Two new Orchidantha species ( Lowiaceae ) from Borneo

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INTRODUCTION
Lowiaceae (Zingiberales), with a single genus Orchidantha N.E.Br., is a small family of about 21 species restricted to Asia.A more detailed general introduction to Lowiaceae was given in Trần & Leong-Škorničková 2010.Recent work on Lowiaceae has uncovered several new taxa from continental Asia (Trần & Leong-Škorničková 2010, Leong-Škorničková 2014, Leong-Škorničková et al. 2014, Zou et al. 2017) as well as one new species from Borneo (Syauqina et al. 2016).Eight species (and one variety) of the family Lowiaceae are found north of the Isthmus of Kra throughout the Indochinese floristic region and into southernmost China.Five different species occur on the Malay Peninsula and eight species are currently known to be endemic in Borneo.
Orchidantha borneensis N.E.Br., the type species of the genus, was the very first Orchidantha described (Brown 1886).The Compagnie Continentale d'Horticulture, Ghent, Belgium, introduced a live plant from Borneo to Europe without precise information of the locality of origin.The type specimen made from this cultivated plant, however, is well-preserved and the description is sufficiently detailed to establish that O. borneensis is a small species with light-coloured free and spreading sepals and a dark purple labellum and petals.Unfortunately, Larsen (1998) confused the understanding of the morphology of O. borneensis when he included a photograph by Josef Bogner.This photograph is of a cultivated plant, originally collected in 1994 at Matang, Sarawak, Borneo, flowering at Munich Botanical Garden in 1997(acc. no. 94/1211).We studied pressed herbarium material of this plant (Bogner 2146, AAU (including four additional photographs), M).Due to the larger size of the flowers with white petals and a labellum with pale yellow apex, we have to conclude that this material does not match the type and original description of O. borneensis.Instead, Bogner's collection is very similar, if not conspecific, with the recently described O. ranchanensis Syauqina & Meekiong, also from Sarawak.
New collections from Matang at the eastern side of Kubah NP (where Bogner collected 94/1211 between the national park headquarters and the Red Bridge, Bogner pers.comm.), and elsewhere in Sarawak are needed to completely understand the morphological variation and distribution of O. ranchanensis as well as establish the likely origin of O. borneensis.
Seven species of Orchidantha were subsequently described from Borneo: Larsen (1993), Nagamasu & Sakai (1999), Pedersen (2001), Syauqina et al. (2016).Most of these are adequately described and illustrated, making identification of any new taxa uncomplicated and all are well localised.Two interesting Orchidantha species, first collected by ADP during fieldwork in Sarawak in 2003, are described and illustrated below as O. micrantha and O. megalantha, respectively.This brings the total number of Bornean species to ten with one species known from Brunei, four species each from Sabah and Sarawak and, as mentioned above, O. borneensis, unlocalised.The descriptions of the vegetative characters are based on li ving plants and dry herbarium specimens, measurements of all flower parts were made from herbarium material preserved in spirit.The style of description follows recent works of Leong-Škorničková cited above, with general plant descriptive terminology following Beentje (2016).Etymology.The epithet refers to the small flowers relative to other species of the genus.Conservation status -Orchidantha micrantha is reported from two populations each of several individuals a few hundred metres apart at the same general habitat within a protected area with no perceived threats.As the number of mature individuals is < 1 000, it may be considered 'Vulnerable' (VU) D1 (IUCN Standards and Petitions Subcommittee 2017).

