A new species of Fordiophyton (Sonerileae, Melastomataceae) from Yunnan, China

Abstract Fordiophytonjinpingense (Melastomataceae; Sonerileae), a species occurring in south-eastern Yunnan, China, is described as new, based on morphological and molecular data. Phylogenetic analyses, based on nrITS sequence data, showed that, except F.breviscapum, all species sampled in Fordiophyton formed a strongly supported clade in which two geographical lineages were recovered. The generic placement of F.jinpingense is well supported by phylogenetic analyses and a character combination of 4-merous flowers, distinctly dimorphic stamens and the connectives basally not calcarate. Molecular divergence and morphological evidence indicate that F.jinpingense is well separated from other members of the genus, thus justifying its recognition as a distinct species. Fordiophytonjinpingense is phylogenetically closest to F.repens, but differs markedly from the latter in stem morphology (short, obtusely 4-sided vs. long, 4-angular), habit (erect vs. creeping), leaf size (6–16.5 × 4.5–13 cm vs. 4–7.5 × 4–6.5 cm) and flower number per inflorescence (5–13 vs. 3–6).


Introduction
In the study of Asian Sonerileae, Stapf established two new genera, Fordiophyton Stapf and Gymnagathis Stapf, based on three species in China (Stapf 1892). Both genera were accepted by subsequent authors (Krasser 1893;Diels 1932;Li 1944;Chen 1984a, b). Li (1944) pointed out that Gymnagathis is an illegitimate generic name and proposed a new name Stapfiophyton Li to replace it. However, Hansen (1992) considered the type species of Stapfiophyton, S. peperomiifolium (Oliver) H. L. Li, to be similar to Fordiophyton and therefore placed Stapfiophyton in synonymy under Fordiophyton. Hansen's treatment was thereafter adopted by other authors (Deng and Wu 2004;Chen and Renner 2007).
Fordiophyton, as currently defined, is a small Asian genus of 13 species mainly occurring in southern China, with only one species extending to northern Vietnam (Chen and Renner 2007;Ning and Liu 2010;Zeng et al. 2016a, b). It is characterised by 4-merous flowers, eight unequal stamens, distinctly dimorphic anthers, connectives not calcarate at the base and anther base of longer stamens not forked, obtusely forked or forked and curved (Fig. 1). Ten species of Fordiophyton have been included in previous molecular phylogenetic studies (Zeng et al. 2016a, b;Zhou et al. in press). Amongst the species sampled in Fordiophyton, F. breviscapum (C. Chen) Y. F. Deng & T. L. Wu appeared to be close to Phyllagathis tetrandra Diels and P. elattandra Diels (Zhou et al. in press), while the remaining species, including the type species, F. faberi Stapf, formed a well-supported clade close to Blastus, Bredia-Phyllagathis clade 2 and Plagiopetalum (Zeng et al. 2016a, b;Zhou et al. in press).
During a field survey, we encountered a distinct plant in the forests of Ma-an-di, Fenshuiling National Nature Reserve in Jinping County, south-eastern Yunnan. This plant had eight distinctly dimorphic stamens and connectives not calcarate at the base, which are typical characteristics of Fordiophyton. It was distinct from all known species of Fordiophyton in the combination of short stems with distinct internodes, basal rosette of leaves, unwinged, densely villous petioles, umbellate inflorescence and anther base of longer stamens distinctly forked and curved (Figs 2, 3). We suspected that it represented an undescribed species. To evaluate the specific status and phylogenetic position of this species in Fordiophyton, phylogenetic analyses were performed, based on DNA sequence data of the nuclear ribosomal internal transcribed spacer (nrITS). The results confirmed our suspicions that these plants represented a previously unrecognised species, F. jinpingense, which we describe below as new. A key to separate it from other species of Fordiophyton is also provided.

