Calamus flagellum is an Asian species of tropical forest rattan liana in the family Arecaceae, with a native range from Assam to southern China and Indo-China. Its name in Vietnamese is mây song, while the Lepcha of Sikkim call it rim.[1]
Calamus flagellum is a strong climber with stems in clusters forming The individual rattan stems form from a leafsheath up to 45 mm in diameter. Leaves are described as "ecirrate" (without a cirrus: extension of the rattan leaf tip armed with grappling hooks), produced from leafsheaths 6 - 7 m long. Petioles are about 10 mm in diameter, armed with whorls of 10 - 30 mm spines; the leaflets are equidistant, broadly ensiform, with a prominent single vein on upper side; middle leaflets are longer, up to 600 mm long.
Male and female inflorescences are 5 m or more long and armed with claws. The flagellum is attached here (this is a whiplike climbing organ bearing reflexed strong claws on the lower side). Partial inflorescences occur which are about 1 m long with 3-4 rachillae on each side. The primary closely sheathing bract is tubular and fibrous at upper end. The rachillae are 100-250 mm long, each bearing 10-30 flowers. Male flowers are 8 - 10 mm x 3 mm, curved on the outside. Female flowers are about 7 mm long, with an ovate, 3-toothed calyx and lanceolate petals, positioned remotely on the rachillae (which are 200-250 mm long, truncate and projected from the basal bract). The fruit are about 30 mm long, broadly ovoid with fruit scales deeply channelled in the middle.[2]