Monographs Details: Macrolobium campestre var. longibracteatum R.S.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 parva, ramulis foliisque glabris. Petiolus 20-28 mm. longus, leviter canaliculatus. Folia 2-3-jugata, paripinnata; rachibus 3-5 cm. longis, leviter canaliculatis. Foliola 6-11.5 cm. longa, 2.5-4.5 cm. lata, ovata, ovato-lanceolata vel lanceolata, ad basim obtusa ad acuta, ad apicem acuminata. Inflorescentiae 16-18.5 cm. longae, axe brevi-pilosulo; bracteis 10-12.5 mm. longis, lanceolatis, acuminatis, brevi-pilosulis; bracteolis 8.5 mm. longis, 3 mm. latis, ellipticis, acuminatis, extus pilosulis, intus glabris vel sparsissime brevi-pilosulis. Sepala 2-3.5 mm. longa, 1-2 mm. lata, lanceolata. Petali lamina 4 mm. longa, 6 mm. lata, unguicilo 5 mm. longo. Ovarium 2-3 mm. longum, 1 mm. latum, glabrum, 3-ovulatum, gynophoro 1.5 mm. longo, puberulo. Fructus ignotus.

Discussion:

Type Collection: A. Ducke 1242, "Entroncamento, Belem," Para, Brazil, June 1943 (HOLOTYPE MO, isotypes IAN, NY, US).

Unquestionably, the relationship of this species is with M. arenarium, but this pair of species is completely without ties to the other species of the genus. They may be regarded as the two extremes of a distinct line of relationship from which one group of unijugate species may have diverged. Macrolobium campestre exhibits the following characters which amply distinguish it from its only certain relative: (1) it has 2-3-jugate leaf blades, and (2) its bracts and bracteoles are pubescent, on one side at least.

Five subspecific taxa are recognized within this species and are here treated as varieties. Though these are "definitely accepted by the author," there is the realization that future collecting within the range of the species may very well merge some of the less distinct of these. However, in view of the data available, this disposition of the variants appears to be at least a practical solution to the problem.

Plants of the typical variety may be recognized by their shrubby habit, their relatively broad leaflets and by their pilose bracts. Only var. arirambense approaches it in aspect and the latter (var. arirambense) has very elongate inflorescences, the axis of which is short-pilosulose and its branchlets are puberulous. The relationship of the last-mentioned variety is much nearer var. longibracteatum, from which it is distinguished by its puberulous branchlets, differently shaped and smaller leaflets, longer inflorescences, and smaller bracts. The inflorescences of var. longibracteatum and arirambense are considerably longer than in any of the other varieties and are distinctly arcuate, suggesting that they may be pendent in nature.

Var. arboreum is quite distinct by virtue of its narrow leaflets which are smaller on the average than those of plants of the other varieties. It becomes a tree of considerable proportions, attaining heights of 35 m. according to the field notes of B. A. Krukoff. These characteristics and its longer, differently shaped bracts serve to separate it from its nearest relative, var. medium. As the epithet of the latter implies, this variety is transitional, between var. longibracteatum and arboreum. Its shorter bracts, puberulous bracteoles and shorter inflorescences serve to distinguish it from var. longibracteatum.