Mimosa albida Humb. & Bonpl. ex Willd.

Authors

Rupert C. Barneby

Authority

Barneby, Rupert C. 1991. Sensitivae Censitae. A description of the genus Mimosa Linnaeus (Mimosaceae) in the New World. Mem. New York Bot. Gard. 65: 1-835.

Family

Mimosaceae

Scientific Name

Mimosa albida Humb. & Bonpl. ex Willd.

Type

324. Mimosa albida Humboldt & Bonpland ex Willdenow, Sp. pl. 4: 1030. 1806.—Typus infra sub var. albida indicatur.

Description

Species Description - Diffuse, potentially frutescent herbs, bushy shrubs, weakly woody sarmentose vines and (rarely) treelets, sometimes flowering when only 5 dm tall but potentially attaining 3(-4) m, essentially like M. debilis except in the scabrous-strigose or glabrescent pod and prevailingly ovate-acuminate rather than obovate lfts (but lft-outline broadly randomly fallible), commonly armed on stems and petioles with scattered recurved aculei but sometimes erratically so and occasionally unarmed, the terete or striately nerved stems commonly at once setose or setulose and finely puberulent but either type of trichome at times lacking, the bicolored lfts most often either setose-strigose or both setose and puberulent on both faces, frequently either simply puberulent or glabrous above and setose-strigose beneath (the proximal lfts sometimes more densely so than distal ones), less often glabrous or glabrate on both faces, always discontinuously setose-ciliate. Stipules erect, lanceolate 2-7(-8) mm, the firm blade either glabrous or pubescent externally, l-3(-4)-nerved, coarsely setose-ciliate, persistent. Leaf-stalks 1.5-6.5(-8) cm; distal pair of lfts obliquely lance-elliptic or semi-ovate, exceptionally elliptic-obovate, from deeply semicordate base, often broadest near middle and acuminate or more abruptly acute and mucronate, the larger ones 25-80(-95) x 11-27(-37) mm, (1.9-)2-3.3 times as long as wide, the anterior lft of proximal pair subsymmetrically cordate to lanceolate, (2-)4-12 mm; secondary nerves from midrib either expiring or camptodrome within the margin. Peduncles (1—)2—5 per node, l-4(-4.7) cm; capitula usually globose, rarely ellipsoid, prior to anthesis moriform, without filaments 4.5-6.5(-7) mm diam.; bracts linear-oblanceolate 0.6-2 mm, either glabrous or puberulent dorsally, weakly or minutely ciliolate; flowers of M. debilis, the corolla-lobes puberulent or exceptionally glabrous except for minute granular cilia. Pods usually numerous per capitulum, either sessile or contracted at base into a true stipe or a stipelike neck 1-4 mm, the narrowly oblong body (8-)13-40(-43) x 4-8 mm, (l-)2- 5(-6)-seeded, the replum usually scabrous with forwardly subappressed setae less than 1 mm (commonly less than 0.5 mm), the valves in S. America similarly strigose and usually also puberulent, the strigae sparse to densely crowded, but the valves (in Mexico especially) sometimes merely puberulent or even quite glabrous.

Discussion

I here follow Rudd (1968) and Grether (1982) in circumscription of M. albida, except that I transfer var. aequatoriana Rudd to M. debilis, of which it has the densely hispid pod. Due to lack of fruiting material I have been unable to consider M. albida var. pochutlensis R. Grether, to which the same argument would apply in theory. If var. aequatoriana (and presumably var. pochutlensis) is maintained in M. albida, the circumscription of the latter must perforce be extended to accommodate the whole set of variations on the Sensitivae theme that I have assembled above under the title of M. debilis. When the spectrum of variation in habit, foliage, pubescence and inflorescence encompassed by M. debilis and M. albida is reviewed, the only practical division compatible with geographical dispersal is that proposed herein. I suspect that it is an artificial line arbitrarily drawn through a single polymorphic complex. It may be said that the leaflets of M. albida tend to be acuminate and broadest at or shortly below mid-blade, whereas those of M. debilis tend to be broader distally and abruptly acute or obtuse at apex; but there are numerous exceptions, recognized, for example, in Grether’s description of Mexican M. albida. Moreover elliptic leaflets occur in both species.

Rudd (1968), following and elaborating Robinson’s (1898) revision of M. albida, divided the species into varieties characterized by quality and dispersal of trichomes on leaves and pods, a practice which, if carried out evenhandedly through Mimosa, would vastly increase the number of infraspecific taxa without gain in exact definitions. McVaugh (1987: 203) has referred to the pubescence variants found in southwestern Mexico as "hardly more than forms," but I judge that they can usefully be sorted into two principal categories, corresponding with var. albida and var. glabrior as defined in the varietal key that follows, but no further divisible. Otherwise identical forms of M. albida with leaflets all setose on both faces, all setose beneath only, or some proximal leaflets setose but the distal ones not so (a pubescence pattern that recurs in M. debilis and in other subseries of ser. Mimosa) are sympatric over most of the range of the species. Grether’s map (1982: 82) vividly illustrates the sympatry of so-called vars. strigosa and albida in Mexico, and of vars. glabrior and euryphylla on the Pacific slope southward from middle Sinaloa; similarly random patterns of variation extend south along the Andes into Peru. Rudd de fined a var. willdenowii endemic to northern Venezuela by its supposedly "essentially glabrous" craspedium, but the density of strigae on the valves is in reality quite variable both inside and outside of the variety’s supposed range. The var. willdenowii is here reformulated to accommodate the Andean and Venezuelan races of M. albida with relatively wide pod, a feature that seems to be securely linked to dispersal.