A New Species of Gagnebina (Leguminosae: Mimosoideae) from Madagascar

Abstract

A new species of Gagnebina from northern Madagascar, G. bakoliae Luckow & Du Puy, is described and illustrated. The new species is most similar to G. bernieriana, and shares with it features such as resting buds, dehiscent fruits, and pollen in 16-celled polyads. Gagnebina bakoliae differs from G. bernieriana in having the pinnae decrescent both apically and basally, the petiole densely tomentose adaxially but glabrous abaxially, and pods somewhat larger and darker in color. Recent fieldwork in Madagascar by the authors has led to the discovery of a new species of Gagnebina. This genus is known from some six species, all of which are endemic to Madagascar and the nearby Comoros and Mascarene Islands. Traditionally circumscribed by indehiscent, winged fruits, Gagnebina was expanded by Lewis and Guinet (1986) to include any species with linear anthers. This involved the reassignment of several species that had previously been included in the closely related genus Dichrostachys. Both genera have staminodial flowers at the base of the inflorescence and centers of diversity in Madagascar. Recent cladistic analyses by the first author (Luckow, 1995) indicated that Gagnebina should further expand to encompass all those species with linear or subulate stipules if it was to be monophyletic. Another character correlated with stipule morphology, and mentioned by Lewis and Guinet (1986), is lack of the brachyblasts that characterize species of Dichrostachys and Alantsilodendron. In contrast, the species of Gagnebina discussed herein possess resting buds with perules. This may characterize the genus as a whole, although further work is needed to demonstrate that resting buds are present in all species in the genus. Gagnebina bakoliae Luckow & Du Puy, sp. nov. TYPE: NW Madagascar. Antsiranana: Route Nationale 6, ca. 25 km NE of Ambilobe, near village of Ambilomagodro, close to Ankarana Massif, 49007'E, 13001'S, 220 m, 17 Nov. 1992, G. P Lewis, D. Du Puy & B. D. Schrire 2141 (holotype, K; isotypes, BH, P, TAN). Figure 1. Gagnebinae bernierianae (Baillon) Luckow similis, sed petiolo et rachide dorsaliter glabris, ventraliter tomentosis, pinnis in rachide non valide accrescentibus, fructibus 10 cm usque longis et atrobadiis, et antheris ovato-sagittatis diversa. Spindly shrub or small tree 2-5 m tall; young branches angled, pubescent on the edges with curly or spreading golden hairs; older branches terete, with smooth, mottled gray bark; brachyblasts absent, but resting buds present with 6 to 8 perulate scales, 5-6 x 1.5-2 mm, ovate, striate with raised nerves, glabrous, stramineous. Stipules dimorphic, those on the leaves formed just after the resting bud breaks oblong, 4-5 x 1.5-2 mm, acute apically, striate, stramineous, similar in color and texture to the resting bud scales, deciduous; stipules gradually becoming subulate distally on the branch, 69 x 0.5 mm, ? persistent, present on most flowering and fruiting branches. Leaves 6-12 cm long, the petiole, rachis, and pinnae adaxially tomentose with gray or stramineous hairs, abaxially glabrous, petiole 0.8-2 cm long, rachis (4)6-10 cm long; nectary 1.5 mm diam., sessile, crateriform, orbicular, borne between the proximal pair of pinnae, often between the terminal pair and sometimes between other pairs; pinnae (10)15 to 20(25) pairs per leaf, decrescent at both ends, 2--4 cm long, the axis usually forming a subulate point 1-2 mm beyond the insertion of the terminal pair of leaflets; leaflets 40 to 60(70) pairs per pinna, 2-3 X 0.35-0.5 mm, linear-falcate, acute, truncate-oblique basally, glabrous, sometimes ciliate, the nearly centric midvein visible on the dorsal surface. Peduncle 2-3 cm long, sparsely puberulent, in fruit becoming (2-)47 cm long, stout, woody; inflorescences axillary, one or, more frequently, two per node, each a congested spike of 40 to 75 flowers, 1-2 cm wide, the rachis 2.5-3 cm long, the proximal flowers sterile, the distal fertile. Bracteoles subtending each flower 1.5 mm long, carinate, linear, deciduous, ciliate, 1nerved. Sterile flowers 7 to 20 per inflorescence, calyx shallowly cupulate, 0.5-1 mm long, constricted at the base to form a minute pedicel, the 5 lobes NovoN 10: 220-223. 2000. This content downloaded from 157.55.39.185 on Thu, 26 May 2016 05:29:14 UTC All use subject to http://about.jstor.org/terms Volume 10, Number 3 2000 Luckow & Du Puy Gagnebina bakoliae from Madagascar 221