Mimosa orinocoensis

  • Title

    Mimosa orinocoensis

  • Authors

    Rupert C. Barneby

  • Scientific Name

    Mimosa orinocoensis Barneby

  • Description

    268. Mimosa orinocoensis Barneby, sp. nov., M. pellitae adspectu similis et proxime affinis, sed ab ea setis caulinis de latere supra basin retro-calcaratum affixis, stipulis saltern ultra mediam dorso glabris crasse 6-8-nerviis, et calyce minimo haud vel vix paleaceo-lobulato distans, leguminis articulis septo 0.6-1 mm lato utrinque clausis cum M. pellita var. pellita congruens sed valvulis applanatis nec turgidis articulisque ipsis longioribus, ad medium legumen 4.5-8 (nec 2.5-4.5) mm longis diversa.—Venezuela. Barinas: este de El Cantón, a lo largo del río Cáparo, 100 m, 12.IV. 1968 (fl, fr), J. A. Steyermark (with G. Bunting & C. Blanco) 102233. —Holotypus, NY (2 sheets).

    Scandent shrubs attaining 3 m or more, armed on stems and lf-stks with sharp recurved brownish pallid-based cat’s-claw aculei 2-4 mm, the slender livid-brown homotinous branches at once minutely pubemlent and strigose with forwardly subappressed, basally spurred brownish tapering setae to 0.8-2.5 mm, the foliage moderately bicolored, the lfts brown-olivaceous sublustrous glabrous above, paler and minutely silky-strigulose beneath, often proximally ciliolate, the globose or plumply ellipsoid capitula solitary and 2-3(—4) together in the axil of coetaneous or quickly hysteranthous lvs, at first a shortly exserted pseudoraceme but early immersed in lvs. Stipules erect, ovate or broadly lanceolate 2-4 x 1.3-2 mm, dorsally either glabrous throughout or pubemlent below middle, coarsely 6-8-nerved, persistent. Leaf-stalks (6—)8—15 cm, the petiole including pulvinus 3-11 mm, the longer interpinnal segments 8-16 mm, the narrow ventral groove bridged between each pinna-pair and charged with an ascending burnished yellowish spicule 1.5-5.5 mm; pinnae 9-15(-16)-jug., of irregular lengths but usually decrescent proximally, the rachis of longer ones 3-5.5 cm, the longer interfoliolar segments 0.8-1.4 mm; lfts of longer pinnae (25-)30-48-jug., subdecrescent at each end of rachis, the first, often unequal pair 0.4-0.7 mm distant from subulate paraphyllidia 0.2-0.5 mm, the blades linear from obtusangulate or shortly auriculate base, acutely apiculate, those near mid-rachis (4-)4.5-9 x 0.8-1.6 mm, (4.5-)5-7 times as long as wide, all veinless above, beneath finely (4-)5-nerved from pulvinule, the outer posterior nerves very short, the slightly displaced, simple or faintly few-branched midrib, the inner posterior nerve and the submarginal anterior one all produced to blade apex. Peduncles 12-16 cm; capitula without filaments 6-7 mm diam., prior to anthesis moriform, the 4-ribbed fl-buds scabrous-setulose at apex, the receptacle becoming 3-5 mm; bracts submembranous linear-oblanceolate 0.7-1.2 mm, weakly 1-nerved, dorsally glabrous, ciliolate; flowers 4-merous 8-androus, some lower ones staminate; calyx shallowly campanulate or saucer-shaped 0.3-0.6 mm, glabrous externally, the rim undulate or obscurely pallid-ciliolate but not paleaceous-lobulate; corolla narrowly vase-shaped 2.3-2.8 mm, the ovate 1-nerved lobes ±0.8 x 0.6 mm; filaments whitish or pinkish, united at base into a stemonozone less than 0.5 mm, the 4 longer ones exserted 3-3.5 mm. Pods 2-7 per capitulum, in profile broad-linear planocompressed 7—10 x 1.3—1.6 cm, 12—18-seeded, contracted at base into a stipe 2-6 mm, broadly rounded and sometimes cuspidulate at apex, the replum 0.4-0.7 mm wide, indented only where ovules abort, densely hispid on back and sides with coarse yellowish setae ± 1.5-2.5 mm, often in addition minutely whitish-puberulent, the papery sublustrous livid valves likewise hispid with erect, somewhat longer coarse setae arising from a pallid pediment, either glabrous between the setae or minutely puberulent over seeds, when ripe breaking into transversely oblong, free-falling indehiscent articles 4.5-8 mm long, each sealed at both ends by a septum 0.6-1 mm wide; seeds transverse, compressed-ellipsoid 6.5—7 x 3-3.3 mm, the testa dull olivaceous.

    On forested river-banks below 150 m, scattered through the middle and lower Orinoco basin in n.-e. Colombia (Vichada) and Venezuela (centr. Barinas and n.-w. comer of Terr. Fed. Amazonas downstream to the Delta); on lower Amazon river in Pará, Brazil; and once collected in the Magdalena valley near 6°N in inter-Andean Colombia.—Flowering and fruiting nearly through the year. Map 37.

    Mimosa orinocoensis was collected first in 1886 on the lower Orinoco by Rusby & Squires (17, 197, NY). Their number 17, consisting of a flowering stem and a detached pod, was sent by Britton to Kew for comparison with allied forms named by Bentham. N. E. Brown, who made the comparisons, believed the pod to be extraneous and pronounced the flowering element an exact match for plants from southeastern Brazil referred by Bentham to M. cinerea Veil. Brown was mistaken on both points, and Britton, evidently dissatisfied, annotated the sheet with an unpublished name. Subsequent collections from the Orinoco valley show the same broad and strongly flattened pod, characteristically hispid with stout setae arising vertically from a pallid pediment, attached to the foliage of Rusby’s plants. In stipules and foliage these indeed do resemble some examples of Brazilian M. elliptica, but the spurred cauline setae, the abbreviated calyx, the number of seeds per pod, and the ecology and dispersal are all different. As it emerges belatedly from the shadow of composite M. pigra auct., M. orinocoensis is seen to possess the distinctive syndrome of glabrate venose stipules, cat’s-claw prickles on stem and leaf-stalks, spurred setae, diminished calyx and broad pod breaking up into water-borne articles, these coinciding with a natural area of dispersal.