Abarema barbouriana (Standl.) Barneby & J.W.Grimes
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Authors
Rupert C. Barneby
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Authority
Barneby, Rupert C. & Grimes, James W. 1996. Silk tree, guanacaste, monkey's earring: a generic system for the synandrous Mimosaceae of the Americas. Part I. Abarema, Albizia, and allies. Mem. New York Bot. Gard. 74: 1-292.
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Family
Mimosaceae
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Scientific Name
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Type
"Panama: Zetek Trail, Barro Colorado Island, Canal Zone, October 27. 1931, Otis Shattuck 237" — Holotypus, F!; isotypus, MO!
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Description
Species Description - Trees attaining 30 m in lowland habitats but often smaller, flowering as bushy treelets at 3 m or in upland habitats remaining bushy at maturity, the trunks attaining 2-3 dm dbh, the young branches and all axes of lvs and inflorescence densely sordid- pilosulous with erect or forwardly incurved, yellowish or reddish brown hairs to 0.2-0.8(-l) mm, the foliage bicolored, the mature lfts firm, on upper face lustrous dark green glabrous (except for sometimes ciliolate midrib), either smooth, or wrinkled, or finely venulose, the concave lower face pallid, pilosulous or softly silky-villosulous with ascending or erect hairs or (locally) glabrous except for strigulose-pilosulous, always cariniform midrib, the capitula of greenish white, white-stamened fls solitary or paired in the axil of coeval lvs, immersed in foliage. Stipules subulate, linear-elliptic, or linear 1-3(-4) mm, caducous. Lf- formula (ii—)iii—xii/(7—)8—22; lf-stks of larger lvs 2-14.5 cm, the petiole including pulvinus (6—)7—15 (-17) mm, the longer interpinnal segments 7—16(—18) mm; petiolar nectaries plane or shallowly cupulate, round or elliptic, either sessile against lf-stk or stipitate and in profile to 1(—1.6) mm tall, the first one near or well above mid-petiole, sometimes close to first pair of pinnae, (0.4-)0.6-1.7(-2) mm diam, progressively smaller but otherwise similar nectaries below some distal pinna-pairs, and yet smaller, more slenderly stipitate ones below 2—7 pairs of lfts; pinnae strongly decrescent proximally, sometimes a little so distally, the rachis of those near and above mid-lf 3-7 cm, the longer interfoliolar segments 2.5-10 mm; paraphyllidia to ±0.5 mm nearly always present; pulvinules 0.2—0.65 x 0.4—0.75 mm; lfts decrescent proximally but thence subequilong except for broader and sometimes longer furthest pair, the blades obtu-sangulately rhombic, rhombic-oblong or -elliptic around a diagonal, almost straight or distally incurved midrib, inequilaterally flabellate-cuneate at base, either obtuse or obtuse-apiculate, the largest (4.5-) 5 21 x (2-)2.6-10 mm, 1.9-2.7 times as long as wide; the subcentric midrib giving rise on each side to (2—)3—9 major (but never strong) secondary nerves weakly anastomosing close within the revolute or almost plane margin, these often raised only on hypophyllum but sometimes also, with tertiary venulation, on upper face. Peduncles 1.5-8 cm; capitula ±12-20- fld, the clavate receptacle including short terminal pedestal 2-4 mm; bracts ovate-triangular, elliptic or narrowly oblanceolate, 0.75-2.0 x 0.5-0.75 mm, deciduous; fls dimorphic, all sessile or the lowest peripheral ones borne on obscure pedicel not over 0.5(-0.7) mm long (or in Ecuador to 2.5 mm; see discussion of var. barbouriana, below), the perianth of all 5-merous (random irregularities), densely silky- appressed-pilosulous externally overall; PERIPHERAL FLS: calyx deeply campanulate or turbinate-campanulate (2.5-)3-6 x 1.7-2.4 mm, the triangular, often unequal teeth 0.6-1.3 mm; corolla (4.5-)5-8 mm, the lobes (1-) 1.3-3 mm; androecium (12—) 14— 28(randomly 36, 48)-merous, 21-30(-35) mm, the stemonozone 0.6-1.5 mm, the tube 1.4-6.5 mm; ovary substipitate, conical at apex, densely pubescent; TERMINAL FL: calyx 3.5-6 x 1.6-2.4 mm; corolla 7-12 mm; filament tube 6-16 mm. Pods usually solitary, sessile, in profile undulately broad-linear and (when well fertilized) evenly incurved through 1-2.5 circles 3.7-4.4 cm diam, (5—)6—12 x (1-) 1.1-1.6 cm, 6-12(-14)-seeded, the stiffly papery, brown or fuscous, finely venulose valves framed by sutures 1.4—2 mm wide, low-convex over each seed, either strigulose or pilosulous overall (but especially along sutures) with sordid or yellowish hairs to 0.3-1.2 mm, the endocarp orange-red either overall or only in the seed-cavities; dehiscence downward through both sutures, the valves coiling; seeds (few seen) plump, ±5-7 mm diam, the translucent testa revealing the bluish embryo, the pleurogram either 0 or complete, ±1.5 mm diam, faintly engraved.
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Discussion
Our concept of Abarema barbouriana, which has been reported hitherto only from Panama and northern Colombia, is expanded herein to include Pithecellobium arenarium of Venezuelan Guayana and northern Amazonian Brazil, P. fanshawei of Guyana and French Guiana, and related forms, never satisfactorily identified, from mountainous northern Venezuela. It now accommodates a range of leaf-formulas comparable to and only slightly higher than those long admitted to the closely related A. jupunba, and considerable variation in pubescence of leaflets and pod, in venulation of leaflets, and in size of floral parts. Particular characters appear to be linked to dispersal and are dominant locally but feebly correlated; they suggest incipient racial differentiation, but are incalcitrant to precise definition. As in A. jupunba, we recognize only two subdivisions of the species: a relatively microphyllidious var. barbouriana, most abundant west of the eastern cordillera in Colombia and in east-central Panama, and thence interruptedly scattered eastward to the Guianas; and a relatively macrophyllidious var. arenaria, most frequent on the Gran Sabana and on tepuis of Venezuelan Guayana but recurring in lowland white sand savanna habitats on the sources of Río Negro in Venezuela and in central Amazonian Brazil. Each of these varieties encompasses variant populations that are analyzed below but is not further dismembered taxonomically. It should be emphasized that the fruit, except for the length and orientation of its indumentum, remains extremely constant.
As here redefined, A. barbouriana differs from A. jupunba primarily in the larger flower, and not quite consistently in the loose silky pubescence of the hypophyllum. Where this indumentum is lacking or sparse, the flower is much larger than that of A. jupunba or the leaflets are smaller and more numerous. The fruits are essentially alike.