Calamus siamensis Becc.

Moderate-sized densely clustering rattan climbing to 20 m. Stems without sheaths 0.9–2 cm diam., with sheaths 1.2–3 cm diam., internodes 15–45 cm long. Leaves ecirrate; sheaths greenish, often with scattered caducous grey-brown indumentum, densely armed with narrow triangular dark brown spines with pale green to yellowish swollen bases, the longest to 45 mm long, interspersed with much smaller spines to 5 mm long, the spines generally scattered, sometimes partly grouped, margins at the base of the spine tending to be swept downwards; ocrea inconspicuous, unarmed; knee conspicuous, armed as the sheath or unarmed; ocrea inconspicuous; flagellum to 2 m or more long; petiole 7–22 cm long, often shorter on sheaths subtending inflorescences; rachis arcuate, to 1.2 m long, bearing scattered straight spines to 2 cm on abaxial surface; leaflets up to 50 on each side of the rachis, regularly arranged or irregular and partly grouped, but leaflets held ± in one plane, the longest 11–33 x 1–2 cm, 1–3 veins bristly on the upper surface, abaxially with few bristles, the margins bristly. Inflorescences to 2.5 m long, including the terminal flagellum, male and female superficially similar, the male branched to 3 orders, the female to 2 orders, with up to 7 well spaced partial inflorescences; male rachillae 0.3–0.4 x 0.1 cm; female rachillae 3 –7.5 x 0.2 cm. Mature fruit globose, c. 0.8 cm diam., briefly beaked, and with c. 15 vertical rows of whitish scales, drying yellowish brown, with darker margins. Seed c. 0.5 cm diam.; endosperm homogeneous.