A revision of the Dombeya rigida complex (Malvaceae) Wendy L. APPLEQUIST Missouri Botanical Garden, P. O. Box 299, St. Louis, MO, 63166-0299 (USA) [email protected] Applequist W. L. 2011. — A revision of the Dombeya rigida complex (Malvaceae). Adansonia, sér. 3, 33 (2): 249-262. DOI: 10.5252/a2011n2a10. ABSTRACT A revision of Dombeya subsect. Rigidae, which comprises two Malagasy species (D. linearifolia and D. rigida), is presented. Th e classifi cation of these species within Dombeya is preferred to an alternate placement within Helmiopsis. Th ree subspecies of D. rigida are recognized: subsp. parvifolia, characterized by small leaves, is newly described, and subsp. guazumifolia is newly recognized at that KEY WORDS rank. Arènes’ two subspecies of D. linearifolia are synonymized, and a new Malvaceae, subsp. muricata, characterized by fruit similar to that of D. rigida, is described. Dombeya, Both species display considerable variation in leaf and fruit morphology in the Helmiopsis, Madagascar, north, but variation is discontinuous, indicating that the species are usually new subspecies. reproductively isolated. RÉSUMÉ Une révision du complexe Dombeya rigida (Malvaceae). Une révision de Dombeya subsect. Rigidae, qui comprend deux espèces malgaches (D. linearifolia et D. rigida), est présentée. L’attribution de ces espèces au genre Dombeya est préférée à l’attribution alternative au genre Helmiopsis. Trois nouvel- les sous-espèces de D. rigida sont reconnues : subsp. parvifolia, qui se caractérise par des feuilles petites, est nouvellement décrite, et subsp. guazumifolia est nou- vellement reconnue à ce niveau. Deux sous-espèces de D. linearifolia proposées MOTS CLÉS par Arènes sont mises en synonymie, mais une nouvelle subsp. muricata, qui Malvaceae, se caractérise par un fruit semblable à celui de D. rigida, est décrite. Les deux Dombeya, espèces présentent une variabilité considérable de la morphologie des feuilles Helmiopsis, Madagascar, et des fruits dans le nord, mais la variation est discontinue, ce qui indique que sous-espèces nouvelles. les espèces sont normalement isolées génétiquement. ADANSONIA, sér. 3 • 2011 • 33 (2) © Publications Scientifi ques du Muséum national d’Histoire naturelle, Paris. www.adansonia.com 249 Applequist W. L. INTRODUCTION ducous bracteoles, or small patches of glandular tissue inside the sepal bases (also observable in many Dombeya rigida Baill. and D. linearifolia Hochr. are Dombeya species [Vogel 2000; pers. obs.]). Its scor- two of nine species of Dombeya Cav. (Malvaceae s.l.; pioid infl orescences and dense stellate pubescence cf. Bayer et al. 1999) that Hochreutiner’s (1926) throughout, though not seen elsewhere in Helmi- treatment placed in sect. Capricornua Hochr., opsis, are shared by other species of Dombeya sect. which is characterized by two- to several-branched, Capricornua. Stamen position appears to be more cymose infl orescences with scorpioid branches. variable within both genera than has been previ- Hochreutiner (1926) noted that D. rigida was ously recognized; some variation within D. rigida “remarquable à cause de ses pétales glanduleux itself and in other Dombeya species can be observed, à la base”. In the next and most recent complete whereas members of Helmiopsis sect. Glandulip- treatment of Malagasy Dombeya, Arènes (1958, etalae usually have more or less oppositipetalous 1959) divided sect. Capricornua into subsect. stamens, in contrast to most of sect. Helmiopsis. Rigidae Arènes, limited to D. rigida and D. lin- Finally, it is not clear that the very narrow curved earifolia and characterized by papillose glands on marginal wing observed by Dorr (2001) is ho- the basal portion of the adaxial petal surface, and mologous with the greatly elongated apical wing of subsect. Greveanae Arènes, comprising seven spe- Helmiopsis; Dombeya linearifolia, whose placement cies without petal glands, including fi ve previously he did not address but which is almost certainly recognized in sect. Capricornua by Hochreutiner. the sister species of D. rigida, has unwinged seeds. Th e two species of subsect. Rigidae have numer- Dombeya rigida has therefore been excluded from a ous characters in common, being distinguished recent treatment of Helmiopsis (Applequist 2009). largely by leaf size and shape and traditionally by Th e systematics of Dombeya and related genera are the degree of ovary lobing, and are undoubtedly messy, and Dombeya may be paraphyletic with re- closely related. spect to several smaller genera, including Helmiopsis Dorr (2001) transferred Dombeya rigida to (Le Péchon et al. 2009, 2010). Until the relation- Helmiopsis H.Perrier, as he felt that the species ships within this group are resolved by molecular was improperly placed in Dombeya. He observed analyses