Monographs Details: Macrolobium montanum var. potaroanum Cowan
Authority: Cowan, Richard S. 1953. A taxonomic revision of the genus Macrolobium (Leguminosae-Caesalpinioideae). Mem. New York Bot. Gard. 8 (1): 257-342.
Family:Caesalpiniaceae
Description:Latin Diagnosis - Arbor 10-13 m. alta, 1 dm. diametro, ramulis minute puberulis, glabrescentibus. Petiolus 8-11 mm. longus, glaber. Folia 2-3-jugata, paribus 10-17 mm. separatis; rachibus 15-32 mm. longis, glabris. Foliola 20-35 mm. longa, 10-20 mm. lata, oblonga, obovata vel oblongo-obovata, ad basim inaequalia, basis superiore latere cordato, inferiore acuto, ad apicem rotundata vel truncata, retusa, supra glabra vel sparsissime puberula in costa, infra glabra; costa saliens ambobus lateribus. Inflorescentiae 8 cm. longae, axe minutissirae puberulo, pedunculo 1.5 mm. longo; bracteis 1.5 mm. longis, 1 mm. latis, triangularibus, ciliolatis sed aliter glabris; pedicellus 4-5 mm. longus, glaber; bracteolae 8 mm. longae, 3.5 mm. latae, ellipticae, acuminatae, intus sparse pilosulae, extus glabrae. Hypanthium 2 mm. longum, stipite 0.5 mm. longo, glabrum. Sepala 3-3.5 mm. longa, 1-1.5 mm. lata, lanceolata vel elliptica, acuta ad acuminata. Petali lamina 4 mm. longa, 5 mm. lata, transverse ovale, unguicilus 5 mm. longus, auriculatus. Filamenta 21 mm. longa, glabra. Stigma simplex. Stylus 10.5 mm. longus, glaber. Ovarium 2 mm. longum, 1 mm. latum, lineare, glabrum, 2-ovulatum, gynophoro 3.5 mm. longo, glabro. Fructus immaturus 10 cm. longus, 2.5 cm. laws, oblongus, apicem versus latior, glaber, carpophoro 12-14 mm. longo, glabro, 1-3-seminifer.

Distribution and Ecology - Additional Specimens: BRITISH GUIANA: 85 miles Bartica-Potaro Road, Nor. 1947, Fanshawe 2758 (F.D. No. 5557) (BGF, U).

Discussion:

Type Collection: D. B. Fanshawe 764 (F.D. No. 3500), "83 miles Bartica-Potaro Road," British Guiana, July 1942 (HOLOTYPE BGF).

The diagnostic characters of this species clearly indicate its affinity with M. microcalyx and M. urupaense. It differs from the first of these by its less strongly dimorphic sepals, by its glabrous ovary, and its usually greater number of leaflets per leaf. From M. urupaense it may be separated by its fewer leaflet pairs, by its more or less pubescent bracteoles, and by its generally shorter, glabrous or basally villosulose filaments.

The two varieties included in this species are separable by the shape of their leaflets, length of their leaf rachises, size of their bracteoles, presence or absence of pubescence on the filaments, and by their geographic distribution.