A new species of Goniothalamus (Annonaceae) from Palawan, and a new nomenclatural combination in the genus from Fiji

Abstract A new species, Goniothalamus palawanensis C.C.Tang & R.M.K.Saunders, sp. nov. (Annonaceae), is described from Palawan, Philippines. Goniothalamus palawanensis is most closely related to Goniothalamus amuyon (Blanco) Merr., but differs in its shorter inner petals, hairy ovaries, and funnel-shaped stigmas. A new nomenclatural combination, Goniothalamus angustifolius (A.C.Sm.) B.Xue & R.M.K.Saunders, comb. nov., is furthermore validated to reflect the phylogenetic affinities of a Fijian species previously assigned to Polyalthia.


Introduction
Th e Annonaceae are a species-rich early-divergent angiosperm family, consisting of ca. 108 genera and ca. 2500 species of trees, scandent shrubs and woody climbers , forming an important component of tropical lowland forest ecosystems. Th e genus Goniothalamus (Blume) Hook. f. & Th omson (subfam. Annonoideae Raf., tribe Annoneae Endl.) is one of the largest genera in the family, with more than 130 species (Nakkuntod et al. 2009). Th e genus is widely distributed in lowland and submontane forests of tropical South-east Asia, with a centre of diversity in western Malesia, particularly Borneo (34 species: Mat-Salleh 2001; Turner and Saunders 2008), Sumatra (14 species : Saunders 2002) and Peninsular Malaysia/Th ailand, south of the Isthmus of Kra (22 species : Saunders 2003;Saunders and Chalermglin 2008).
Goniothalamus species are small to large trees, with generally solitary, axillary and pendent infl orescences, and are often caulifl orous or ramifl orous. Individual fl owers possess one whorl of three sepals, and two whorls of three petals each, with the outer petals larger than the inner. Th e three inner petals form a distinctive mitriform dome over the reproductive organs, with three lateral apertures at the base of the dome allowing access to beetle pollinators (Saunders 2010(Saunders , 2012. Th e fl owers are hermaphroditic, with numerous free stamens and carpels. Th e stamens have broad connectives that cover the thecae; these connectives vary in length and are taxonomically important. Th e carpels are variable in ovary indument and the size and shape of the stigmatic head. Th e fruits are apocarpous, with "monocarps" (derived from individual carpels after fertilisation) that are either sessile or borne on stipes.
Fieldwork in Palawan has revealed a previously unknown Goniothalamus species, which is formally described here as G. palawanensis C.C.Tang & R.M.K.Saunders. Th e present research also validates a new nomenclatural combination arising from the transfer to Goniothalamus of a Fijian species that was formerly classifi ed in Polyalthia . Diagnosis. Similar to Goniothalamus amuyon (Blanco) Merr. except with shorter inner petals (11-16 mm), hairy ovaries, and fi liform pseudostyles with funnel-shaped stigmas.
Phenology. Flowering specimens collected in May and June; fruiting specimens unknown.
Etymology. Th e specifi c epithet refl ects the geographical distribution of the species in Palawan.
Th e fl ora of Palawan shows close biogeographical affi nities with Borneo, refl ecting the extensive connectivity that existed between the two regions (Hall 2009). Two of the species listed above as close relatives of G. pala wanensis occur in Borneo, viz. G. rufus and G. velutinus . In addition to the diff erences in leaf and sepal venation alluded to above, these species diff er from G. palawanensis in possessing greatly enlarged and warty pseudostyles/stigmas (Mat-Salleh 1993).
IUCN conservation status. EN B1ab(iii) (IUCN, 2001). Goniothalamus palawanensis is endemic to Palawan, with an extent of occurrence of ca. 1,800 km 2 . Th e species is only known from three periods of collection (1950, 1984 and 2012), and from fewer than fi ve localities. Th e region is subject to continuing habitat decline due to logging of low altitude forests (DENR/UNEP 1997), hence the endangered red list category recommendation. Discussion. Th e historical delimitation of the genus Polyalthia has been shown to be highly polyphyletic, and large-scale taxonomic realignment and recognition of new genera has been undertaken to ensure strict monophyly of genera (Mols et al. 2008;Saunders et al. 2011;Xue et al. 2011Xue et al. , 2012Chaowasku et al. 2012). As part of this series of taxonomic revisions, chloroplast DNA regions were sequenced from eight species from the Melanesian island of Fiji (Xue, 2013) that had previously been assigned to Polyalthia . Phylogenetic analysis of this data revealed that most of these species align with either Hubera (Chaowasku et al. 2012;Xue 2013) or Meiogyne (Xue 2013;Xue et al. in press), although one species, Polyalthia angustifolia A.C.Sm., which was sequenced from the type material, is nested within the Goniothalamus clade (Xue 2013). Polyalthia angustifolia was originally described from fruiting material (Smith 1943), and it is likely that its incorrect generic affi liation was due to the absence of fl owers, which are very different in Polyalthia and Goniothalamus . Subsequent phylogenetic analyses with a larger taxon sampling (C.C. Tang et al., unpubl.) have revealed P. angustifolia as sister to the Fijian species Goniothalamus monospermus (Baill.) R.M.K.Saunders with strong support (posterior clade probability = 1; bootstrap support = 96%); these two species are morphologically distinct, as P. angustifolia seeds lack the broad lateral testa wings that are diagnostic of G. monospermus (Van Setten and Koek-Noorman 1992: pl. 39i). Th e transfer of the name P. angustifolia to Goniothalamus is accordingly validated here.