Accepted name: Dendrochilum geesinkii J.J.Wood in J.J.Wood & P.J.Cribb, Check-list Orchids Borneo: 175 (1994).
Within Kalimantan this species has been collected at Apo Kayan on the base of Mount Tapa Sia between Long Bawan and the Panado hill forest.
Within Sarawak this species has been collected in the Limbang District on the route to Batu Lawi.
The habitat has been described as hill forest on sandstone and mixed hill dipterocarp forest along a ridge top (Wood 2001).
The pseudobulbs cluster together on a rhizome that can grow to 6cm long; the pseudobulbs are spaced 0.5-0.6cm apart. The pseudobulbs are shaped cylindrical or narrowly oblong and measure 6.0-9.0cm long and 0.6-1.0cm in diameter. The pseudobulbs are covered by 3 cataphylls while they are growing. The cataphylls disintegrate into fibres as the pseudobulbs mature. The leaves are petiolate; the petiole measures 1.5-2.5cm long. The leaf blades are shaped oblong-elliptic, ligulate and have obtuse and mucronate to subacute apices. The leaf blades measure 11.5-22.0cm long and 1.4-2.2cm wide. The leaf blades are coriaceous and have 7 distinct nerves along their length.
The inflorescence is synanthous and appears when the leaves have almost fully expanded. The peduncle is erect to gently curved and measures 13-17cm long. The rachis is arching and measures 20-23cm long. The rachis is quadrangular in cross-section. The flowers alternate distichously and are spaced 1.8-2.0mm apart. There is one non floriferous bract at the base of the rachis.
The flowers are a pale green colour (Wood 2001). The dorsal sepal is shaped narrowly triangular and has an acuminate apex. The dorsal sepal measures 6.0mm long and 1.0mm wide. The dorsal sepal is 3-veined and has an entire margin. The lateral sepals are shaped narrowly-elliptic, subfalcate and have acute apices. The lateral sepals measure 5.5mm long and 1.0mm wide. The lateral sepals are 3-veined and have entire margins. The petals are shaped linear to narrowly elliptic, subfalcate and have acute apices. The petals measure 5.0mm long and 0.8mm wide. The petals are 3-veined and have minutely erose margins. The labellum is 3-nerved and obscurely 3-lobed. The labellum measures 3.8-4.0mm long and 2.0mm wide. The side lobes are auriculate and tooth like. The mid-lobe is papillose, shaped oblong-elliptic and has an obtuse apex. The margins of the mid-lobe are irregular. There are three keels than terminate half way along the mid-lobe. The keels are joined at the base of the labellum by a transverse ridge. The third keel is an elevated median nerve that joins the keels basally to form an M shape. The column is slightly incurved and measures 2.0mm long. The column foot is prominent. The apical hood is elongated, shaped oblong and has an obscurely tri-lobed apex. The stelidia grow upwards from the middle of the column and exceed the column apex. The stelidia are shaped narrowly triangular and have obtuse to acute apices.
Flowering plants have been collected during July and August.
Jeffrey Wood wrote that this species is related to Dendrochilum crassifolium but differs by its longer pseudobulbs, slightly smaller flowers, auriculate side lobes and stelidia that exceed the column apex (Wood 2001).
The epithet refers to the late Rob Geesink of the National Herbarium in the Netherlands (Wood 1997).
World Checklist of Selected Plant Families. 23 July 2009. The Board of Trustees of the Royal Botanic Gardens, Kew. Published on the Internet; http://www.kew.org/wcsp/ accessed 23 July 2009.