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Stems solitary or clustered, mostly slender and climbing, occasionally non-climbing. Leaves 10-60, pinnate, spiny, sheaths closed in climbing stems, open in non-climbers, variously hairy and spiny, pinnae variously arranged and shaped. Plants dioecious. Inflorescence branched to 3 orders, branches and rachillae covered with overlapping bracts, bracts variously armed.  Male flowers : calyx cup-shaped,  petals 3, stamens 6, pistillode minute. Female flowers : calyx shallowly 3-lobed, petals 3, staminodes 6,  ovary tipped with stigmas. Fruit variously shaped and coloured, always covered with overlapping scales. Seed usually 1.

Key to the species

Serial Key Reference
1a. Leaf-sheath flagellate or leaf rachis cirrate 2
1b. Leaf-sheath not flagellate or leaf rachis not cirrate 6
2a. Leaf-sheath flagellate 3
2b. Leaf rachis cirrate. Leaflets alternately clustered in 2s ( one or two leaflets solitary towards base), 4 -5 cm wide, glabrous on both surfaces Calamus latifolius
3a. Leaflets in regular intervals, not in groups 4
3b. Leaflets not in regular intervals, solitary to in groups of 2, 3 or 4 5
4a. Slender horizontal spines crowded with smaller spines in- between in leaf-sheaths; ocrea distinct, membranous, lacerate; primary bract split and laminated Calamus guruba
4b. Slender horizontal spines not crowded with smaller spines in- between in leaf-sheaths; ocrea indistinct, not membranous nor lacerate; primary bract tubular, never split or laminated Calamus tenuis
5a. Leaf-sheaths, rachis and young leaflets floccose; stem with sheath 3-4 cm, and without sheath 1-3 cm in diameter; leaves 90-100 cm long; knee conspicuous in on the leaf-sheath Calamus viminalis
5b. Leaf-sheaths, rachis and young leaflets not floccose; stem with sheath 1.0-1.5 cm, and without sheath 0.6-0.4 cm in diameter; leaves 30-70 cm long; knee very slight or conspicuous in on the leaf-sheath Calamus gracilis
6a. Stem erect, diameter with sheath more than 10 cm; ocrea tubular, fibrous, extending more than 30 cm along the petiole margin, split and bifurcate at top, hispid; leaflets equidistant Calamus erectus
6b. Stem spreading to climbing, diameter with sheath less than 10 cm; ocrea not tubular, not fibrous; leaflets grouped in 2s or 3s up to the upper end of the rachis Calamus longisetus