Perilimnastes is a genus currently treated in the polyphyletic Phyllagathis. Recent phylogenomic analyses have identified a morphologically cohesive lineage referred to as the Phyllagathis (raphides) clade, which should be excluded from Phyllagathis and treated as a distinct genus under the name Perilimnastes. Morphological and phylogenomic data have confirmed that four new species collected from Vietnam are part of the Phyllagathis (raphides) clade. They are described herein as Perilimnastes multisepala, P. setipetiola, P. uniflora, and P. banaensis. Perilimnastes multisepala is phylogenetically closest to Phyllagathis setotheca, and morphologically to P. fruticosa and P. stenophylla, but is distinct in the 4- to 8-lobed calyx, 28 × 9 mm, apically long acuminate petals, and 1–2 mm pedicel at fruiting stage. Perilimnastes setipetiola, P. uniflora, and P. banaensis are phylogenetically most closely related. Perilimnastes uniflora is characterized by its prostrate habit, small size, glabrous, obovate to obovate-lanceolate leaf blade, and solitary flower. Perilimnastes setipetiola and P. banaensis resemble each other in habit, leaf size and shape, and sessile or near sessile inflorescences but can be easily distinguished by the indumentum of the stems and leaves.

Melastomataceae, Perilimnastes, Phyllagathis, taxonomy

Perilimnastes Ridl. was established based on P. fruticosa (Ridl.) Ridl. (Ridley 1918, 1922), a species originally published in Anerincleistus Korth. as A. fruticosus Ridl. (Ridley 1908). Perilimnastes fruticosa is characterized by its shrubby habit, subcoriaceous 3-veined leaves, few-flowered cymes, isomorphic stamens, and crowned capsules. It grows on rocks along streams in forests. Ridley (1918) noted that the fruit of P. fruticosa (=A. fruticosus) did not fit into any existing genera and described it as a distinct genus named Perilimnastes. Nayar (1974) accepted Ridley’s concept of Perilimnastes and described a second species, P. rupicola M.P.Nayar, which resembles P. fruticosa in habit and morphology of leaves, calyx lobes, stamens, and capsules. However, subsequent authors didn’t recognize Perilimnastes. Maxwell (1982, 1989) synonymized Perilimnastes and accommodated its two members in Anerincleistus sect. Coriaceae Ridl. (as A. fruticosus) and sect. Anerincleistus [as A. rupicola (Nayar) J.F.Maxwell], respectively. On the other hand, Cellinese (2002, 2003) placed both species within the broadly defined Phyllagathis Blume [as P. fruticosa (Ridl.) C.Hansen ex Cellin. and P. rupicola (M.P.Nayar) C.Hansen ex Cellin., respectively].

The classification of Asian Sonerileae at generic level has been a topic of ongoing controversy, particularly regarding the delimitation of Phyllagathis and various genera morphologically related to it (Diels 1932; Li 1944; Chen 1984a, b; Hansen 1992; Cellinese and Renner 1997; Cellinese 2002, 2003; Chen and Renner 2007). A series of molecular phylogenetic analyses consistently demonstrated the polyphyletic nature of Phyllagathis (Zeng et al. 2016; Zhou et al. 2018; Zhou et al. 2019a, b, c; Liu et al. 2022; Zhou et al. 2022). Zhou et al. (2022) presented the first well-resolved phylogeny of Asian Sonerileae and identified 34 major clades based on genome-scale data. Species currently treated in Phyllagathis were found in 17 lineages scattered across Asian Sonerileae. The type of Phyllagathis showed no close relationships with other members and the genus may have to be redefined as monotypic. Samples of Anerincleistus formed a strongly supported clade with certain Bornean species of Phyllagathis. The generic type of Perilimnastes, namely P. fruticosa (also known as Phyllagathis fruticosa and Anerincleistus fruticosus), was not included in the analyses. Nonetheless, species closely resembling P. fruticosa, such as Phyllagathis stenophylla (Merr. & Chun) H.L.Li and Phyllagathis suberalata C.Hansen, were recovered as part of the Phyllagathis (raphides) clade, which consists of members characterized by a fruticose/suffruticose growth habit, cuneate to rounded leaf base, umbellate or cymose inflorescences sometimes sessile or reduced to a single flower, isomorphic stamens, crowned capsules, horned placental column, thready placentas, as well as the presence of raphide crystals in some species. Based on these diagnostic characteristics and notable similarity observed between sampled and unsampled species, Zhou et al. (2022) concluded that the Phyllagathis (raphides) clade should contain approximately 20 species distributed in southernmost China, Vietnam, the Malay Peninsula, and Borneo. Given its distant relationship with the generic type of Phyllagathis, this clade justifies recognition as a distinct genus. As compelling morphological evidence indicates that the type of Perilimnastes (P. fruticosa) is a member of the Phyllagathis (raphides) clade, Perilimnastes should be resurrected as its generic name (Zhou et al. 2022).

During a field expedition in Vietnam, four species that were previously unrecorded in the Flora of Vietnam were collected from Đại Lộc, Quảng Nam Province (1 sp.), Đà Lạt, Lâm Đồng Province (1 sp.), and Hòa Ninh, Đà Nẵng (2 spp.) (Fig. 1). These plants share strong morphological resemblance to Perilimnastes [= the Phyllagathis (raphides) clade] and their placement within this clade was later confirmed through phylogenomic analyses conducted by Zhou et al. (2022). Morphological comparison between the four plants and their possible relatives revealed that they represent species new to science, which we described below as Perilimnastes multisepala J.H.Dai, T.V.Do & Ying Liu (Figs 2–4), P. setipetiola J.H.Dai, T.V.Do & Ying Liu (Figs 5, 6), P. uniflora J.H.Dai, T.V.Do & Ying Liu (Figs 7, 8), and P. banaensis J.H.Dai, T.V.Do & Ying Liu (Figs 9, 10).

