Monographs Details: Desmanthus
Authority: Isley, Duane. 1973. Leguminosae of the United States: I. Subfamily. Mimosoideae. Mem. New York Bot. Gard. 25 (1): 1-152.
Description:Genus Description - Unarmed, often procumbent, perennial herbs or (rarely in U.S.) shrubs. Stems usually numerous from a woody caudex or swollen root. Leaves bipinnate- leafstalk gland(s) present, usually between or contiguous to lowermost pinnae, sometimes also between some other pairs; pinnae and leaflets few to many; leaflets of most species without secondary nervation. Stipules subulate to acicular, not evidently striate, usually persistent and evident. Inflorescences of solitary, axillary, often small and inconspicuous, whitish to greenish-white, infrequently pinkish heads. Flowers 5-numerous, perfect or the lowermost sterile with inconspicuous staminodes; calyx campanulate to short-cylindric, apically lobed; petals initially subconnate below, becoming separate; stamens 5-10, separate; ovary subsessile. Legume dehiscent, linear or broadly oblong and falcate, compressed, moderately constricted between the seeds or not; valves thinly to heavily coriaceous, at maturity separating along both sutures (dorsal often slightly first), not twisting. Seeds obliquely to longitudinally positioned in legume.
Perhaps 25 species primarily of warm or tropical America. U.S. representatives, except for D. illinoensis, limited to southern states, the major concentration in Texas.
CBN x — 14
Literature: Britton & Rose (1928), Turner, (1950a, 1950b, 1950c, 1959), Correll & Johnston (1970), Isely (1970a).
Desmanthus is one of those genera in which certain of the species complexes possess a bicentric distribution between the western United States (in this instance, Texas) and warm to temperate South America; e.g., the combination D. depressus var. acuminatus (Benth.) Burkart was rendered for Argentine material, but is based on a Texas type. A comparative study of the species of Desmanthus in the northern and southern hemispheres is underway at Southern Illinois University.
Several of us (Turner & Fearing, 1960b; Windier, 1966; Isely, 1970a) agree that Desmanthus and Neptunia represent closely allied lines of evolutionary specialization. Exomorphic similarities are supported by a common chromosome base number of 14, divergent from the usual x = 13 for the subfamily. But owing to the occasional presence of anther glands in Neptunia, the two genera are placed in separate tribes in the traditional mimosoid classification recently reiterated by Hutchison (1964).
Desmanthus—herbaceous, unarmed and with 5-10 stamens—is similar only to Neptunia. Desmanthus differs from Neptunia in the lack of foliar glands and striate-nerved stipules; in flower, Neptunia spikes are yellow to greenish-yellow; in fruit, Neptunia has stipitate legumes.
An exception to the above generalization is Mimosa strigillosa which is herbaceous and unarmed like Desmanthus and Neptunia, but has a segmented legume. In vegetative or flowering condition, the long (to 2 mm) bulbous-based hairs of the Mimosa and the leaf-rachis glands of Desmanthus constitute definitive markers.
First year regrowth sprouts of Leucaena leucocephala in Florida suggest a herbaceous species. The Leucaena is erect and robust; the only sympatric Desmanthus (D. virgatus var. depressus) is small and usually prostrate. D. covillei and D. virgatus var. glandulosus, the former local and rare in southern Arizona mountains, and the latter western Texas and slightly in Arizona, are suffrutescent to shrubby. They differ from associated Mimosa in being unarmed and in having leaf-rachis glands.