Sonerila longipedunculata sp. nov., a new species of Melastomataceae from the southern Western Ghats, India, with additional notes and lectotypification of Sonerila travancorica

A new species of Melastomataceae, Sonerila longipedunculata Resmi & Nampy sp. nov., is described from the southern Western Ghats, India. It is morphologically close to S. travancorica, but differs by the tuberous root stock, fleshy stems, ovate to cordate lamina, longer, angular peduncles, 3-ribbed hypanthium, ovate-elliptic petals, acute anthers, and 3-ribbed capsules. Detailed description, distribution map, and photographic images are provided. The morphological differences with relevant species are discussed. The status of the new species is provisionally assessed here as ‘critically endangered’ according to IUCN Red List Categories and Criteria. The name Sonerila travancorica is lectotypified and its identity is discussed. The status of Sonerila longipetiolata is discussed and is synonymised under S. travancorica.


Introduction
Sonerila Roxb. (Melastomataceae Juss., Sonerileae Triana) is a taxonomically complex genus with around 180 recognised taxa of terrestrial or low epiphytic herbs and sub-shrubs of shady habitats . The genus is distributed in the tropical Indo-Pacifi c region (Cellinese 1997), and is easily recognisable by its generally trimerous fl owers, mostly uniparous (scorpioid) cymes, and 3-locular, inferior ovary. Clarke (1879) recognised 43 species in the Flora of British India, ca 20 species of which are found within the present political boundaries of India. Currently, there are 62 species and two varieties reported in India, with the highest diversity (53 species and two varieties) in the Western Ghats, one of the major centres of diversity for the genus .
During botanical explorations in 2017-2019, as part of a taxonomic revision of Sonerila in India, an unknown species was collected in the southern Western Ghats, from the Kattukunnu of Banasura hills, within the South Wayanad forest division, Kerala. Following a careful review of herbarium specimens and taxonomic literature, we conclude that this species is new to science. The new species, Sonerila longipedunculata Resmi & Nampy sp. nov., is described and compared with Sonerila travancorica Bedd., a species described from the Travancore mountains by Beddome (1871). Further scrutiny revealed that, even though later researchers included the latter species in their studies (Triana 1871;Clarke 1879;Cogniaux 1891;Stapf 1892;Gamble 1919;Nair & Henry 1983;Mohanan & Henry 1994;Mohanan & Sivadasan 2002;Manickam et al. 2008), a type had not been designated, and hence we selected a lectotype according to the Shenzhen Code (Turland et al. 2018). We also came across the recently described species S. longipetiolata Josephine, Manickam, Murugan, Sundaresan & Jothi (Josephine et al. 2003), which was diff erentiated from S. travancorica based on size and shape of leaves, texture of indumentum, number of fl owers, and apex shape of calyx and corolla. However, a detailed examination of the protologue, type, and live material from the type locality revealed that the vegetative and fl oral features used to delimit S. longipetiolata are variable and overlap with the circumscription of S. travancorica. Therefore, we reduce S. longipetiolata to a synonym of S. travancorica.

Material and methods
All measurements and morphological character assessments were performed using living samples in the fi eld and cultivated specimens at Calicut University Botanical Garden. Specimens were processed following Vogel (1987) and Forman & Bridson (1989). The study was based on specifi c literature (Triana 1871;Beddome 1871;Clarke 1879;Cogniaux 1891;Stapf 1892;Gamble 1919;Nair & Henry 1983;Mohanan & Henry 1994;Mohanan & Sivadasan 2002;Josephine et al. 2003;Manickam et al. 2008). All available Indian specimens of Sonerila, including types, were examined in the following herbaria: BM, CAL, CALI, K, MH, TBGT, XCH. Acronyms of herbaria follow Index Herbariorum (Thiers, continuously updated). Specimen images were retrieved from JSTOR Global Plants (http://plants.jstor.org). Nomenclature was checked in Tropicos (http://www.tropicos.org) and the International Plant Names Index (http://www.ipni.org). For the description of taxa, the terminology follows Stearn (1992). Photographs were taken with an EZ4 HD stereo microscope with a 3.0 megapixel digital camera (Leica, Switzerland) and a Stemi 508 stereo microscope (Carl Zeiss, Germany) with an attached Axiocam 105 colour camera. Ecological and geographic distribution data were collected from herbarium labels; the distribution map was created using QGIS ver. 3.12.2 (QGIS 2020). Provisional conservation status assessments were based on guidelines published by the IUCN Standards and Petitions Subcommittee (2019).

Etymology
The epithet 'longipedunculataʼ refers to the characteristically long peduncle of the infl orescence of the new species.

Phenology
Sonerila longipedunculata sp. nov. was collected with fl owers and fruits from September to October.

Distribution and habitat
The new taxon is presently known only from a small area in the Kattukunnu of Banasura hills within the South Wayanad forest division (Fig. 1), where it has been growing under wet rocks on grassy slopes at an elevation of ca 1000 m. Although no detailed ecological studies have been undertaken, S. longipedunculata sp. nov. appears to be restricted to shaded rocky outcrops and is likely to occur in areas where a specifi c combination of light intensity and moisture prevails, such as vertical, mosscovered rocks or rock crevices, as is the case for many species of Sonerila. It is found in association with S. raghaviana Ratheesh, Sunil, Nandakumar & Shaju, species of grass (Poaceae Barnhart), Mitracarpus Zucc. (Rubiaceae Juss.), Selaginella P.Beauv. (Selaginellaceae Willk.) and several mosses.

