Mimosa myriadenia (Benth.) Benth.
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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
Typus infra sub var. myriadenia indicatur.
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Description
Species Description - Prickly meso- and microphyllidious vines, potentially high-climbing in trees and forming impenetrable tangles in forest glades but sometimes precociously flowering as diffuse shrubs only 1-2m, armed along 5 low ribs of young stems and on ribs of most lf-stks and of some pinna-rachises with retrorse aculei to 0.3—1.3(—1.5) mm, the homotinous stems and all If- and inflorescence- axes pilosulous with short, forwardly incurved sordid hairs mixed with minute reddish scales, the foliage bicolored, the lfts dark-olivaceous (when dry brownish) and either glabrous or minutely thinly puberulent above, beneath paler and either glabrous, or puberulent along primary nerves, or thinly pilosulous overall, the inter-venium nearly always dotted with reddish (rarely pallid or fuscous) scales ±0.1 mm diam. (these rarely wanting, or confined to edge of blade), the inflorescence an effuse efoliate or proximally few-lvd panicle of loose amentiform spikelike racemes of small white fragrant fls exserted 1-4 dm from foliage. Stipules erect subulate 0.8-3.5 x 0.25-0.55 mm, nerveless or faintly 1-nerved, becoming dry and fragile in age. Leafstalks 6-28 cm, the petiole 1.3-4.5 cm, at middle 0.7-1.5 mm diam., the longer interpinnal segments 5-17 mm; a sessile, shallowly patelliform elliptic nectary 0.3-0.5 mm tall and 1.3-3.5 mm in long diameter near base of each lf-stk and smaller tubshaped or cupular ones below insertion of 1-3 (-5) distal pairs of pinnae, and on pinna-rachises below 1-8 distal pairs of lfts; pinnae of larger lvs 5-33-jug., a little decrescent proximally, the rachis of longer ones 2.5-7(-8) cm, the longer interfoliolar segments 0.6-8 mm; lfts of longer pinnae 8-40-jug., the small first pair 0.2-3 mm from subulate paraphyllidia 0.2-0.6 mm, the middle pairs (further described under each var.) linear-oblong or rhombic-oblong from subequilateral or strongly inequilateral base, either acute, rounded and mucronate, or obtuse, the longest ones 3-15 x 0.7-8 mm, the terminal pair dissimilar to the rest, obliquely oblanceolate or obovate, the blades all veinless or almost so above, beneath 1-5-nerved from pulvinule, the venulation becoming more complex with increasing width of blade. Racemes mostly fasciculate by 2-5 per node of inflorescence, each fascicle subtended by a rudimentary lf-stk bearing a patelliform nectary, each raceme without filaments 34 mm diam. and its pliant axis, including short 2-bracteolate peduncle, 3-7 cm, the narrowly obovoid fl-buds glabrous; bracts membranous lance-subulate 0.2-0.55 mm, becoming brown deciduous; pedicels 0.1-0.45 mm; flowers 5-merous 5-androus, all bisexual; calyx membranous campanulate 0.5-0.7 mm, externally either glabrous or puberulent, the deltate-triangular teeth 0.1-0.3 mm; corolla white (drying fuscous or blackish), turbinate 1.3-1.8 mm, the recurving lobes 0.7-0.9 x 0.5-0.7 mm, 1-nerved; filaments white, free to base, surpassing corolla-lobes by 1.2-2.5 (-3) mm; anthers ovate 0.45-0.55 mm; ovary short-stipitate. Pods 1-3 per raceme, pliantly pendulous, in profile linear-oblong, when well fertilized (5-)5.5-10 x 1—1.7(—1.9) cm, (8-)9- 12(-14)-seeded, at base abruptly contracted into a stipe (1-) 1.5-4.5 mm, the straight or nearly straight, either glabrous or puberulent, rarely randomly aculeolate replum 0.3-0.5 mm diam., the thinly papery olivaceous- or fuscous-brown valves low-bullate over each seed, dotted overall with minute red scales and usually otherwise glabrous but rarely pilosulous overall, when ripe breaking up (sometimes tardily and irregularly) into free-falling, individually dehiscent articles 4-8 mm long; seeds transverse at middle of pod, compressed-obovoid, in broad profile 3.7-4.6 x 2.5 -3.1 mm, the fawn or castaneous testa smooth sublustrous.
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Discussion
When Bentham first described M. myriadenia (in the genus Entada) and M. punctulata he possessed of each species only one collection and fruits of neither. It could not then be foreseen that the obvious differences between them in foliage would quickly be blurred by subsequent collections and eventually merge into a continuous range of variations in leaf-formula that is associated with a uniform inflorescence and pod. The variation in foliage between populations of M. myriadenia follows a familiar pattern of reciprocal adjustment between number of pinnae, size of leaflets, number of leaflets, and distance between successive pairs of leaflets along the pinna-rachis. In the long series of specimens now available for comparison, the typus of M. punctulata, with few pinnae and few broad, distant, dorsally venulose leaflets stands at one end, and those of taxonomically synonymous M. longi- caulis and M. myriadenia var. egena, with many pairs of pinnae and very numerous, narrow and crowded leaflets, at the other. On the upper-middle Amazon in eastern Loreto, Peru and in adjoining Brazil and Colombia plants of these extreme types are sympatric and appear to behave as distinct species. But outside the region of sympatry they are linked by indefinitely numerous intermediates collectively referred in herbaria to a heterogeneous M. myriadenia. Five segments of the full arc of variation correspond to the taxonomic varieties recognized herein, but there are no perceptible discontinuities between them.