Figure 1. 

Distribution of Perilimnastes multisepala (triangle), P. setipetiola (square), and P. uniflora and P. banaensis (solid circle).

Morphological and distribution data were obtained through field, herbarium and literature surveys as well as observation of living plants in the facilities of Sun Yat-sen University. Specimens of the species concerned (GXMI, IBSC, IBK, KUN, PE, SYS) or their high-resolution photos (A, BM, C, E, G, K, NY, P, US) were examined. Species delimitation followed Chen (1984b), Hansen (1992), and Cellinese (2002, 2003).

According to previous phylogenomic analyses, P. multisepala is closest to Phyllagathis setotheca H.L.Li from China (Zhou et al. 2022). However, the two species are quite distinct in leaf size (2.4–8 × 0.7–2.4 cm vs. 10–20 × 3–8 cm), number of flowers per inflorescence (1 or 2, rarely 3 vs. 3 to more than 20), number and shape of calyx lobes (4–8, linear vs. 4, long triangular) and length of pedicels (1–2 mm vs. 8–18 mm). In terms of morphology, P. multisepala closely resembles P. fruticosa and P. stenophylla. All three species are shrubs with druses, somewhat oblong-lanceolate, coriaceous, 3-veined leaf blade, few-flowered inflorescences, and narrow calyx lobes. Nevertheless, P. multisepala can be easily distinguished from the latter two species in the petals 28 × 9 mm, apically long acuminate (vs. 8.5–16 × 3.5–5 mm, acuminate, and 12 × 6 mm, short acuminate), calyx lobes 4–8 (vs. 4) and pedicels 1–2 mm at fruiting stage (vs. 10–15 mm). A comparison of the four species can be found in Suppl. material 1: table S1.

Perilimnastes setipetiola is resolved as sister to P. uniflora, and P. setipetiola-P. uniflora to P. banaensis (Zhou et al. 2022). Despite their close relationship, these species are morphologically quite different from one another. Perilimnastes uniflora is characterized by its small size (to 30 cm tall), the whole plant glabrous except for sparse minute brown glands when young, stems prostrate at middle and lower parts, leaf blade obovate to obovate-lanceolate, and solitary flower. Perilimnastes setipetiola and P. banaensis resemble each other in the shrubby habit, leaf size, somewhat elliptic leaf blade, and sessile or subsessile inflorescences with multiple flowers, however, the two species differ markedly in the indumentum of the stems and petioles (stems and petioles pubescent with stellate hairs when young, petioles hispid with stout, 2–4 mm long bristles vs. densely villous with appressed brown hyaline uniseriate hairs). According to Zhou et al. (2022), P. setipetiola, P. uniflora, and P. banaensis formed the sister clade of a Bornean lineage containing Phyllagathis elliptica Stapf and P. dispar (Cogn.) C.Hansen. The former three species are linked to the Bornean lineage by the presence of raphide crystals, somewhat elliptic leaf blade, and terminal and axillary umbels with very short or no peduncles in some of the species, however, they can be distinguished from the latter based on a combination of height, habit, indumentum, and anther morphology. In addition to the Bornean lineage, P. setipetiola shares similarities in habit, leaf size and shape with P. setotheca and P. ovalifolia H.L.Li. However, it differs from the latter species in terms of the indumentum of leaf petiole and the length of peduncles. Perilimnastes uniflora also resembles Phyllagathis guillauminii H.L.Li and P. rupicola, two species not sampled in previous phylogenetic studies, in crystal type and leaf shape, but differs in indumentum and the length of the pedicel at fruiting stage. A comparison of the species discussed above is provided in Suppl. material 1: table S2.

Phylogenetic data and morphological comparison justify the recognition of P. multisepala, P. setipetiola, P. uniflora, and P. banaensis as distinct species in Perilimnastes. The formal taxonomic treatment of other species in the Phyllagathis (raphides) clade will be dealt with in another study.

The four new species are geographically quite isolated from related species previously discussed (Suppl. material 1: tables S1, S2). Perilimnastes multisepala is located in central Vietnam (Fig. 1), whereas its related species, P. setotheca and P. stenophylla are documented in southernmost China and northern Vietnam, and P. fruticosa in the Malay Peninsula. Perilimnastes setipetiola is distributed in Đà Lạt, southern Vietnam and P. banaensis and P. uniflora are found in central Vietnam (Fig. 1). The three species are morphologically/phylogenetically related to P. elliptica, P. dispar, P. rupicola, P. setotheca, P. ovalifolia, and P. guillauminii. Phyllagathis elliptica, P. dispar, and P. rupicola are endemic species of Borneo, P. setotheca and P. ovalifolia are found in southernmost regions of China and northern Vietnam, while P. guillauminii has been documented in Bien Hoa, southern Vietnam. Members of the Phyllagathis (raphides) clade typically inhibit moist and shady environments in forests, such as damp slopes or rocky areas along or near streams and waterfalls. However, it is uncommon for multiple species of this clade to coexist in the same location. In this particular case, only P. banaensis and P. uniflora were observed together at an elevation of 1,360 m near the summit of Ba Na Hills in central Vietnam. Nevertheless, the two species prefer somewhat different microhabitats. Individuals of P. banaensis occupy damp slopes alongside other shrubs and lianas, whereas those of P. uniflora typically inhabit moist exposed rocks with fewer shrubs and lianas around.

We are grateful to Dr. David E. Boufford and the anonymous reviewer for their valuable comments on the manuscript.