Lasianthus ranongensis (Rubiaceae), a new species from Andaman tropical rainforest Thailand

We describe Lasianthus ranongensis Sinbumr. & Napiroon as a new species in the genus Lasianthus. The new taxon is intensively discussed through taxonomic affinities and information on its habitat, distribution and conservation status is provided. Moreover, line drawings and stereo microscope images of important fertile organs are demonstrated. The new species is morphologically similar to L. stipularis but differs in its having flattened branches (vs. terete), leaf blade elliptic-oblong shape of 15.0–20.0 × 4.0–6.0 cm (vs. oblanceolate-oblong 12.0–16.0 × 3.0–5.5 cm), 9–12 pairs of veins (vs. 9–10 pairs), stipule 5–7 mm long, half covering cymes (vs. 10–12.5 mm long, entirely covering cymes), four or five bracts narrowly lanceolate, 2.5–3.0 mm long (vs. bracts numerous, broadly triangular, 10–15 mm), flowers with cupular calyx (vs. with campanulate calyx), corolla villous on internal surface, and six or seven lobed (vs. pubescent on internal surface and four lobed) and drupes with five pyrenes (vs. with four pyrenes). It is also similar to L. pseudo-stipularis, but from which it is obviously distinguished by its stipule half covers cymes, secondary veins have 9–12 pairs of secondary veins, cupular calyx shape, six or seven lobed corolla, and drupe with five pyrenes, whereas L. pseudo-stipularis has stipule entirely covering cymes, 7–8 pairs of secondary veins, obconic calyx, four lobed corolla, and drupe with four pyrenes.


INTRODUCTION
The genus Lasianthus Jack (Rubiaceae) includes about 180 species of which a majority of 160 species occur in Asian tropical rainforests (Zhu, Roos & Ridsdale, 2012). In the Southeast Asia, there are more than 142 species which have been treated separately for the different parts of the country (Ridley, 1923;Craib, 1934;Bakhuizen van den, 1965;Zhu, 1998;Zhu, 2001;Naiki et al., 2015). Advances in Lasianthus systematics have led to new discoveries, resulting in progress over the last twenty years following the establishment of the tribe Lasiantheae by Bremer & Manen (2000). Such publications have particularly improved our understanding of species distribution and diversity patterns at regional scales. For example, there is a continuous discovery of four new species and nine new recorded in Cambodia (Naiki et al., 2015;Naiki et al., 2017) since the last reports by Pitard (1924). The Malesian region, which includes Malaysia, Indonesia, Brunei, the Philippines, Papua New Guinea, Singapore and the Solomon Islands, 131 species with five subspecies and six varieties were recognized (Zhu, Roos & Ridsdale, 2012). In Thailand, Napiroon et al. (2020) have updated the list and enumerated 68 species based on herbarium specimens and results of their intensive field survey in the natural forests. Based on the synopsis and new species report of the Thai Lasianthus species, the genus is divided into two majors groups characterized by shape of cymes: sessile ordominantly pedunculated (Napiroon et al., 2018a;Napiroon et al., 2018b;Napiroon et al., 2018c;Napiroon et al., 2020). Also, presence and absence of bracts and bracteoles are useful characters for classification in Lasianthus. This diagnostic significance of peduncles and bracts were emphasized by Hooker (1880), but variation in length of the peduncles sometimes reduces its diagnostic importance. The flowers of Lasianthus are fragile and often lack in herbarium specimens thought it is still necessary for identification. Instead, Lasianthus could be identified by vegetative characters, such as the shape, size and indumentum on branches, leaf shape, stipules and the calyx (Naiki et al., 2015). Here, we describe a new species from the Andaman tropical rainforest of Thailand by using both completed fertile and vegetative organs collected from our field surveys.
We compared the sample with closely related species, including L. stipularis and L. pseudo-stipularis, using both completed fertile and vegetative organs. The apparent difference in morphological characters supports its recognition as a new species, which is here described.

