Reinterpretation of the nomenclatural type of Pseudobombax heteromorphum (Malvaceae, Bombacoideae) reveals an overlooked new species from Bolivia

Abstract In the course of a taxonomic revision of Pseudobombax Dugand, one of us (JGCS) frequently has observed herbarium specimens of Bombacoideae that comprise a mixture of different Angiosperm families. In particular, Pseudobombax heteromorphum (Kuntze) A. Robyns, a frequent name in checklists of the Bolivian flora, is based on type material of Bombax heteromorphum Kuntze that is clearly a mixture of Pseudobombax flowers and Tabebuia Gomes ex DC. (Bignoniaceae) leaves. We herein designate as the lectotype of Bombax heteromorphum the flowers of an herbarium sheet deposited in NY and as epitype a complete specimen (leaves, flowers, and fruit) in HUEFS. We consider Bombax heteromorphum to be a synonym of Pseudobombax longiflorum (Mart.) A. Robyns, a species widespread in Neotropical seasonally dry forest of Bolivia, Brazil, Paraguay, and Peru. Furthermore, we describe a new species, Pseudobombax pulchellum Carv.-Sobr., apparently endemic to seasonally dry tropical forest (SDTF) in Bolivia (Chiquitano dry forest), based on specimens commonly but incorrectly identified as Pseudobombax heteromorphum.We also comment on the morphology, distribution, and conservation status of this new species.


Introduction
In his revision of Bombax L. s.l. , Robyns (1963) transferred B. heteromorphum Kuntze to Pseudobombax Dugand and considered P. heteromorphum (Kuntze) A.Robyns to be endemic to Bolivia. Based solely on the holotype of B. heteromorphum ( Kuntze s.n. , Fig.  1), Robyns described P. heteromorphum as having long petiolules and scarcely expanded petiole apices. In his key to the species of Pseudobombax , he used these two characters to separate this species from morphologically closely related congeners. According to Robyns's description, P. heteromorphum also has grooved (canaliculate) petiolules, which if true would represent a unique character in the genus Pseudobombax .
In the course of a taxonomic revision of Pseudobombax (Carvalho-Sobrinho, in prep.), mixed collections of Bombacoideae, including type specimens based on mixtures, often have been observed. Th is is especially common for collections from seasonally dry Neotropical forest habitats where species often are leafl ess during the fl owering period. In the present case, a careful examination of the morphology of the leaves and fl owers of the holotype of Bombax heteromorphum revealed that the specimen is a mixture of reproductive and vegetative elements from two diff erent Angiosperm families. Robyns (1963) failed to note that his type specimen has leafl ets that are articulated with the petiole, a character state unknown in Pseudobombax ; the genus is separated from all other Bombacoideae by the synapomorphy of non-articulated leafl ets, which lack an abscission zone between the apex of the petiole and the base of the petiolules (Robyns 1963, Carvalho-Sobrinho andQueiroz 2011) .
Th e holotype of Bombax heteromorphum (NY) and an image of an isotype (B as F negative 9535; Field Museum 2012) show fl oral material matching that of Pseudobombax longifl orum (Mart.) A.Robyns, including an androecium with a glabrous, relatively long staminal tube, fi laments freely originating from the apex of the tube (i.e., without phalanges), and typical hippocrepiform anthers. However, the vegetative material of these two type specimens matches the leaves of Tabebuia aurea (Silva Manso) Benth. & Hook. f. ex S. Moore (Bignoniaceae), with suberous branches, opposite leaves (inferred from leaf scars), longer and grooved petiolules, leafl ets with a clear abscission zone, and a clearly diff erent venation pattern (Fig. 1). Pseudobombax longifl orum, a species widespread in Neotropical seasonally dry forest of Bolivia, Brazil, Paraguay, and Peru, and T. aurea are sympatric in the Bolivian Chiquitano dry forest and the latter species has been collected several times in the type locality of B. heteromorphum (municipality of Velasco, Santa Cruz, Bolivia) according to Tropicos (2012) and specimen labels from herbaria (F, US, and WIS).

Pseudobombax pulchellum
Distribution. Pseudobombax pulchellum is known from only four sites in the Department of Santa Cruz, Bolivia, and appears to be endemic to Chiquitano dry forest at elevations of 230 to 520 m.
Phenology. Flowers of this new species are known from a single collection made in June; fruiting material was collected in October.
Etymology. Th e specifi c epithet refers to the small, delicate leafl ets and long, slender petiolules of this species, diagnostic even in sterile specimens. Th e epithet also honors the Brazilian botanist Aline Costa da Mota for her important insights and collaboration on the systematics of Bombacoideae.
Conservation status. Although Pseudobombax pulchellum occurs in the Kaa-Iya del Gran Chaco National Park, it must be considered Near Th reatened because it is known from only four sites and "there are plausible events that may cause the species to decline, but these are unlikely to make the species Extinct or Critically Endangered in a short time" (IUCN 2010). Extensive fi eldwork in other areas of dry forests in Bolivia is necessary to properly survey and to assess the status of this species. Discussion. Pseudobombax pulchellum is a remarkable species by its diminutive aspect, especially the relatively small, retuse, obovate to suborbicular leafl ets, and the fl owers; the petiolules are markedly long in relation to the petiole, and fruits are conspicuously acuminate. It seems to be closely related to P. longifl orum (Mart.) A. Robyns, a sympatric congener in Bolivian Chiquitano dry forest. Th e two are similar because of their glabrous aspect, long petiolules, leafl ets with retuse apices, truncate to cordate bases, and maculate seeds. Th e new species is also similar to Pseudobombax croizatii A. Robyns and P. minimum Carv.-Sobr. & L.P. Queiroz; both of these species share small fl owers (60-65 mm long), glabrous staminal tubes, androecia with relatively few stamens (c. 150-200), and glabrous fruits. Th e following key can be used to separate these four species of Pseudobombax.