Nesogordonia tricarpellata (Dombeyaceae), a new species from Madagascar that compels modification of the morphological circumscription of the genus

Abstract Nesogordonia tricarpellata Skema & Dorr, sp. nov., a new species from southeastern Madagascar, is described and illustrated. It differs from all other species of Nesogordonia Baill. in having 6–9 stamens, 3 staminodes, a 3-carpellate ovary, and a 3-valved capsule. These androecial and gynoecial characters require modification of the long-standing circumscription of the genus. The new species also has the southernmost geographic range of any species in the genus.


Systematics
Distribution. Endemic to southeastern Madagascar, where it is known from two collections made in Parcelle 1 of the Parc National d'Andohahela (formerly Réserve Naturelle Intégrale d'Andohahela) and one on the lower slopes of the Ivohibe-Bemangidy forest (Fig. 2).
Ecology. Evidently restricted to humid forest from 90-500 m. Flowering specimens were collected in February (fl oral buds) and June (mature fl owers). A fruiting specimen was collected in June.
Etymology. Th e epithet was chosen to highlight the fact that the gynoecium of this species is 3-carpellate.
Conservation status. At present, this species is known from three collections and two localities, only one of which is protected (Parc National d'Andohahela). Based on this and estimates of an extent of occurence < 100 km 2 and an area of occupancy < 10 km 2 , Nesogordonia tricarpellata is assigned a preliminary status of Critically Endangered (CR B1ab(i-iv) + B2ab(i-iv)) following the criteria and categories of the IUCN ( Discussion. We have no doubt that this new species belongs in Nesogordonia as it has the fruit and seeds unique to the genus: an obovoid woody capsule containing seeds with long, basal wings (Fig. 1I). Nesogordonia tricarpellata is remarkable in having an androecium comprised of 6-9 stamens in an outer whorl and 3 staminodes in an inner whorl; a 3-carpellate ovary; 3 style branches and 3 stigma lobes; and a 3-valved capsule (Fig. 1E, G). While the number of stamens is variable in other species of Nesogordonia, the outer whorl typically possesses some multiple of fi ve (usually 10-25 total) stamens and the inner whorl possesses either 5 free staminodes (most species) or 5 stamens (N. abrahamii L.C. Barnett, N. ambalabeensis Arènes, and N. fertilis H. Perrier). All other species of Nesogordonia have 5-carpellate ovaries, 5 style branches, 5 stigma lobes, and 5-valved capsules. Although the parts of the androecium and gynoecium of N. tricarpellata are reduced in number, the fl owers of the new species are 5-merous with 5 calyx lobes and 5 petals, which also is characteristic of all other species of Nesogordonia (Fig. 1D).
Nesogordonia tricarpellata is the only species in the genus with lepidote scales on the ovary (Fig. 1H, I). All other species of Nesogordonia have stellate hairs on the ovary (Barnett 1988). As has been noted before (Jenny et al. 1999, Dorr 2001), a number of other genera in the Dombeyaceae have species with either stellate hairs or lepidote scales on the ovary, including Dombeya, Harmsia K. Schum., and Helmiopsis.
Nesogordonia tricarpellata most closely resembles N. micrantha Arènes. Th e two species have similar leaf shape, size, and vestiture; infl orescence morphology; and fl oral bud shape. Th e leaf blades of both species are glabrous to sparingly pubescent with domatia of tufted hairs in the axils of the 1° and 2° veins below. Th e leaves of N. micrantha, however, are elliptic to obovate (versus elliptic to narrowly elliptic), 2.2-5 × 1.1-2.8 cm (versus 5-7.5 × 2.5-3 cm), apically acute (versus long acuminate), and the margin is undulate to slightly crenulate (versus slightly crenulate). Both species have (1-) 2-3-fl owered axillary, paniculate cymes and globose fl oral buds. Th e fl oral buds of N. micrantha, however, are densely (versus sparingly) stellate pubescent. In addition, the two species have non-overlapping geographical ranges; N. tricarpellata appears to be restricted to the Anosyenne Mountains in southeastern Madagascar while N. micrantha is known only from western Madagascar having been collected principally in the Forêt d'Antsingy.
Th e geographical distribution of Nesogordonia tricarpellata also is remarkable as the species has the southernmost distribution of any species in the genus. Nesogordonia tricarpellata appears to be restricted to humid forest on the eastern slopes of the Anosyenne Mountains in extreme southeastern Madagascar south of the Tropic of Capricorn (Fig. 2). Th e Parc National d'Andohahela includes the southernmost moist "tropical" forest in Madagascar, a forest that appears to be an extension of the humid montane forest common to the north but found at lower elevations in the Anosyenne Mountains (Goodman 1999).
Sequence data for one nuclear ribosomal (ITS) and fi ve noncoding plastid markers have been gathered for Nesogordonia tricarpellata as part of an ongoing phylogenetic study of Dombeyaceae (Skema in prep.). Parsimony analysis of these data group this new species with N. humbertii Capuron (Randrianaivo et al. 1391), the only other species of Nesogordonia sampled, with high support (bootstrap = 100% from 10,000 replicates).