mostly in early Summer; May through July in Texas, July through August farther north.
[In 1998-2000 flowering began in April in Central Texas]
Fruiting through September.
In Central Texas, the fruit ripens during the last half of July and the first part of August.
Most seeds have been dispersed by mid-August.
(BENTHAM 1874; LUCKOW 1993; TROUT [personal observations]; TURNER 1959)