Introduction

Dendrobium Sw., belonging to the tribe Malaxideae, subtribe Dendrobiinae, is the third largest orchid genus encompassing about 1600-1800 species distributed from Sri Lanka throughout tropical Asia and the Pacific region, north to Japan, east to Tahiti and south to New Zealand (^{Schuiteman & Adams 2014}, ^{Chase et al. 2015}, ^{Ormerod 2017}). At present, the number of Dendrobium species in Indonesia is around 680 species (Ormerod unpubl. data). In Sumatra, the genus is represented by approximately 140 species and future fieldwork would probably result in the discovery of more species either endemic or as new records from neighbouring countries and islands (^{Juswara et al. 2018}).

In the recent floristic survey conducted in the westernmost province of Indonesia by the second and third authors, an unknown Dendrobium species was collected in the province of Aceh, Sumatra. Upon detailed morphological examination and comparison to the relevant literature and digitized type specimens of Dendrobium from Indonesia and neighbouring countries, the species matches with D. bandii Cavestro, a poorly known species recently described.

A careful analysis of our recently collected specimen revealed that the description and line drawing provided by ^{Cavestro (2020}) are not entirely accurate: the diagnosis and some morphological characters recorded by the author (e.g. acute to obtuse leaf apex, oblong-triangular lateral sepals, broadly ovate midlobe of the labellum, column length, among others) are probably more variable than the protologue suggests, and some morphometric features were omitted in the original description (e.g. column foot measurement, claw measurement, stelidia shape and measurement and many more). Thus, to further clarify the identity of this taxon, we present here an amended description of D. bandii, a colour photograph to aid accurate identification, ecological notes and its provisional conservation status.

Materials and methods

The measurements and descriptions were based on freshly collected material deposited at Herbarium Bogoriense (BO). The general plant descriptive terminology follows ^{Beentje (2016}). Informal conservation status category was assessed by range size (B criterion), following IUCN Standards and Petitions Subcommittee (²⁰¹⁹) recommendations. The extent of occurrence (EOO) and area of occupancy (AOO) were estimated using GeoCAT (^{Bachman et al. 2011}).

Taxonomic treatment

Dendrobium bandii^{Cavestro, Orchidee (Hamburg) 6(120): 176, 2020}. TYPE: INDONESIA. North Sumatra: District of Aceh, elev. ca. 1300-1600 m, 18 February 2020, W. Cavestro and A. Marup s.n. (holotype, ANDA). Fig. 1.

A. Habit. B. Inflorescence. C. Flower (left, front view; right, profile view). D. Dorsal sepal. E. Petal. F. Lateral sepal. G. Labellum (left, top view; right, profile view). H. Pollinia. I. Anther cap. J. Pedicel with ovary, profile view of column, column foot and labellum. K. Ventral view of column and column foot.

Figure 1 Dendrobium bandii Cavestro. 

Epiphytic, pendent, herb. Roots elongate, ca. 1.5 mm long, glabrous. Stem slightly flexuous, 15-40 cm long by 0.3-1.2 cm in diameter, terete at the base, slightly flattened in ⅔ of the upper part, young stem rounded, green; internodes ca. 1.5-4 cm long. Leaves distichous, deciduous; sheaths tubular, clasping the entire internode, brown; leaf blades lanceolate-elliptic, 9.5 cm long by 3.0 cm wide, with 4 veins, chartaceous, green, glabrous, margin entire, apex subacuminate to acuminate. Inflorescence 2- or 3-flowered, arising from the older, leafless stems; peduncle 10-11 mm long, terete, glabrous. Flower 2.5 cm across, apricot or orange pink to yellow or greenish yellow with crimson spots on the labellum and the ventral side of the column foot. Pedicel and ovary 13 mm long, corrugated, glabrous, pale green, whitish near apex. Dorsal sepal 3-veined, incurved, nodding, ovate, 15 mm long by 8-9 mm wide, glabrous, covering the column, margin entire, apex obtuse. Lateral sepals 7-veined, spreading, broadly falcate, 15-16 mm long by 20-23 mm wide, glabrous, forming a mentum with the column foot 20-21 mm long, margin entire, apex acute, cucullate. Petals 1-veined, pointing forward, obovate, 15 mm long by 5-7 mm wide, glabrous, covering the column, margin entire, apex rounded. Lip 3.2 cm long by 1.8 cm wide; claw ligulate-oblong, subsigmoid in lateral view, basal 2-3 mm excavate and joined to column foot, free part ca. 7-8 mm long, in total ca. 10 mm long by 2-3 mm wide; blade weakly trilobed, broadly rhombic, 13-15 mm long by 12-14 mm wide, glabrous, margins slightly undulate to entire, fleshy, apex broadly, obtusely bilobed; callus oblong, shallowly canaliculate, base raised, obtuse, slightly retrorse, beginning midway on the claw and terminating on the basal quarter of the blade; mentum narrowly-conical, 2.0-2.1 cm long, curved, acute. Column stout, 3-4 mm long, with a crimson stripe on the underside; column foot 20-21 mm long; stelidia triangular, 1.0-1.5 mm long; pollinia 2, each pair can be divided into two parts, 1 mm long by 1.3 mm across, yellowish; anther-cap cucullate, 3 mm across, subhyaline. Capsule not seen.