including more taxa (now in progress; C. that the seeds of D. rigida were laterally fl attened Skema, pers. comm.), it seems most conservative with a narrow curved dorsal wing. According to to leave species of uncertain affi nities in a broadly Arènes’ (1959) treatment of Malagasy Sterculiaceae, circumscribed Dombeya. However, examination winged seeds, combined with a coronate rather of material of both D. rigida and D. linearifo- than fasciculate androecium, oppositipetalous lia indicated that the range and distribution of staminodes and oppositisepalous stamens, and morphological variation in these species was not glabrous locules, would place this species in the adequately represented by the specimens available genus Helmiopsis H.Perrier, a Malagasy endemic to Arènes (1959), who published the last complete with previously nine species recognized. Most spe- treatment. An updated treatment of these species cies of Helmiopsis have elongated apical seed wings, is therefore made available here. and four species, those placed within Helmiopsis sect. Glandulipetalae Arènes, have similar glandular GEOGRAPHY AND CONSERVATION petals and stamens shorter than the staminodes Geographic distribution ranges from northern to (the latter being a very common state in Dombeya western and southwestern Madagascar. Dombeya as well). linearifolia is confi ned to the extreme north; Dorr’s (2001) placement of Dombeya rigida D. rigida is widespread and found on a variety of within Helmiopsis seems no less awkward than its substrates, although two of the subspecies herein placement within Dombeya. Th e species does not recognized have narrower ranges and perhaps possess other features characteristic of Helmiopsis, more selective habitat requirements. Specimen such as lepidote indument, small and rapidly ca- locality data were analyzed to provide preliminary 250 ADANSONIA, sér. 3 • 2011 • 33 (2) Dombeya rigida complex (Malvaceae) estimates of conservation status according to the fi laments. While Malagasy species of Dombeya IUCN Red List Categories and Criteria (IUCN have generally been described as hermaphroditic, 2001). For most included taxa, at least fi ve separate some species native to the Mascarene Islands have localities have been recorded and the preliminary been reported to display both cryptic and leaky, estimate of conservation status is Least Concern or inconsistent, dioecy (Humeau et al. 1999a, (LC). However, Dombeya linearifolia subsp. lin- b), raising the possibility that a similar condition earifolia is known from only three localities in might also be present, overlooked, in Malagasy relatively close proximity to one another (two of species. While material of subsect. Rigidae is too which possibly represent the same population); limited to rule out the possibility of leaky dioecy, it is therefore provisionally assessed as Vulnerable a number of fl owering specimens are observed to (VU D2). produce both pollen and ovules within the same fl ower. MORPHOLOGY Fruit morphology is a critical yet confusing Dombeya rigida and D. linearifolia resemble one character in subsect. Rigidae. Dorr (2001) dis- another in most characters, including distinctive covered that D. rigida at maturity has unusual features such as scorpioid-branched infl orescenc- ribbed, strongly muricate capsules with margin- es and the presence of petal glands, the latter of ally winged seeds (the wing is shallow or, in some which is otherwise unknown in Dombeya. Th e two fruiting specimens, reduced to an inconspicuous are distinguished primarily by leaf morphology dorsal ridge). While one subspecies of D. lineari- (size, shape, and relative petiole length). Dombeya folia also has fruits of this type, the other has a rigida has ovate to narrowly ovate, oblong-ovate, smaller, deeply lobed, smooth-surfaced fruit; seeds or oblong-lanceolate leaves, often with relatively have shallow or no marginal ridges. Th e northern long petioles, whereas D. linearifolia has much subspecies of D. rigida whose leaves appear most narrower, oblong to lanceolate, short-petioled similar to those of to D. linearifolia, rather than leaves. Most specimens of both species, including having an intermediate fruit type, usually has an all subspecies herein recognized, have domatia, extreme version of the muricate fruit type with which within a taxon may be roofed or cleft with elongated, acute papillae. However, one speci- clusters of straight hairs, in axils of the lower lat- men has fruits that, while not fully mature, are eral veins of large leaves. Domatia are uncommon not muricate. in most subgroups of Dombeya, though they have previously been reported in a few species of subg. Xeropetalum (Del.) K. Schum., sect. Xeropetalum MATERIAL AND METHODS (Arènes 1958; Seyani 1991) and are