Monographs Details: Macrolobium acaciaefolium (Benth.) Benth. & Mart.
Authority: Maguire, Bassett, et al. 1953. The Botany of the Guayana Highland. Mem. New York Bot. Gard. 8 (2): 87-160.
Family:Caesalpiniaceae
Description:Species Description - Tree with rather flattened, expanded crown, 3-30 m. tall, 8-100 cm. diameter, the branchlets glabrous to densely pilosulose. Petioles (2-)6-7(-12) mm. long, canaliculate. Leaf blades oblong, elliptic-oblong or lanceolate-oblong, (12-)15-20 (-28)-jugate, the pairs of leaflets (3-)5-7(-12) mm. apart; rachis (6.5-)10-14(-24) cm. long, glabrous or the axis puberulous or pilosulose on the upper surface and pilosulose beneath, the wings only cioliolate or the upper surface also puberulous or pilosulose, glabrous beneath. Leaflets (7-)20-25(-40) mm. long, (2-)5-7(-11) mm. wide, the uppermost leaflets smallest, oblong, the base inequilateral, the upper side subobtuse to cordate, the lower side acute to obtuse, the apex rotund, retuse to emarginate, usually minutely apiculate; upper surface usually shiny, glabrous, or puberulous to pilosulose on the costa or sometimes more or less puberulous on the blade also, the lower surface glabrous to more or less strongly golden-pilose on the apical-lateral surface of the costa, extremely rarely pilosulose on part or all of the blade; costa impressed on the upper surface, salient beneath, the venules obscure to prominulous. Inflorescences (1-)2(-6) cm. long, densely grayish-pilosulose, infrequently with one basal branchlet, the peduncles (when present) about 4 mm. long; bracts caducous, (1.5-)3.5(-6) mm. long, (1-)2.5(-5) mm. wide, broadly ovate to oval, or oblong, concave, acute to cuspidateacute, ciliolate, glabrous or rarely minutely strigulose near the base within, densely pilosulose externally; pedicels (1.5-)2.5(-5) mm. long, densely pilosulose; bracteoles (3-5-)5(-7) mm. long, (1.5-)3(-4) mm. wide, concave, obovate to oval to ovate, glabrous within, densely pilosulose externally. Hypanthium 1-2 mm. long, sessile or with a stipe 0.5 mm. long, glabrous or sparsely pilosulose basally. Sepals five, the adaxial pair partly united, 2.5-6.5 mm. long, 1-3.5 mm. wide, oblong to lanceolate, obtuse, acute, or acuminate, glabrous or rarely ciliolate sparsely at the apex. Petal blade 3-5.5 mm. long, 5-7.5 mm. wide, transversely oval, rarely suborbicular, the claw 3-5-5 mm. long, more or less auriculate, glabrous externally, villosulose within on the claw and over the center of the blade or the blade totally glabrous, the claw ciliolate in the lower part; 1-4 petalodia often present, to 5 mm. long, linear. Filaments (12-)15(-20) mm. long, glabrous. Stigma capitellate. Style (9-)15(-20) mm. long, basally pilosulose. Ovary 2-3 mm. long, 1-1.5 mm. wide, oblong to oval or oblong-obovate, (l-)2(-3)-ovulate, the margins pilosulose, the lateral surfaces glabrous; gynophore 1-2.5 mm. long, pilosulose, the hairs usually directed basally, inserted at the base of the hypanthium or sometimes up to midway on its adaxial wall. Fruit indehiscent, 4.5-7 cm. long, 3-5.5 cm. wide, oblong to orbicular, flat, the adaxial margin thicker than the abaxial and sulcate, sparsely pilosulose on the margins, the carpophores 1-2.5(-6) mm. long, pilosulose. Seeds one per fruit, 3-4.5 cm. long, 2-3-5 cm. wide, flat, oval or oblong, the testa crustose, tan-brown to black, irregularly salient-venose.

Discussion:

Outea acaciaefolia Benth. Jour. Bot. Hook. 2: 94. 1840.

Vouapa acaciaefolia (Benth.) Baill. Hist. PI. 2: 109. 1870.

Vuapa acaciaefolia (Benth.) Kuntze, Rev. Gen. 1: 213. 1891.

Macrolobium acaciaefolium (Benth.) Benth. var. vestitum Sandwith, Kew Bull. 1948: 312. 1948.

Type Collection: Robt. Schomburgk 521, "Rooponoony and Essequibo Rivers," 1838 (HOLOTYPE K, isotypes BM, F, G, K, P, US, W).

Vernacular Names: Brazil: "arapary," "faveira arapury," "parapari"; Peru: "pas h aqu i l l a»" "arapari"; Venezuela: "arepillo," "arepito."

This is an extremely variable species within which there may even be some subspecific taxa, but no constant characters have been discovered in this study which could be used to distinguish them.

In vesture there is marked variability. The leaflets are typically pubescent on the costa on the upper surface and on the apical-lateral surface of the costa beneath. However, collections from eastern Peru and Colombia have the upper half of the blades more or less pubescent beneath. This pubescence distribution might be of some taxonomic use, were it more constant and correlated with other more significant differences. Unfortunately, such is not the case, for this character appears to vary independently of all others. Collections which exhibit this pubescence distribution are: Tessmann 3673, Schultes & Black 8640, Cuatrecasas 4008 and Allen 3394. In the upper Rio Negro country a form occurs which is completely pilose on the undersurface of the leaflets, represented by Williams 14485 and Maguire, Cowan, & Wurdack 29504. However, this is the only distinguishing character and is considered to be only one extreme in the pubescence variation pattern.

There is another variant group with no geographic or morphologic character other than that it has generally larger leaflets. As with the pubescence, it is held that no useful purpose is served by the recognition of subspecific taxa in what appears to be a continuous system of variability.

Var. vestitum, here treated as a synonym of this species, was described by Sandwith to include that portion of the species which exhibits pubescent branchlets but even the type collection shows scattered hairs on the branchlets of some of the sheets observed. Actually, the branchlets may be glabrous, pilosulose in a small area just above each node, sparsely but generally pilosulose, or densely pilosulose.

This species is so similar to M. longeracemosum in aspect that some of the material of that species had been determined as M. acaciae folium and there is no doubt that the two are intimately related. They are, however, separable on a number of characters both in the vegetative phase and in the reproductive structures. Whereas M. longer acemosum has the leaflet costa strongly salient on the upper surface, in the present species it is impressed. Also, the leaflets of M. acaciaefolium do not display the sharply contrasting dark-lustrous upper surface and strongly glaucous undersurface as do those of M. longer acemosum. The pubescence of the bracteoles and pedicels of the latter is quite different from that on the same structures in M. acaciae folium. The fruits of the latter are oval, oblongoval, or orbicular, and indehiscent, in contrast to the elongate-oblong fruits produced by its nearest relative.