Mimosa distachya Cav.
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Authors
Rupert C. Barneby
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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.
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Family
Mimosaceae
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Scientific Name
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Type
31.Mimosa distachya Cavanilles, Icon. 3: 48. 1795.—Typus infra sub var. distachya indicatur.
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Description
Species Description - Drought-deciduous, potentially arborescent shrubs attaining 4 m, with pallid annotinous and flexuous terete, distantly or sparsely foliate young branches, either unarmed or randomly armed at or below nodes either with a solitary recurved, broad-based infrapetiolar aculeus 1-8 mm or occasionally also with 1-2 infrastipular ones, either glabrous throughout except for tomentulose axillary buds, or transiently puberulent, or finely silky-puberulent throughout, the foliage pale green or subglaucescent, the lfts either plane or (in one var.) incipiently revolute, the loose or relatively compact spikes or spiciform racemes borne either solitary or to 4 together in the axil of coevally expanding lvs, the whole inflorescence pseudoracemose only in praefloration. Stipules lance-subulate, linear-ligulate or setiform, (1-) 1.5-3.5 x 0.2-0.7 mm, 1-nerved or almost nerveless, becoming dry and fragile. Leafstalks (2-)2.5-10 cm, the petiole (0.7-)l-3.5 cm, the interpinnal segments up to 5-20(-26) mm, the ventral sulcus either continuous or occasionally bridged between pinna-pairs and minutely spiculate; pinnae 2-4(-5)-jug., the rachis of longer ones 6-35 mm; lfts 3-6(-7)-jug., subequilong or distally accrescent, in outline oblong, obovate, or oblance-elliptic, obtuse mucronulate or apiculate, the larger ones 3.5-17 x 2-11 mm, 1.5-3 times as long as wide, all dorsally (2-)3-4-nerved from pulvinule, the midrib slightly or considerably displaced, simple or pinnately 1-3- branched on each side, the inner posterior nerve expiring or brochidodrome beyond mid-blade, the outer ones much shorter. Spikes or racemes 4.5-6.5 mm diam. without filaments, the peduncle and floral axis together (1.5-)2-9 cm, the pyriform fl-buds either glabrous or thinly puberulent, the minute bracts caducous; pedicels at anthesis 0-0.8 mm (in fruit sometimes to 1.2 mm); flowers 5-merous 10-androus, all bisexual; calyx membranous, openly campanulate or turbinate-campanulate 0.4-1.4 mm, the rim either truncate or denticulate, the deltate teeth 0.1-0.3 mm; corolla turbinately vase-shaped 2.1-3 mm, the 1-nerved lobes ascending or at length recurved, 0.9-1.5 mm; filaments either white or pale pink, united at very base into a stemonozone, exserted 3-6 mm; ovary either glabrous or minutely puberulent laterally, sometimes becoming densely puberulent after fertilization. Pods to 15 per spike but commonly fewer, either stipitate or sessile, the stipe attaining 7 mm, the broad-linear, gently recurved body (13-) 17-60 x 5-8.5 m, (2-)3-9(-l l)-seeded, the replum either undulately constricted between seeds or nearly straight, either smooth unarmed or hispidly setose, the papery green, later stramineous valves prominently umbonate or low-bullate over each seed, delicately venulose, either glabrous overall, or glabrous and minutely granular, or puberulent overall, and in addition often hispid with erect setaculei to 1—1.5(—2) mm, when ripe breaking up into free-falling, at length individually dehiscent articles 4-8 mm long.
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Discussion
As here interpreted, M. distachya is a polymorphic species of bicentric dispersal, in desert and seasonally drought-stressed brush-woodland, about the western shores of the Caribbean and on the Pacific slope in Mexico, where it extends to Baja California and northward through the Sonoran Desert into southwestern Arizona. It is very closely related to the also polymorphic M. polyantha, which is mostly vicariant in upland interior southern Mexico, but sympatric with M. distachya in Sinaloa. Mimosa polyantha scarcely differs from M. distachya except in more numerous and smaller leafets, and is equally variable in indumentum of the pod, while fewer and larger leaflets, reduced to one or exceptionally two pairs per pinna, alone distinguish the also closely related M. rosei. Specimens (Purpus 3179, NY) ambiguous between M. polyantha and M. distachya have been collected on the Puebla-Oaxaca boundary, and these populations (left unclassified herein), which may perhaps include the type of M. brevispicata Britton, require close scrutiny in the field.
Four varieties of M. distachya are defined below. The var. oligacantha, distinguished principally by stout infrapetiolar aculei arising immediately below each node and not downwardly displaced onto the intemode, is geographically detached. Its leaves are finely pubescent except sometimes ventrally, its flowers are sessile, and its short-stipitate pod is both puberulent and remotely or randomly hispid with a few erect setaculei. The vars. distachya and laxiflora are geographically vicariant along the coastal plain and foothills of western Mexico and morphologically confluent. Collectively they may have either glabrous or puberulent foliage, either sessile or pedicellate flowers, and pods either glabrous or puberulent and in addition (independently) either hispidly setose or not. The var. laxiflora is arbitrarily set off by a combination of glabrous foliage, racemose flowers, smooth pod, and dispersal within the Sonoran Desert east and north of the Gulf of California. The variation in the residue is discussed briefly under var. distachya.
The var. chamelae, apparently confined to coastal Jalisco and Colima and adjoining Michoacán, has a fruit entirely compatible with var. distachya, but differs in relatively ample leaves, long pinnae, and large, incipiently revolute leaflets. In aspect it suggests M. guatemalensis, but the leaf- let-venation and broader, less prominently bullate craspedium agree with M. distachya sens, lat. It may deserve specific status.