Materials and methods
For phylogenetic analyses, the nrITS sequences of F. longipes and F. jinpingense were newly sequenced, while the sequences of other species were downloaded from Gen-Bank. The final dataset contained 131 accessions representing 106 species and three varieties from 19 genera in Sonerileae/Dissochaeteae and one in tribe Blakeeae. Blakea schlimii (Naudin) Triana was selected as an outgroup according to previous studies (Clausing et al. 2000;Clausing and Renner 2001;Renner et al. 2001;Goldenberg et al. 2012;Zhou et al. in press). In total, twelve species of Fordiophyton (85.7%) were sampled in the analyses. The source of the materials and GenBank accession numbers are given in Suppl. material 1.
Total DNA was extracted from fresh leaves using the modified CTAB procedure (Doyle and Doyle 1987). The nrITS region of F. longipes and F. jinpingense were amplified and sequenced using universal primers (White et al. 1990), following the procedure described in Zou et al. (2017).
Sequences were aligned using SeqMan v.7.1.0 (DNASTAR Inc., Madison, WI). The best-fitting nucleotide substitution model was determined using the Akaike Information Criterion in Modeltest version 3.7 (Posada and Crandall 1998) prior to phylogenetic analyses. The substitution model GTR+I+G was selected. Bayesian Inference (BI), Maximum Likelihood (ML) and Maximum Parsimony (MP) analyses were performed according to Zhou et al. (in press).

Results
The aligned sequence matrix contained 766 characters. Statistics of sequences sampled are summarised in Suppl. material 2. Trees generated by ML, MP and BI analyses were highly similar in topology, except that some nodes with weak support in ML analyses collapsed in MP or BI analyses. The tree resulting from ML analysis is shown in Suppl. material 3, with BI posterior probability (PP), ML bootstrap support values (BS) and MP bootstrap support values (PBS) labelled at nodes. As shown in Fig. 4, F. breviscapum, P. tetrandra and P. elattandra comprised a clade with weak support (PP = 0.72, BS = 42%, PBS = 49%), while the remaining 11 species formed the well-supported Fordiophyton clade (PP = 1.0, BS = 100%, PBS = 99%). The sister relationship of these two clades was only weakly supported in BI and ML analyses (PP = 0.19, BS= 15%). Two subgroups were recovered within the Fordiophyton clade with strong support. One

Phylogeny of Fordiophyton
Phylogenetic analyses recovered two subclades in the Fordiophyton clade (Fig. 4). The grouping of species shows weak correlation with morphology. Both subclades are quite variable in habit (short stem with a basal rosette of leaves/long and leafy stem) and morphology of the leaf blade (ovate, cordate to lanceolate), petiole (hairy/glabrous, winged/ unwinged) and inflorescence (umbellate/cymose paniculate). However, the subclades represent two geographic lineages. Six out of the seven species in subclade 1 are narrowly endemic to south-eastern China (Guangdong and Hongkong), whereas three out of the four species in subclade 2 are endemics of south-western China (Yunnan).
The currently circumscribed Fordiophyton is not monophyletic, as F. breviscapum appears to be related to Phyllagathis tetrandra and P. elattandra, rather than to other members of the same genus. Fordiophyton breviscapum is morphologically most closely related to F. degeneratum (C. Chen) Y. F. Deng & T. L. Wu, which was not included in the phylogenetic analyses. These two species, as well as P. tetrandra and P. elattandra, have been treated in Stapfiophyton (Li 1944;Chen 1984a, b). Interestingly, these four species share some common features, such as hypanthium distinctly 4-sided and the inner whorl of stamens greatly reduced (F. breviscapum), sterile (F. degeneratum and P. elattandra) or undeveloped (P. tetrandra) (Fig. 5). As the relationships amongst these species are only weakly supported, their generic placement remains unclear, pending further study.
Fordiophyton damingshanense S. Y. Liu & X. Q. Ning is another species which was not sampled in previous and present phylogenetic studies. It highly resembles F. faberi in habit, leaf morphology and stamen morphology. Geographically, it occurs in Guangxi, where F. faberi also occurs. Morphology and distribution imply that F. damingshanense is probably a member of subclade 1.

Phylogenetic position and specific status of F. jinpingense
The generic placement of F. jinpingense is supported by morphological and phylogenetic data. Its 4-merous flowers, eight distinctly dimorphic stamens and the connectives basally not calcarate fit perfectly well with the morphological circumscription of Fordiophyton. Phylogenetic analyses also showed that F. jinpingense was nested within the same clade, together with the type of Fordiophyton, F. faberi.
Phenology. Flowering March-April, fruiting April-May. Etymology. The specific epithet is derived from Jinping County, the type locality of Fordiophyton jinpingense.
Distribution. Fordiophyton jinpingense is currently known only from Jinping County, south-eastern Yunnan, China (Fig. 7). It occurs in dense or open forests, often in damp, shaded, but well drained places, such as on steep slopes, at 900-1900 m alt.