Mimosa radula Benth.

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 radula Benth.

Type

403. Mimosa radula Bentham, J. Bot. (Hooker) 4: 377. 1841, sensu hie ampliato.—Typus infra sub var. radula indicatur.

Description

Species Description - Stout, in most seasons functionally herbaceous subshrubs with 1-3, rarely several stems erect or stiffly assurgent from xylopodium, either simply virgate or beyond middle paniculately few-branched, attaining (7-)10-16(-20) dm, clothed from base to leafless or proximally leafy-bracteate, far-exserted pseudoracemose inflorescence either with crowded and recurved or more distant and ascending or outwardly curved lvs, the axes of stem and inflorescence and the dorsal rib of pinnae at once densely puberulent and either hispid or silky-pilose with spreading, retrorse, or partly ascending, smooth or scabemlous setae to 0.6-3.5(-4) mm, the subconcolorous lfts dull brownish-olivaceous except when concealed by vesture, pilosulous on both faces (except var. semitonsa), palmately veined beneath. Stipules firm erect, linear or narrowly lanceolate 4-11 x 0.4—2 mm, setose dorsally, glabrous within, early dry deciduous. Leaves either all sessile against stem or some lower and median ones petiolate, the petioles when present progressively shorter upward along stem; pinnae 1-jug., 2-21 cm, the longer interfoliolar segments 2-22 mm, the lfts sometimes more crowded in upper than in lower lvs; lfts 4-18(-22)-jug., decrescent proximally but scarcely so distally, the first pair contiguous to pulvinus and the anterior member of the first or of the first two pairs smaller than its fellow, sometimes reduced to a paraphyllidium, the blades otherwise lanceolate to semi-ovate or sub-dimidiately cordate, obtuse or acute, the larger ones of a plant (10-) 12-55 x 3-30 mm, all at base rounded on proximal and cuneate on distal side, (2-)3-6-nerved from pulvinule, the displaced midrib dividing blade 1:2.5-6, the nerve on its anterior side either submarginal or obsolescent, those on posterior side incurved-ascending, in broader lfts weakly brochidodrome within the continuous setose margin, the venation pallid and raised on lower face only, there sometimes obscured by vesture. Axis of inflorescence 1.5-6 dm, exserted from developed lvs 1.5-3.5(-4) dm, the solitary peduncles (0.5-)l-4 cm; capitula without filaments (7-)8-12(-14) mm diam., prior to anthesis usually conelike and pallid-setose, but bracts sometimes hardly as long as the lustrous 4-angulate, glabrous or microscopically puberulent fl-buds, the capitula then submoriform; bracts linear-oblanceolate or -spatulate (2.5-)3- 5 x 0.2-0.5 mm, beyond middle densely setose dorsally and setose-ciliate; flowers 4-merous 4-androus, some lower ones commonly staminate and smaller than the rest; calyx paleaceous, glabrous except sometimes for a ring of setae at very base, obtusely tetragonal (1.8-)2.5-4.2(-4.8) mm, the four deeply lacerate or setiform-decompound lobes 0.7-1.8 mm; corolla 3-5.2(-6) mm, narrowly vase-shaped or when long subtubular, the narrowly ovate cymbiform subcomeous, dorsally lustrous lobes 0.7-1.3 x ±0.4 mm; filaments pink or purplish, monadelphous through 1.5-2.5 mm, exserted 5.5-8.5 mm. Pods (not well known) usually many per capitulum but not forming a hard ball, sessile, in profile narrowly oblong, cuneate at both ends, ±12-16 x 4.5-5 mm, 2-3-seeded, the replum 0.4-0.5 mm wide, the papery valves ±0.15 mm thick at margins but thinner and low-convex over each seed, densely hispid-pilose overall with fine tapering or at base strongly dilated, forwardly curved setae to 1-3 mm, the ripe valves separating from replum and breaking up into free-falling, individually indehiscent articles 4-5 mm long; ripe seeds not seen.

Discussion

Mimosa radula may be recognized by this syndrome of characters: multifoliate virgate stems, mostly one meter tall or more, passing upward into an efoliate pseudoraceme or few-branched panicle; cauline indumentum composed of setae either perfectly smooth or scaberulous, but not arborescently plumose; leaflets relatively few (420 pairs) per pinna and relatively ample (some over 1 cm long); and the paleaceous calyx and monadelphous filaments of its series. Native to small portions of its extensive planaltine range of dispersal are M. virgula, almost a microphyllidious version of it, which has leaflets of much the same number but much less than one centimeter long; and the habitally similar M. thermarum and M. lanuginosa, which differ in arborescently plumose cauline setae. The virgate growth-habit and leaf-formula of M. radula are deceptively repeated, at the eastern margins of the Brazilian Planalto, by members of ser. Brevipedes, but these have very small or obsolete, non-paleaceous calyx and free filaments.

In 1875-1876 Bentham had seen ten miscellaneous examples of the species here described as M. radula sensu lato, and interpreted them as representing three distinct but related species, one of them with a variety, of which the critical features were length of petioles, number and size of leaflets, and length of peduncles. With the advantage of eight times as many collections, and consequently a much more accurate notion of the dispersal of individual variations and the constancy of correlations between them, the modem student cannot accept M. radula, M. calycina, M. imbricata and its var. multijuga, and M. dimidiata at the rank to which Bentham assigned them. The characters emphasized by Bentham have turned out to be independently variable, leaflet-size and -number are less exact than could be predicted a century ago, and some supposed discontinuities have been filled in by intermediate states then not known. In place of Bentham’s five taxa I find it possible to recognize herein five varieties of one species M. radula, three of them incorporating all Bentham’s material, and two newly described.