Pithecellobium x bahamense

  • Title

    Pithecellobium x bahamense

  • Authors

    Rupert C. Barneby

  • Scientific Name

    Pithecellobium x bahamense Northr.

  • Description

    4. Pithecellobium x bahamense Northrop, Mem. Torrey Bot. Club 12: 38, pl. 5. 1902, pro sp. sub Pithecolobio. — "... in fruit near Nassau [New Providence, Bahama Is.] in January, and in flower at Mastic Point, Andros, in June [1890], 605." — Lectotypus, J. I. & A. R. Northrop 605, the plant illustrated (with galled fruits), NY!; isotypus, NY!. — The paratypus from New Providence not seen.

    Pithecolobium mucronatum Britton in Shattuck, Veg. Bahama Is. 254. 1905. — "Dry thicket near Clarence Harbor, Long Island [Bahamas], W. C. Coker, July 16, 1903 (518)." — Holotypus, NY!. — Equated with preceding by Correll & Correll, 1982: 678.

    Pithecellobium bahamense sensu Britton & Rose, 1928: 22. P. mucronatum sensu Britton & Rose, 1928: 21.

    Shrubs ±1-3 m, in coppice diffusely branched but densely so, and of rounded outline in open places, either armed or not and either glabrous throughout or the young growth puberulent and the perianth finely silky, intermediate in foliage and size of nectaries between P. keyense and P. histrix. Stipular spines commonly 2-8 mm, or mostly reduced to appressed triangular blades 1 mm or less. Lf-formula either i/1 in all lvs, or i/1-2 in some lvs or in one pinna of some lvs, the lfts hence 4,6, or 8 per lf; petioles 1.5-10 mm, near apex 0.4-0.85 mm wide; lfts obovate or oblanceolate, either obtuse muticous (emarginate), or obtuse deltately apiculate, or abruptly mucronulate by excurrent midrib, the spinule at most 0.8 mm, the largest blades (10-) 12-35 x 4-16 mm; venation of small-lvd P. keyense. Inflorescence of P. keyense, the peduncles (1-) 1.5-5.5 cm, the receptacle 1.5-5.5 mm; fls extremely diverse in length and proportions, the perianth either glabrous or minutely silky-puberulent; calyx campanulate 1.5-3.1 x 0.8-1.3 mm, the triangular- subulate or deltate teeth 0.15-0.5 mm; corolla (3.5-) 3.8-8 mm, the lobes either erect or widely ascending; androecium 18-28-merous, 11-18 mm, the tube 1.6-6 mm, the free filaments pink or red, when relatively short much surpassed by the style; ovary glabrous (micropapillate), the oblong body 1.6-1.9 mm, the stipe as long or slightly longer, 1.8-3.1 mm. Pods of P. keyense, sometimes fewer-seeded.

    In coppice, at savanna margins, and in barren ground along and near the beach, below 50 m, sym- patric with one or both parents in the central Bahamas (Andros, New Providence, Exuma, and Long Island) and along the keys of N Cuba (Matanzas, Camaguey, E to border of NW Oriente). — Map 3. — Fl. sporadically throughout the year. — Ram’s horn.

    We have no experimental evidence that P. x bahamense consists of hybrids derived from P. keyense and P. histrix, although the evidence from morphology and dispersal is persuasive. The supposed hybrids resemble P. keyense in random quadrifoliolate pinnae and in the nectary (almost always) at tip of each pinna, but differ in the mucronulate leaflet-tips (Fig. 1, no. 6). Pithecellobium x bahamense resembles P. histrix, the other putative parent, in diminished foliage, which is, however, variable. The characters by which the parent species differ from one another appear in a series of intermediate states in the hybrids. The flowers of P. histrix are relatively few per capitulum and relatively long, with filaments united into a tube 6-9.5 mm long, whereas those of P. keyense are relatively short, with tube not over 3.5 mm long. In P. x bahamense the corolla is extremely variable in length, and the gynoecial tube varies from 1.6 to 6 mm. With one exception, the hybrid occurs on islands or keys from which both parents have also been collected, the exception being Long Island, from which P. keyense, but not P. histrix, is definitely known. Moreover, the hybrid has no known independent range. It is implausible that three related species, so similar in leaf-formula, flower structure, and fruits, could coexist in one place, such as Mastic Point on Andros, and maintain their genetic identity.

    The quantitative characters that lend credence to the idea of a hybrid origin of P. x bahamense are but poorly reflected in the topology of the cladogram (Fig. 1). Pithecellobium x bahamense is not sister- species to either of the putative parents, but it is not far removed either. It is a member of the clade including P. histrix, with which it shares mucronulate leaflet-tip (no. 6) and loss of nectary on the pinna- rachis (no. 3, a reversal), but differs from P. histrix and its sister-species P. cynodonticum in having intemodes longer than the stipules. Pithecellobium x bahamense is further removed from P. keyense, which lacks the mucronulate leaflet-tip (no. 6). Both of the latter do have axillary pseudoracemes (no. 10), though this character is not synapomorphic.