﻿Four new species of Perilimnastes (Sonerileae, Melastomataceae) from Vietnam

﻿Abstract 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 Perilimnastesmultisepala, P.setipetiola, P.uniflora, and P.banaensis. Perilimnastesmultisepala is phylogenetically closest to Phyllagathissetotheca, 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. Perilimnastessetipetiola, P.uniflora, and P.banaensis are phylogenetically most closely related. Perilimnastesuniflora is characterized by its prostrate habit, small size, glabrous, obovate to obovate-lanceolate leaf blade, and solitary flower. Perilimnastessetipetiola 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.

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 2002Cellinese , 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

Morphological comparison
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 (2002Cellinese ( , 2003)).
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.

Geographical distribution
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.Diagnosis.Resembles P. fruticosa and P. stenophylla in the habitat preference, habit, leaf and inflorescence morphology but differs from these species in the petals 28 × 9 mm, apex 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 only 1-2 mm at fruiting stage (vs.10-15 mm).
Phenology.Flowers, young fruits and old fruits in November.

Perilimnastes setipetiola
Phenology.Flowers and old fruits in November.
Etymology.The specific epithet is based on the stout long bristles on the petiole of this species.

Perilimnastes uniflora
Phenology.Flowers in June and produces old fruits in November.
Etymology.The specific epithet is based on the solitary flowers of this species.Distribution.Perilimnastes uniflora is currently only known from Ba Na Hills, Hòa Ninh, Đà Nẵng, Vietnam (Fig. 1).It occurs on damp rocks along streams in forests, at 1,360 m elevation.Diagnosis.Resembles P. ovalifolia and P. setipetiola in having raphide crystals, hyaline hairs, somewhat elliptic leaf blade, and umbels with very short or no peduncle, but differs in the stems and petioles densely villous with brown hyaline uniseriate hairs (vs.stems densely retrorse hirsute, glabrescent, and petioles densely hirsute to setose in the former species, and stems pubescent with brownish-yellow stellate hairs and rarely also hyaline hairs, petioles with brownish-yellow stellate hairs when young and hispid with long bristles in the latter).

Perilimnastes banaensis
Description.Shrubs to 60 cm tall, with raphides in all parts.Stems branched, prostrate at lower parts; branchlets obtusely 4-sided and densely villous with appressed, brown hyaline uniseriate hairs composed of much elongated cells and tipped with a brown glandular cell; older branches near terete and glabrescent; leafy distally and leafless proximally.Leaves opposite, equal to unequal in a pair; petiole 1.5-4.6 cm long, densely villous with appressed, brown hyaline hairs; leaf blade elliptic, 5.5-13 × 2.5-6.5 cm, thick papery, with minute brown glands when young on both surfaces, abaxially sparsely pubescent with appressed brown hyaline hairs, densely so along the veins, 3 or 5-veined, dark green adax-  Phenology.Old fruits in November.
Etymology.The specific epithet is based on Ba Na hills, the type locality of this species.

Figure 4 .
Figure 4. Perilimnastes multisepala A top view of a flower B longitudinal section of a flower showing the isomorphic stamens C top view of a young capsule D lateral view of a young capsule E top view of an old capsule F longitudinal section of an old capsule showing enlarged ovary crown and morphology of the placental column and placentas.Scale bars: 5 mm (B); 3 mm (F).All from Jin-hong Dai and Ying Liu 821 (A, PE, SYS).

Figure 6 .
Figure 6.Perilimnastes setipetiola A habit B adaxial (top) and abaxial (bottom) leaf surfaces C a flowering branch D a branch showing hispid petioles and terminal and axillary infructescences E top view of a flower F longitudinal section of a flower showing the isomorphic stamens G longitudinal section of an old capsule showing enlarged ovary crown and morphology of the placental column and placentas.Scale bars: 5 mm (E, F); 3 mm (G).All from Jin-hong Dai and Ying Liu 836 (A, PE, SYS).

Figure 8 .
Figure 8. Perilimnastes uniflora A habit B a flowering individual C close-up of a branchlet D adaxial (left) and abaxial (right) leaf surfaces E a flowering branch F close-up of an inflorescence showing a solitary flower G top view of a flower H longitudinal section of a flower showing the isomorphic stamens I longitudinal section of an old capsule showing enlarged ovary crown and morphology of the placental column and placentas.Scale bars: 5 mm (D, G, H); 2 mm (I).All from Jin-hong Dai and Ying Liu 814 (A, PE, SYS).

Figure 10 .
Figure 10.Perilimnastes banaensis A habit B a branch with old capsules C close-up of a branchlet D adaxial (left) and abaxial (right) leaf surfaces E a sessile infructescence F longitudinal section of an old capsule showing enlarged ovary crown and morphology of the placental column and placentas.Scale bars: 2 mm (F).All from Jin-hong Dai and Ying Liu 813 (A, PE, SYS).