Provisional conservation status
Sonerila longipedunculata sp. nov. is known from a single population in the type locality with about 60 mature individuals. The Area of Occupancy (AOO) is less than 10 km 2 . No anthropogenic threat was detected as the area falls under a protected forest. However, this area is prone to landslides due to heavy rain, which has occurred in previous years. The habitat has been aff ected by climate-induced draught after the unexpected fl oods in 2018 and 2019. We suggest the status of S. longipedunculata sp. nov. as Critically Endangered (CR) B1ab(ii) + B2ab(ii) according to IUCN (2019) criteria.

Notes
The new species is remarkable by the presence of a tuberous root stock (Fig. 2C-E), a feature seen in some of the South Indian caulescent species of Sonerila that is apparently absent in Sri Lankan    species (Lundin 1983), but also reported in species from the Malay Peninsula, Vietnam and Cambodia (Ridley 1912;Pham 2003;Cho et al. 2015;Van Dang et al. 2016). These tubers, with the arrival of the monsoon, produce new stem and tufts of roots. The species of Sonerila from India are mostly pedunculate (with terete or angular peduncles) and rarely sub-sessile. The longer peduncles (10-16 cm) and petioles (5-9 cm) further distinguish the new species, and these traits are not described in any other caulescent herbaceous species, other than the suff rutescent or woody species of Indian Sonerila. Sonerila longipedunculata sp. nov. has fl eshy and simple stems, which occasionally branch at distal nodes and become procumbent with roots arising from many points along the stem basally, when grown in the greenhouse. Sonerila longipedunculata sp. nov. is also similar to S. raghaviana Ratheesh, Sunil, Nandakumar & Shaju described by Narayanan et al. (2014) in the hair pattern and fl oral features, but diff ers from it by the plants being caulescent (vs acaulescent / scapigerous). A comparison of diagnostic characters between S. longipedunculata sp. nov. and S. travancorica is provided in Table 1.

Notes on phenology and habitat
Sonerila travancorica was collected with fl owers and fruits from January to April. This endemic species is found only in the Agasthyamala Biosphere reserve in the southern Western Ghats (Fig. 1). Sonerila travancorica occurs in shady terrestrial habitats, but occasionally is found on the base of tree trunks or rocks with a relatively thick mossy substratum. It grows along the margins of sholas and near streams, waterfalls or dam areas at elevations above 1200 m.

Provisional conservation status
This species is known from six locations in Agasthyamala Biosphere reserve in Kerala and Tamil Nadu. The estimated Extent of Occurrence (EOO) is ca 300 km² and Area of Occupancy (AOO) is 12 km². The authors surveyed three locations and found a total of 230 mature plants. Since these locations are inside a protected area, the risk of a decline due to anthropogenic activity is small. Based on the above data, the species is provisionally assessed here as Endangered (EN) B1ab(iii, iv, v), D (IUCN 2019).

Discussion
The genus Sonerila displays a wide morphological diversity and S. longipedunculata sp. nov. is recognised as a new species, thanks to extensive fi eld work across India designed to generate a modern, comprehensive taxonomic treatment of the genus. Two other taxa, S. travancorica and S. longipetiolata, were examined and re-evaluated in this study.
Sonerila travancorica is exceptionally variable in its vegetative and fl oral morphology, including the shape of lamina (ovate to elliptic), base of lamina (equal or unequal and narrow to sub-rounded to cordate), length of petiole (2-7 cm long), colour and apex of the petals (dark pink to pale pink and mucronate to emarginate at apex), and number of fl owers (4-16).
Sonerila longipetiolata was described by Josephine et al. (2003) from Muthukuzhivayal in Tirunelveli district of Tamil Nadu. During our botanical explorations in diff erent parts of the southern Western Ghats, we studied a large number of specimens of this species from diff erent areas of Kodayar, including the type locality (Kakkachi, Muthukuzhivayal and Kodayar Dam areas). A critical examination of protologues, type specimens and living material showed that the characters used to delimit S. longipetiolata fall within the range of S. travancorica, hence S. longipetiolata is reduced to a synonym of S. travancorica.
Sonerila travancorica was originally described by Beddome (1871) who cited the type locality as "Travancore mountains (Attraymallay), 3500-5000 feet" but did not specify a holotype. The main set of Beddome's collections (including types) is known to be at BM, K and CAL (Stafl eu & Cowan 1976). We   have found one specimen at K (K000867664) and two specimens at BM mounted on the same sheet with two barcodes numbers (BM000793170 and BM000944457), which bears a fi eld note "Attraymallay ghat/ Travancore 3023 & 3022" in Beddome's handwriting, and two labels "Herb. Col. R.H. Beddome-Received 1885" and "Type specimen". The sheet K000867664 bears an annotation "115-from Major Beddome, Travancore 4000ft, 4/1870". We have selected the specimen BM000944457 as the lectotype because it explicitly mentions the type locality and therefore, it represents the best choice among the available material.