Monographs Details: Macrosamanea
Authors:Rupert C. Barneby
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.
Scientific Name:Macrosamanea
Discussion:XIV. MACROSAMANEA Britton & Killip

Macrosamanea Britton & Rose ex Britton & Killip, Ann. New York Acad. Sci. 35: 131. 1936. — Sp. typica: M. discolor (Willdenow) Britton & Killip = Inga discolor Humboldt & Bonpland ex Willdenow = Inga adiantifolia Kunth, nom. illegit. — Mimosaceae trib. Ingeae gen. D., Nielsen in Polhill & Raven, Advances Legume Syst. 1: 190. 1981. — Etymology: Gr. macros, great + Samanea, from the aboriginal saman (rain-tree).

Pithecolobium sect. Samanea ser. Coriaceae [sic] Bentham, Trans. Linn. Soc. London 30: 589, sp. ult. exclusa. 1875 & in Martius, Fl. Bras. 15(2): 443. 1876 "Coriacea". — Sp. lectotypica: P. adiantifolium (Kunth) Bentham = Macrosamanea discolor (Willdenow) Britton & Killip.

Samanea sensu Pittier, 1927: 61, minori ex parte (spp. no. 6,7).

Pithecolobium ser. Coriaceae sensu Ducke, 1949: 39—41.

Unarmed, slender trees, arborescent shrubs either free-standing or sarmentose when crowded, or (in savanna and campirana) slender erect shrubs, either macro- or microphyllidious, the lfts mostly of firm texture, the capitula of relatively long and narrow, homomorphic, either sessile or pedicellate fls borne solitary or fasciculate by 2-5 in the axil of coeval or lately fallen lvs, or by suppression of the subtending lvs forming small, axillary or pseudoterminal (in M. kegelii cauliflorous), efoliate pseudoracemes of capitula, the branching essentially monopodial, but the terminal shoot often abruptly inhibited beyond the last node of the year’s growth; indumentum of short, gray or sordid hairs, sometimes scanty, or wanting below the fls. Stipules firm, deltate, triangular or linear-lanceolate, deciduous or exceptionally persistent. Lf-formula i—ix/2—26(—31); petiolar nectaries sessile, scutiform or patelliform or shallowly cupular, the first situated either next to lf-pulvinus, or between first pinna-pair, similar nectaries often between further pinna-pairs and near tip of pinna-rachises; lft- pulvinules usually broader than long, wrinkled; venation palmate and pinnate. Receptacle of capitula either subglobose, or pyriform, or stoutly linear-claviform, alveolate; bracts at base of capitulum either subtending the lowest 2-5 fls or immediately below them, commonly reflexed and charged ventrally with a nectary, but in M. amplissima the lowest bracts lacking nectary and deciduous but bracts of further fls bearing a nectary and persistent, and in M. kegelii and M. macrocalyx all bracts lacking nectary; perianth normally 5-merous but the teeth and lobes unequally cleft, sometimes confluent; calyx cylindric or cylindro-campanulate (4.5-)5-20(-26) mm, or in M. macrocalyx tumid and 20-29 mm; corolla narrowly trumpet-shaped, usually white and externally silky- pubescent, 11-63 mm; androecium 45-248-merous, the tube adnate at base to corolla, nearly as long as it or far exserted, the tassel either white or distally pink-tinged; ovary usually solitary, exceptionally 2 or 3 in M. froesii and M. consanguinea and so far as known 2-3 in M. macrocalyx, symmetrically linear-ellipsoid, tapering into style, surrounded at base by a variably developed but always perceptible disc; style shortly exserted from longer stamens, the stigma either porose or a little dilated; ovules 6-26. Pods sessile or almost so, in profile narrowly oblong or broad-linear, straight or gently decurved but never annular or coiled, either piano-compressed or becoming biconvex where elevated over obese seeds, the sutures not greatly thickened, the valves leathery; dehiscence inert, through the seminiferous suture and ultimately both sutures, the valves narrowly gaping to discharge the seeds; funicles subfiliform; seeds ellipsoid, usually strongly compressed and at least narrowly imbricate along the continuous seed-cavity, where overlapping and deformed by mutual pressure, the papery-membranous castaneous testa girdled by a prominent peripheral nerve, becoming fragile, wrinkled over faces of seed but pleurogram 0, loosely investing the homy fuscous embryo; endosperm 0. — A South American genus of 11species, the majority of riparian, seasonally flooded forest, two of seasonally wet sandy savanna or campirana, most diverse and numerous in the Amazon basin, extending N into the Orinoco valley and the Guianas, in an equatorial belt between 10°N and 10°S latitude.

The genus Macrosamanea has the homomorphic flowers, the compressed, inertly dehiscent pod, and the papery, exareolate seed-coat of Zygia, but differs in the long narrow perianth and with two exceptions (M. kegelii, M. macrocalyx) in characteristic nectaries on the inner face of bracts that subtend either the capitula or their individual flowers. The inflorescence of Zygia is with few exceptions (these unlike Macrosamanea in short calyx and slender corolla) cauliflorous, whereas the capitula of Macrosamanea are initially borne (except in M. kegelii) either directly pedunculate or in short pseudoracemes from coeval leaf- axils, the meristems of which may continue to function for some short time after abscission of the leaf. Leaves reduced to one pair of pinnae are stabilized in Zygia sect. Zygia whereas in Macrosamanea the pinnae are actually or potentially two or more pairs except in M. simabifolia. Nectaries on floral bracts that appear to be homologous with those of Macrosamanea occur in Archidendron ser. Stipulatae (Mohlenbrock) Nielsen (Opera Bot. 76: 9, fig 56(4). 1984), though in Archidendron when nectaries are present they are present on all bracts. This feature is unique to Macrosamanea among neotropical Ingeae, and by itself identifies to genus the great majority of specimens. The two species that lack this signature of Macrosamanea are nevertheless referred here because they share synapomorphies of the genus. The cauliflorous inflorescence and pale green coloration of the foliage of M. kegelii suggest a remote connection with Zygia sect. Marmaroxylon, where it would be anomalous in the form of the perianth. Macrosamanea macrocalyx is by any criterion an isolated species, notably distinct from the rest in the tumid calyx about two-thirds as long as the corolla, two or three ovaries per flower, and few ample, basally semicordate leaflets. This was described by Ducke as a member of Pithecolobium ser. Coriacea, and if not accommodated therein must be referred to a monotypic genus.

We exclude from Macrosamanea the anomalous Pithecellobium inundabile Ducke, first described by Ducke, on account of its simply pinnate leaves, as an Inga of sect. Leptinga, but later found to have dehiscent fruit similar to that of Macrosamanea and consequently referred to Pithecellobium. This species will be transferred to Zygia in Part II of this revision.

Macrosamanea was explicitly typified from the outset by M. discolor (Willdenow) Britton & Killip, which (under the invalid title of Pithecolobium adiantifolium) was a characteristic member of Pithecolobium ser. Coriacea Bentham. Kleinhoonte (1940: 329) extended the concept of Macrosamanea so far as to admit Balizia pedicellaris, a species of albizioid, not zygioid affinity, hence alien to the original core of Macrosamanea. It is in the sense of M. pedicellaris that Nielsen (1981: 182, fig. l/4a) subordinated Macrosamanea to Albizia, for he simultaneously recognized ser. Coriacea as a distinct but undescribed "genus D." We here adopt, with minor additions and adjustments, Nielsen’s evaluation of the genus, but adopt the already available name Macrosamanea.

Cassens and Miller (1981) stated that the wood of Macrosamanea is unique in the Ingeae in having both septate fibers and confluent parenchyma.