Introduction

Described by Blume in 1825, the genus Dendrochilum belonging to the subfamily Epidendroideae, is a largely Malesian orchid genus encompassing over 280 species (^{Sulistyo et al. 2015}, ^{Ormerod 2017}). With approximately 120 known species, the Philippines are considered as a center of diversity for this genus (^{Cootes 2011}, ^{Pelser et al. 2011}). Given that most Dendrochilum species are restricted to cool, humid, and often exposed conditions in montane forests with an unusually high share of narrow endemism (^{Pedersen 2007}a), it is believed that there are still a number species awaiting discovery and description, especially in Mindanao, as this island is composed of a number of high mountains which are relatively unexplored botanically (e.g.^{Cootes 2017}, ^{Naive et al. 2017}).

Fresh materials of an interesting but unknown Dendrochilum plant identified as a member of the section Platyclinis because of the synanthous inflorescences, entire rostellum, presence of stelidia and an apical wing on the column, was collected during the first author’s excursion in the province of Bukidnon on the island of Mindanao in the Philippines in June 2017. After meticulous examination of its morphology and comparison with protologues and digitized type specimens of Dendrochilum sect. Platyclinis species from the Philippines (^{JSTOR 2018}) and neighbouring countries, we found the material matches with Dendrochilum warrenii H.A.^{Pedersen & Gravend. (2004}: 358). This species was first exhibited at the European Orchid Conference in London by Blair Sibun (Pedersen et al. 2004). It was then described by Pedersen and Gravendeel in 2004 based on a specimen in cultivation provided by Richard C. Warren (after whom the species was named), with unknown provenance. Based on moleclar phylogenetic analyses, these authors hypothesized that the species could be originating from the Philippines and/or Sulawesi (Pedersen et al. 2004, ^{Sulistyo et al. 2015}). The present publication reports the first collection of D. warrenii from the wild, confirming a Philippine origin. An extended species description based on this new collection in the field incorporating all current knowledge is provided together with color photographs to aid future identifications.

Materials and methods

Fresh plant material was collected during a botanical excursion in June 2017 in the Bukidnon province of the island of Mindanao in the Philippines. A spirit collection was deposited in the University of Santo Tomas Herbarium (USTH). Our descriptions of vegetative and reproductive characters are based on living plants and the spirit collection. The species description follows the style of ^{Pedersen (2011}) using general plant terminology of ^{Beentje (2016}). Below, we provide a detailed description and colored photographs as well as notes on the distribution, phenology, and ecology in the wild.

Taxonomic treatment

Dendrochilum warrenii H.A.^{Pedersen & Gravend., Blumea 49: 358-359. 2004}.

TYPE: Warren EQ 3066 (holotypus C), sine loco et coll./cult. Richard C. Warren anno 2003. Fig. 1.

Small, tufted, epiphytic herb. Roots arising from the rhizome, 1.0-1.5 mm in diameter, unbranched. Pseudobulbs clustered on a very short rhizome, fusiform, 1.0-2.1 cm long by 0.4-0.5 cm in diameter, unifoliate, covered with 1-4 tubular, attenuate to acuminate, papery cataphylls which soon disintegrate into persistent fibres. Leaf petiolate; petiole up to 1 cm long, distinctly canaliculate; lamina dorsiventrally complanate, coriaceous, narrowly linear, 10.0-10.2 cm long by 0.1-0.2 cm wide, with prominent midrib, margin entire, apex subacute. Inflorescence synanthous, racemose; peduncle straight to arching, up to 10.5 cm long, terete, very slender; rachis nodding to pendent with distichously alternating flowers, dense, up to 12-flowered with internodes of ca. 2 mm, slightly furrowed, 3.0-3.5 cm long, basally with 3-4 non-floriferous bracts. Flowers white to greenish white; floral bracts persistent, glumaceous, lanceolate to narrowly lanceolate, 5-6 mm long by 2.0-2.1 mm wide, papery, striate, many veined, margin entire, apex acuminate. Dorsal sepal 3-veined, linear, 6.0-6.1 mm long by 1 mm wide, incurved, margin entire, apex acute to attenuate. Lateral sepals 3-veined, linear, 6.5-6.6 mm long by 2.7-3.0 mm wide, glabrous on both sides, margin entire, apex acuminate. Petals 3-veined, narrowly lanceolate, 4.4-4.5 mm long by 0.8-0.9 mm wide, glabrous on both sides, finely erose, apex subacute. Labellum 3-veined, sessile, lanceolate, 2.0-2.2 mm long by 1.0-1.1 mm wide, glabrous on both sides, margin finely erose, apex acute. Column short, subclavate, slightly incurved, 1.0-1.1 mm long, glabrous, distally prolonged into a bidentate wing exceeding the anther; stelidia inconspicuous, two, erect, margin entire, apex obtuse. Pollinia four, subpyriform. Rostellum flat, triangular. Ovary (including pedicel) semiterete, ca. 2.2 mm long, glabrous. Capsule not seen.

Distribution: The Philippines, Mindanao, province of Bukidnon.

Ecology: The species grows as an epiphyte at elevations approximately between 1,000 to 1,200 m asl among mosses on the trunks and branches of trees under shaded to slightly lit conditions in montane broad leaf forest.

Phenology: Observed flowering in the wild in the months of June and July.

Conservation status: Following ^{IUCN (2017)}, we propose this species to be treated as ‘Data Deficient’ (DD). Further field surveys are needed, as there is insufficient information to assess the status of this species with only limited distributional data and no information on population size, trends or threats to the species in the wild.

Specimen examined: PHILIPPINES. Mindanao: Bukidnon, elevation 1,200 m asl, 25 June 2017, M.A.K. Naive 101 (USTH, spirit material) - Full locality data are withheld to prevent potential exploitation of wild populations for commercial purposes; Warren EQ 3066 (holotypus C), sine loco et coll./cult. Richard C. Warren anno 2003.

Following the publication of protologues based on cultivated material since 2000, D. warrenii is the sixth species of Dendrochilum located in the wild. Earlier on, wild plants of D. coccineum H.A.^{Pedersen & Gravend. (Pedersen et al. 2004}), D. croceum H.A.Pedersen (^{Pedersen 2005}), D. quinquecallosum H.A.Pedersen (^{Pedersen 2007b}), D. undulatum H.A.Pedersen (Pedersen 2007b) and D. hampelii^{Sulistyo, Gravend., R.Boos & Cootes (Sulistyo et al. 2015}) were discovered in the field after having been traded for several years under commercial names such as ‘Sherborne Star’ (D. warrenii) and ‘Big Pink’ (D. hampelii) before their formal taxonomic descriptions were published. Following recommendations by Pedersen (2011) and Sulistyo et al. (2015), we rechecked The International Orchid Register (accessed on 16 September 2018) to verify whether any new artificial hybrids had been described but the latest addition for Dendrochilum was from 2000. Finding this species in the wild in a remote and pristine montane rainforest, together with the congruent molecular phylogenetic positions provided by biparentally inherited nuclear genes and maternally inherited plastid genes and distinct single peaks in all chromatograms (Pedersen et al. 2004, Sulistyo et al. 2015, Pedersen et al. in prep.) convinces us that D. warrenii is not of human assisted hybrid origin.

Figure 1 In situ photograph of Dendrochilum warrenii H.A.Pedersen & Gravend. showing its habit and flowers (inset). Photos made by M.A.K. Naive in the field in the Philippines.