Field surveys and ethics statement
Fieldwork by the Protected Area Regional Office 4, Department of National Parks Wildlife and Plant Conservation was conducted in the Andaman tropical rainforest in Ranong province, located at the West part of southern Thailand in May 2021. They collected an unknown Lasianthus species in flowering season from the natural condition. All samples were deposited at the BKF, Department of National Parks Wildlife and Plant conservation for the Flora of Thailand project. The herbarium abbreviations follow the Index Herbarium (Thiers, 2020). Our field studies did not involve any endangered or protected species. Since the species are currently undescribed, they are not currently included in the Threatened Plants of Thailand (Chamchumroon et al., 2017). No specific permits were required for the present study.

Morphological observation and conservation assessment
We use an exclamation mark (!) to indicate that a type specimen has been seen. Type specimens are cited partly based on online photographs from the herbaria and they are marked as "image!". Barcodes are given for type specimens together with the relevant literature (Zhu, 1998(Zhu, , 2001(Zhu, , 2002Zhu, Roos & Ridsdale, 2012). We used the morphological Lasianthus species concepts (Zhu, Roos & Ridsdale, 2012;Napiroon et al., 2020) to analyze and compare taxa, placing emphasis on reproductive and vegetative organs such as leaf characters, stipules characters, calyx shape, calyx size, indumentum, corolla characters, the number and morphology of the bracts and the number of pyrenes per drupe. Materials were examined using a stereo microscope (Olympus SZX16, Japan). Terminology and measurements, followed Beentje (2010) and references therein. Conservation assessments for new species follow IUCN Red List categories and criteria (IUCN, 2012;IUCN, 2019).
The electronic version of this article in Portable Document Format (PDF) will represent a published work according to the International Code of Nomenclature for algae, fungi, and plants (ICN), and hence the new names contained in the electronic version are effectively published under that Code from the electronic edition alone. In addition, new names contained in this work which have been issued with identifiers by IPNI will eventually be made available to the Global Names Index. The IPNI LSIDs can be resolved and the associated information viewed through any standard web browser by appending the LSID contained in this publication to the prefix "http://ipni.org/". The online version of this work is archived and available from the following digital repositories: PeerJ, PubMed Central SCIE, and CLOCKSS. Diagnosis:-Lasianthus ranongensis is morphologically similar to Lasianthus stipularis Blume, but differs in its having flattened branches (vs. terete branches), elliptic-oblong lamina 15.0-20.0 × 4.0-6.0 cm (vs. oblanceolate-oblong 12.0-16.0 × 3.0-5.5 cm), 9-12 pairs of secondary veins (vs. 9-10 pairs), glabrous young branches (vs. puberulous), stipules half covering cymes (vs. entirely covering cymes), bracts 4-5, 2.5-3.0 mm long (vs. bracts numerous, 10-15 mm long), glabrous cupular calyx, (vs. hirsute and campanulate), and 6-7 lobed corolla which inside is villous (vs. four-lobed and pubescent inside). In addition, it is similar to L. pseudo-stipularis Amshoff ex Bakh.f. but differs by having cupular calyx (vs. obconic), six or seven-lobed corolla (vs. 4-lobed).
Phenology:-Flowering and fruiting in May to June.
Etymology:-The specific epithet refers to its occurrence in the Andaman tropical rainforest, Ranong Province, the West part of southern Thailand.

DISCUSSION
Lasianthus ranongensis is a unique species but might be confused with L. stipularis, which is also found in peninsular Thailand, in having its similar habit and blue colored fruit. However, Lasianthus ranongensis is easily set aside from L. stipularis by the outstanding characteristics listed in the above diagnosis. In addition, this species is also similar to L. pseudo-stipularis. Both have large stipules but L. ranongensis presents a stipule with half covering cymes, leaves with 9-12 pairs of lateral veins, and cupular calyx. In contrast, Lasianthus pseudo-stipularis has a stipule that entirely covering cymes, leaves with

CONCLUSIONS
This study confirmed that Lasianthus ranongensis has morphological evidence as a new species that clearly distinguished from its resemble species. L. stipularis and L. pseudostipularis in both fertile and vegetative characters. These reports are useful for Flora of Thailand project to group of Lasianthus.