Mimosa lanuginosa Glaz. ex Burkart
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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
402. Mimosa lanuginosa Glaziou ex Burkart, Darwiniana 13(2-4): 379. 1964.—Typus infra sub var. lanuginosa indicatur.
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Description
Species Description - Virgately erect subshrubs from xylopodium, (6—)8—16 dm, the simple or distally branched stems arising each year or sometimes enduring (if not burnt) into a second season, when young densely clothed from base to inflorescence with short sessile spreading-recurved lvs (in var. some proximal lvs distinctly petiolate), proximally defoliate in age, the young stems, lf-stks and axes of inflorescence densely silky-pilose-tomentose with fine, arborescently branched setae, those of stem and pedicels always flagelliform, silky and to (l-)2-4.5 mm, those of white-silky or -velvety lfts sometimes shorter, the vesture often tarnished in age, the inflorescence a well exserted, simple pseudoraceme or narrow panicle of globose capitula. Stipules linear-attenuate or setiform, 4-9 x 0.3-0.6 mm, densely setose externally, early dry caducous, absent from many specimens. Leaf-stalks all reduced to the pulvinus or (var. raduliformis) in some lvs to 2.5-5 cm; pinnae 1-jug., the axis of each commonly less than 3, rarely to 8 cm, the interfoliolar segments 2-8 mm; lfts mostly 3-5-, rarely to 7-11- jug., subaccrescent distally, the first pair close to pulvinus and its anterior member diminutive, all in outline obliquely lanceolate to oblong or subdimidiately ovate-elliptic, obtuse apiculate, the larger ones of lvs near mid-stem (11—) 13— 28(—33) x (3—)5—13(—18) mm, their anterior margin slightly convex, their posterior one broadly rounded, the blade (2-)3-5-nerved from pulvinule, the straight midrib dividing it 1:2.5-3, the other nerves all posterior, incurved-ascending and expiring within the scarcely dilated margin, all nerves immersed or almost so above, beneath bluntly prominulous. Peduncles solitary (0.5—) 1—4 cm; capitula without filaments 9-13 mm diam., prior to anthesis conelike and densely silky-pilose; bracts linear-oblanceolate or -attenuate 3-5 x 0.4-0.6 mm, dorsally at and above middle pilose with fine setae to 1-3 mm; flowers 4-merous 4-androus, many lower ones commonly staminate; calyx paleaceous stramineous, 4-angulate 2.5-4.8 mm, glabrous except at very base, the lacerate-setiform lobes 1-1.8 mm; corolla (3.8-)4-6 mm, narrowly tubular-funnelform, the firm ovate cymbiform lobes 0.8-1.4 x 0.6 mm, externally either glabrous or thinly puberulent at tip; filaments pink, monadelphous through 2-2.5 mm, exserted 6-7.5 mm. Pods few per capitulum, sessile and usually embedded in sterile fls, potentially 3- but mostly only 1-2-seeded, in profile oblong or oblong-elliptic 7-14 x 4-5 mm, the replum 0.2-0.35 mm wide, the papery low-convex valves densely silky-pilose overall with loosely ascending subfiliform cream-colored silky setae to ± 3 mm, when ripe separating from replum and breaking up into indehiscent articles; seeds not seen well-preserved.
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Discussion
Mimosa lanuginosa is visually and tactually notable for the soft silky or plushlike, pallid indumentum that clothes the stems and leaves, a vesture unique in ser. Polycephalae. It is closely related, nevertheless, to vicariant M. radula and its sympatric vars. imbricata and radulina, with which it shares a wandlike, densely foliate stem and the paleaceous calyx of the series. When Burkart described M. lanuginosa as a member of ser. Lepidotae (sec. Calothamnos of this revision) he admitted that its genetic affinity lay in the direction of ser. "Meticulosae" from which it was technically excluded by the character of arborescent hairs and by lack of a strong marginal nerve on the leaflets. This nerve, however, is in effect present, though not very pronounced and concealed by dense pubescence. Burkart noted that some hairs of M. (Meticulosae) radula bear toward the base small emergent cells that prefigure the arborescent ramification seen in M. lanuginosa, and the difference is more in degree than in kind. Similar scaberulous hairs are now known to occur in several related taxa of ser. Polycephalae, and seem clearly homologous with branched hairs of M. lanuginosa. It is high time to abandon a typological concept which subverts classification according to genetic affinity. This has become more urgent and inevitable with the discovery of M. lanuginosa var. raduliformis, in which the arborescent trichomes of M. lanuginosa are associated with the leaf-formula and spiciform inflorescence of M. radula, and of a second species of this series, M. thermarum, also pubescent with branched hairs.
Typical M. lanuginosa resembles M. radula var. imbricata in having all leaves sessile against the stem, but it has only 4-5 (not 7-16) pairs of leaflets in longer pinnae. The poorly documented var. raduliformis resembles in leaf-formula and some distinctly petiolate lower leaves the relatively scarce M. radula var. radula.