﻿Bulbophyllumromklaoense (Orchidaceae), a new species from Thailand

﻿Abstract Bulbophyllumromklaoense (B.sect.Lemniscata) from northern Thailand is described and illustrated as a species new to science. It is most similar to B.muscarirubrum and B.triste, but differs by having inflorescences with only 4–6 reddish-brown flowers, falcate-subovate lateral sepals that are connate only in the upper half along the interior margins, petals with erose to fimbriate margins and a lip with long cilia in the distal half on the lower surface. A comparison with other similar species in the section, as well as notes on ecology, phenology, conservation assessment and a key to B.sect.Lemniscata in Thailand are also provided.


Introduction
Bulbophyllum Thouars is the largest genus in Orchidaceae, encompassing approximately 2170 accepted species (POWO 2023).This mega-genus is characterised by a rhizome with 1-or 2-leaved pseudobulbs, an inflorescence that arises from the base of the pseudobulb, a mostly moveable lip attached to a distinct column foot and usually (2-)4 often unequal waxy pollinia (Vermeulen et al. 2014a).The genus is widely distributed in tropical to subtropical regions throughout America, Africa, Asia and Australia (Dressler 1993;Vermeulen et al. 2014a).In Thailand, about 163 species have been recorded, including five new species and a new record published in the last decade (Seidenfaden 1979(Seidenfaden , 1995;;Chayamarit et al. 2014;Vermeulen et al. 2014bVermeulen et al. , 2017Vermeulen et al. , 2021;;Pingyot et al. 2019).
Ban Romklao Botanic Garden (BRBG), a satellite garden of Queen Sirikit Botanic Garden in Chiang Mai (QSBG), was established in 1999 in Ban Romklao, Chat Trakan District, Phitsanulok Province, under the royal initiative.The garden covers an area of approximately 222 hectares, situated at an elevation of between 750 and 1300 m. highest sandstone mountain (2100 m a.s.l.) is found.In 2007, Mr. Nawin Inthakul, a living collection keeper, discovered a small Bulbophyllum on an oak tree in the lower montane forest of BRBG during his routine native plant check listing and collected some material.The living specimens were brought to the nearby BRBG orchid nursery, where they bloomed in February 2008.Subsequently, specimens were sent to the authors of the present paper for identification.However, they could not match them with any known species and, therefore, interpreted them as the representative of a new species, which is described in this article.

Material and methods
The unknown Bulbophyllum specimens were collected in BRBG in Phitsanulok Province and both living and alcohol material were sent to QSBG in Chiang Mai.Alcohol material was preserved in 70% ethanol.The living plants were transplanted into an orchid ex-situ collection at the QSBG nursery, while the alcohol specimen was deposited in the Herbarium (QBG).For morphological examinations, dissections and measurements, a stereomicroscope was employed.The key to species of B. sect.Lemniscata in Thailand was drafted, based on the keys to B. sect.Tripudianthes and B. sect.Pleiophyllus in Seidenfaden (1979).Type.Thailand.Phitsanulok Province, Chat Trakan District, Ban Romklao Botanic Garden, ca.1300 m a.s.l., 15 February 2008, Inthakul N887-50 (holotype QBG!, isotypes QBG! (2 sheets)).
Habitat and phenology.Epiphytic on oak trees (Lithocarpus spp.) in open evergreen broad-leaved lower montane forest, ca.1300 m a.s.l.Fl.January-February.
Distribution.Northern Thailand.This new species is currently known only from the type locality, which is located less than 7 km from the Lao PDR border.It is possible that this species occurs in Lao PDR or in other areas around the Phu Soi Dao Plateau (Fig. 3).
Etymology.Named after its type locality at Ban Romklao (Romklao Village).Conservation status proposed.This new species is known only from the type locality, situated in the protected area of BRBG.However, the Extent of Occurrence (EOO) and the Area of Occupancy (AOO) are less than 100 km 2 and 10 km 2 , respectively.The number of mature individuals is less than 50.Moreover, its habitat is frequently threatened by forest fires and climatic changes, such as warmer and drier conditions that increase drought and extend the fire season.These factors have led to significant habitat destruction.Thus, this species is preliminarily assessed as Critically Endangered (CR; B1+B2ab(iii,v)+C2a(i)), based on current information and according to the IUCN Red List Categories and Criteria (IUCN 2022).
Note.Vermeulen et al. (2014a) redefined Bulbophyllum sect.Lemniscata Pfitz.by including B. sect.Tripudianthes Seidenf.(except B. blepharistes Rchb.f.) and B. sect.Pleiophyllus J.J. Sm.Bulbophyllum romklaoense also belongs to section Lemniscata, characterised by its two-leaved pseudobulbs, deciduous leaves, elongate racemes, 4 pollinia and connate lateral sepals.This section contains ca.37 species, mainly distributed in South and South-East Asia (Vermeulen et al. 2014a(Vermeulen et al. , 2021;;Averyanov et al. 2019;Zhou et al. 2022;Nguyen et al. 2023).Currently, 26 species in this section are known from Thailand.According to Seidenfaden's key (1979), B. romklaoense would belong to section Pleiophyllus by its 2-leaved pseudobulb and lateral sepals that are not much longer than the dorsal sepal.Vermeulen et al. (2014b) synonymised Bulbophyllum tripaleum Seidenf.under B. dhaninivatii Seidenf.because the only differentiating character is the  presence of palea on the sepal apices, but this character is considered to be variable.We also observed this variability in a population of B. dhaninivatii at Phu Luang in Loei Province (north-eastern Thailand).Therefore, B. tripaleum is here treated as a synonym of B. dhaninivatii and is excluded from the key.

Figure 1 .
Figure 1.Bulbophyllum romklaoense Pingyot & Thawara A habit B pseudobulb with inflorescence arising from the base C flower, front view D flower, side view (right petal and right lateral sepal removed) E floral bract F dorsal sepal G lateral sepals (flattened & indumentum removed) H petals J column, top part K lip L anther cap (from Inthakul N887-50).Drawn by T. Pingyot.

Figure 2 .
Figure 2. Bulbophyllum romklaoense Pingyot & Thawara in vivo A habit (vegetative stage) B habit (flowering stage) C pseudobulb with inflorescence arising from the base D flower, front view E flowers, side view F lateral sepals.Photographed by P. Suksathan.

Figure 3 .
Figure 3.The distribution of Bulbophyllum romklaoense Pingyot & Thawara.The inset figure shows the position of this species on the complete map of Thailand.