Desmanthus leptolobus can be readily differentiated from most other Desmanthus species.
Some of the many features that may aid in the recognition of D. leptolobus:
The underside of the leaflets are smooth rather than hairy (when magnified).
While all other species of Desmanthus, including D. illinoensis, possess ovoid buds, D. leptolobus has distinctly elongated and slightly pointed buds.
The heads are consistently composed entirely of perfect flowers and do not show the presence of either male or sterile flowers. This character is found sporadically in D. virgatus and more frequently in D. illinoensis.
Its flower petals are linear instead of lanceolate.
D. leptolobus has 5 stamens rather than 10. (Characteristic also of D. illinoensis and the Baja endemic D. oligospermus)
The fruits and seeds of D. leptolobus are distinct from the rest of the genus:
Pods show slight and regular constrictions between seeds.
Divisions between seeds are set transversely rather than at an angle (obliquely).
The valves have scalloped edges, caused by the regular constrictions between the seeds and dehiscence initially beginning next to each seed.
The seeds are placed longitudinally within the pods.
The seeds are far longer and narrower than any other Desmanthus species. This is the only one that produces such elongated seeds
The pleurogram on each seed is quite large, deep and consistently asymmetrical.
D. illinoensis is the closest relative to D. leptolobus.
Both have 5 stamens, the general absence of male and sterile flowers, similar appearing foliage with many pinnae and numerous leaflets, and "very long setiform stipules with reduced auricles".
The stipules in D. illinoensis have a winged margin at their base; a feature lacking in D. leptolobus.
The erect to semi-erect D. illinoensis is easily distinguished from the prostrate to decumbent D. leptolobus.
D. illinoensis has more flowers per head than D. leptolobus and more seed pods per head.
In contrast to the long and linear pods of D. leptolobus, those of D. illinoensis are short and curved.
[See our references for a taxonomic description of D. illinoensis]
The roots of D. leptolobus tend to be less gnarled, much straighter and thinner than D. illinoensis.
Compared to the often robustly branching D. illinoensis roots, those of D. leptolobus show only a relatively few thin branches.
However, the proportion of rootbark relative to the rootwood is higher in D. leptolobus than in D. illinoensis.
D. virgatus var. depressus also grows prostrate but is easily differentiated by having larger leaflets, 10 stamens rather than 5, male and sterile flowers may be present, its seeds are flattened and ovate, and they are placed in the pods obliquely rather than lengthwise.
The divisions between its seeds are diagonal to edge of pod.
D. cooleyi (Cooley's Desmanthus) occurs farther west, has smaller stipules (2 mm or less in length) and rhombic seeds.
Desmanthus cooleyi is most closely related to, and often confused with, D. velutinus.
Both have pink staminodia and filaments, very reduced bracts in the head that never extend past the young buds, elongated leathery legumes that twist after dehiscence, raised rugulate-papillate seed coats and pinnae that move downward at night.
Unlike D. velutinus, D. cooleyi does not ever have pubescence on the underside of the leaf surface, has fewer pinnae, shorter peduncles, and usually has more than a single flower head per axil on at least some stems.
Desmanthus cooleyi usually has wider fruit, larger glands on the petioles, shorter peduncles and very small, deciduous stipules.
Note: while D. velutinus has highly variable pubescence, 3 glabrous collections are known.
(LUCKOW 1993; STUBBENDIECK & CONARD 1989; TROUT)