Orchidantha micrantha
Notes -1.In Borneo, this species is most similar to O. borneensis due to its small habit, and similarity in size and colouring of the flower although the differences in flower structure as outlined in the diagnosis makes the two species unmistakeable.Further differences between the two species, based on  examination of the type specimen of O. borneensis which has two well-preserved flowers (Fig. 3) can be outlined as follows: Orchidantha micrantha has petals where the margin at apex is irregularly serrate, an ovate to elliptic labellum c. 23 × 10 mm with a prominent midrib throughout the entire length, and the margin to the stigma is irregularly denticulate whereas O. borneensis in comparison has petals with an entire margin, a linear c.21 × 3.5 mm labellum where the midrib is only prominent in the lower half, and the stigma margin laciniate.The recently described O. ranchanensis from Sarawak also has spreading sepals and is therefore easy to distinguish from O. micrantha.
2. In continental Asia, the morphologically most similar species would be O. stercorea H.Đ. Trần & Škorničk. (colour figure in Trần & Leong-Škorničková 2010) and O. laotica K.Larsen (colour figure in Zou et al. 2017).Both species are small and have flowers with a dark labellum in a claw-like arrangement of pale-coloured sepals.Neither of these species has an undulate labellum margin.In addition, O. laotica has lamellate yellow stripes at the base of the labellum, while the flowers of O. stercorea are larger than those of O. micrantha.-Fig.4, 5
Habitat & Ecology -Growing on a sandy hill c. 300 m from a limestone cliff.Flowering observed in the field in April and July.
Conservation status -Orchidantha megalantha is reported from one population on a sandy shallow hill with several individuals within a national park area with no perceived threats.As the number of mature individuals is < 1 000, it may be considered 'Vulnerable' (VU) D1 (IUCN Standards Petitions Subcommittee 2017).
Note -Orchidantha megalantha resembles O. holttumii K.Larsen (Fig. 6) by the height not exceeding 1.5 m and the presence of petiolate leaves in both young and adult individuals.The shape of the flower is also similar; the two lateral sepals overlapping below the labellum and the dorsal sepal arching over it, resulting in claw-like appearance of the flower.The flower of O. megalantha is, however, twice as big as that of O. holttumii, the sepals are bright yellow-green and stigma is purple (compared to pale greenish sepals and white stigma in O. holttumii).So far, all species of Orchidantha are known to be very restricted in their distribution (Sakai & Inoue 1999).The difference in the size and colouration of the flower is likely an adaptation to a specific pollinator, most likely a dung beetle, as previously reported for other species of Bornean Orchidantha (Sakai & Inoue 1999, Pedersen 2001).

Fig. 3
Fig. 3 Orchidantha borneensis N.E.Br.a. Flower; b. detail of stigma, stamens and petal (all of the holotype at K [K000292159] reproduced with permission of the Director and Board of Trustees, Royal Botanic Gardens, Kew).-Photos: Jana Leong-Škorničková.

Fig. 5
Fig. 5 Orchidantha megalantha Škorničk.& A.D.Poulsen.a. Petals, stamens and style with stigma (ventral view); b. petal with two stamens attached; c-e.detail of stigma in ventral, dorsal and lateral view (all: Poulsen et al. 2073, pickled material).-Drawing by Axel Dalberg Poulsen.c b d a e for research on Zingiberales in Sarawak for the first author in 2003; the Forest Department in Sarawak gave permission to conduct the research in 2014.His fieldwork was kindly supported by HRH Frederik, Crown Prince of Denmark.The research of the second author was supported by the National Parks Board, Singapore and by the Czech Science Foundation, GAČR (Grant No. P506/14/13541S).We should also like to thank the keepers of the herbaria of AAU, E, K, KEP, M, P, SAN, SAR and SING for letting us examine their collections and sending material on loan, staff at SBC and Forestry Research Centre, Mulu NP and Kubah NP in Sarawak for logistic and other help, and Muhd Ariffin Abdullah Kalat (BRUN) for letting us use his photographs of O. holttumii.At Munich Botanical Garden, we are grateful to its director, Susanne S. Renner for inviting the first author on a research visit, Josef Bogner for providing locality information of his collection and useful discussions, Till Hägele for checking accessions in the live collection database and Hajo Esser for providing digital images of herbarium specimens.Fig.3isreproduced with permission of the Director and Board of Trustees, Royal Botanic Gardens, Kew.