Tigridiopalma exalata, a new and endangered species of Melastomataceae from China

Abstract A new species of the genus Tigridiopalma, formerly considered monotypic, is here described as T. exalata and illustrated based on molecular and morphological evidence. It is morphologically similar to T. magnifica in having a short stem, huge basal leaves, scorpioid cymes, and 5-merous flowers, but differs in having ribbed and pale yellow puberulent petioles, purple petals with a small white apical patch, connectives of longer stamens with a distinct dorsal short spur at their base, and wingless capsules. Due to the restricted distribution, small populations and horticultural potential of this new species, it should be categorized as an Endangered species (EN).

Tigridiopalma magnifica is only found in the Western Guangdong presently (Gaozhou, Xinyi and Yangchun, Fig. 1) (Chen and Renner 2007;Li et al. 2009;Ren et al. 2012). Due to its restricted distribution and small populations, it was categorized as an Endangered species (EN) in the latest version (2013) of the IUCN Red List of China and the Threatened Species List of China's Higher Plants (Qin et al. 2017).
Here we describe a new species of Tigridiopalma, T. exalata S.Jin Zeng, Y.C.Xu & D.F.Cui, from Eastern Guangdong, China. It can be easily distinguished from T. magnifica by having ribbed and pale yellow puberulent petioles (vs. not ribbed and reddish hispid), purple petals with a small white apical patch (vs. dark red petals with a large white apical patch), connectives of longer stamens with a distinct dorsal short spur at the base (vs. indistinct) and wingless (vs. narrowly winged) capsules. We also provide a phylogenetic analysis confirming that the new species belongs to Tigridiopalma.

Materials and methods
The morphological data collected for the species described here are based on living plants and specimens collected in the field. Voucher specimens were deposited at the herbaria CANT, IBSC, KUN and PE (acronyms according to Index Herbariorum in Thiers 2021).
We collected and sequenced the specimen (S.Jin Zeng 397) and then built a phylogenetic hypothesis with other sequences gathered from Genbank. Total genomic DNA was extracted from fresh material using a modified CTAB procedure (Smith et al. 1991). One nuclear DNA region (internal transcribed spacer, nrITS) and two plastid DNA markers (ndhF and rpl16) were used in this study following by Zeng et al. (2016).
To determine the phylogenetic position of the new species in the Sonerileae clade, 45 species from 22 genera (including 2 species of Tigridiopalma) were used for molecular analyses (Suppl. material 1: Table S2). Dissochaeta vacillans Blume and Pseudodissochaeta lanceata Nayar were selected as outgroup taxa based on Zhou et al. (2019b). Maximum likelihood (ML) analysis was performed by RAxML-HPC2 on XSEDE (Stamatakis 2014) through the CIPRES portal (Miller et al. 2010) using GTRCAT model and 1000 bootstraps.

Results
The aligned sequence matrix contained 2694 characters. Summary features of sampled sequences are summarised in Suppl. material 1: Table S3. The phylogenetic analysis indicated that the genus Tigridiopalma is recovered sister to Scorpiothyrsus plus Tashiroea clade (BS ML 26), and the new species is sister to Tigridiopalma magnifica with strong support (BS ML 100) (Fig. 2).
A detailed comparison of this new species and T. magnifica is shown in Table 1.

Zeng et al. (2016) first investigated the phylogenetic position of Tigridiopalma by using four makers (nrITS, ndhF, rbcL and rpl16) and found that it was close to Sonerila
Roxb. and Tashiroea with moderate support (BS ML 73). Subsequently, more taxa were added to reconstruct the phylogeny of Sonerileae with two markers (nrITS and trnV-trnM spacer), which indicated that Tigridiopalma was sister to Medinilla with weak support (BS ML 49) (Zhou et al. 2019a). Subsequent phylogenomic analyses of Sonerileae using 171 plastid genomes showed that Tigridiopalma is sister to the clade consisting of Driessenia, Heteroblemma, Medinilla and some species of Phyllagathis with moderate support (BS ML 71) (Zhou et al. 2019b). Due to the highly structurally conserved plastomes of Melastomataceae (Reginato et al. 2016;Zhou et al. 2019b), more nuclear DNA makers or SNPs are required to resolve the generic relationships of Sonerileae, including the closest relatives of Tigridiopalma. Diagnosis. The new species Tigridiopalma exalata resembles T. magnifica in having a short stem, huge basal leaves, scorpioid cymes, and 5-merous flowers, but differs in its ribbed and densely pale yellow puberulent petioles, connectives of longer stamens with a distinct dorsal short spur at their base, and wingless capsules.
Phenology. Flowering in October-November, fruiting in January-March. Etymology. The specific epithet combined from ex-(lacking) and alatus (winged) which refers to the wingless capsules. Vernacular name. Hui Zhou Hu Yan Hua (Chinese pronunciation); 惠州虎颜花 (Chinese name).
Distribution. Tigridiopalma exalata grows in damp, shaded but well-drained places in broad-leaved forests, in elevations between 100 m and 350 m in Huizhou, Guangdong Province, China (Fig. 4).
Preliminary conservation assessment. About 1000 mature Tigridiopalma exalata individuals from one locality have been found in less than 60 km 2 up to now. This area can be classified as the extent of occurrence. The plants are not well protected in a Forest Park and the populations are severely fragmented. This species has horticultural potential as an ornamental plant. According to the IUCN Standards and Petitions Committee (2019), a category of Endangered (EN) is recommended for Tigridiopalma exalata for the present.