Solitary or clustered, spiny, acaulescent, erect, or high-climbing, pleonanthic, dioecious, rattan palms. Stem eventually becoming bare, with short to long internodes, sucker shoots strictly axillary. Leaves pinnate, rarely bifid, sometimes with a terminal cirrus; sheath splitting in acaulescent species, in the exposed area usually densely armed with scattered or whorled spines, in one species (Calamus polystachys) the spines interlocking to form galleries occupied by ants, indumentum often abundant on sheath surface; ocrea often present, sometimes greatly elaborated, papery and disintegrating, or coriaceous, rarely greatly swollen or diverging with inrolled margins and occupied by ants; knee present in most climbing species; flagellum (climbing whip derived from a sterile inflorescence) often present in species lacking cirri, very rarely a small vestigial flagellum present in cirrate species (e.g., C. pogonacanthus); petiole absent or well developed, flattened adaxially, rounded abaxially, variously armed; rachis often armed with distant groups of reflexed grapnel spines; cirrus when present armed with scattered (rarely) or grouped reflexed spines; leaflets few to very numerous, single-fold, entire or in 1 species praemorse (C. caryotoides), linear to lanceolate or rhomboid, sometimes the terminal pair partially joined along their inner margins forming a terminal compound leaflet or flabellum, regularly arranged or irregular, grouped, sometimes fanned within the groups, concolourous or discolourous, variously bearing hairs, bristles, spines, and scales, midribs conspicuous or not, transverse veinlets conspicuous or obscure. Inflorescences axillary but adnate to the internode and leaf sheath of the following leaf, staminate and pistillate superficially similar, but the staminate usually branching to 3 orders and the pistillate to 2 orders, the inflorescence frequently flagelliform, very rarely rooting at its tip and producing a new vegetative shoot; peduncle absent or present, sometimes very long, erect or pendulous, variously armed; prophyll usually inconspicuous, 2-keeled, tubular, tightly sheathing, variously armed or unarmed, rarely inflated, papery or coriaceous, splitting down one side, usually empty; rachis bracts persistent, like the prophyll, close or sometimes very distant, variously armed, usually strictly tubular, even where splitting remaining tubular at the base, rarely irregularly tattering in the distal part, each subtending a first-order branch or ‘partial inflorescence’, this frequently adnate to the rachis above the bract axil, very rarely bursting through the bract; first-order branch bearing a 2-keeled, tubular prophyll and ± subdistichous, tubular bracts, unarmed or variously armed, each subtending a second-order branch, usually adnate to the first-order branch above the bract node; rachillae very varied within the genus, spreading to very short and crowded, bearing a basal, 2-keeled prophyll and conspicuous, usually distichous, tubular bracts with triangular tips, variously armed or unarmed, very rarely the bracts highly condensed and spiral, in staminate rachilla, each bract subtending a solitary staminate flower bearing a prophyllar bracteole, in pistillate rachilla each bract subtending a dyad of a sterile staminate and a fertile pistillate flower and 2, usually quite conspicuous, prophyllar bracteoles, very rarely each bract subtending a triad of 2 lateral pistillate flowers and a central sterile staminate flower. Staminate flowers symmetrical; calyx tubular at the base, 3-lobed distally; corolla usually exceeding the calyx, divided into 3, valvate lobes except at the tubular base; stamens 6 (12 in Calamus ornatus), borne at the mouth of the corolla tube, filaments often fleshy, elongate, sometimes abruptly narrowed, anthers medifixed, short to elongate, latrorse or introrse; pistillode minute to quite conspicuous. Pollen ellipsoidal, bi-symmetric; apertures equatorially disulcate; ectexine tectate or semi-tectate, psilate, perforate, coarsely perforate, foveolate, finely to coarsely reticulate, reticulate-rugulate, verrucate, gemmate or, rarely, ectexine intectate with large, loosely attached, psilate gemmae,aperture margins usually similar to surrounding ectexine; infratectumcolumellate; longest axis 17–67 µm; post-meiotic tetrads tetragonal[104/363]. Sterile staminate flowers like the fertile but with empty anthers.Pistillate flowers usually larger than the staminate; calyx tubular, shallowly3-lobed; corolla rarely exceeding the calyx, divided more deeply than thecalyx into 3 valvate lobes; staminodes 6, epipetalous, the filaments distinctor united into a short ring, anthers empty; gynoecium tricarpellate,triovulate, spherical to ellipsoidal, covered in reflexed scales, stigmas 3,apical, fleshy, reflexed, sometimes borne on a beak, locules incomplete,ovules basal, anatropous. Fruit usually 1-seeded, rarely consistently 2- or3-seeded, stigmatic remains apical; epicarp covered in neat vertical rowsof reflexed scales, mesocarp usually very thin at maturity, endocarp notdifferentiated. Seed with thick sweet, sour, or astringent sarcotesta, innerpart of the seed rounded, grooved, angled, or sharply winged, endospermhomogeneous or ruminate; embryo basal or lateral. Germination adjacent-ligular; eophyll bifid or pinnate. Cytology: 2n = 26.
Immensely variable genus of mostly climbing palms, some acaulescent or erect, found in equatorial Africa, India, Himalayan foothills to south China, throughout Southeast Asia to the western Pacific Islands and Australia; sheaths, petioles and rachis usually densely armed, leaf often terminating in a cirrus armed with spines, or cirrus absent; flagellum sometimes present (sterile inflorescence modified as a climbing organ); pleonanthic and dioecious, the inflorescence is very varied but bracts are usually tubular, sometimes splitting, but if so, never to the base and never caducous.
The ecology is very varied as might be expected in such a large genus, but, although some species are adapted to seasonally dry habitats such as monsoon forest, there are no species in semi-arid habitats. There are species adapted to sub-mangrove conditions (C.erinaceus). Other species have narrow ecological requirements, such as limestone or ultrabasic soils. In altitude, the genus ranges from sea-level to over 3000 m (C. gibbsianus on Mt Kinabalu).
With about 374 species, Calamus isthe largest palm genus. It has a very wide distribution, occurring in the humid tropics of Africa (one variable species), India, Burma, and south China through the Malay Archipelago to Queensland and Fiji, reaching greatest diversity and number of species in the Sunda Shelf area (especially Borneo), with a second centre of diversity in New Guinea.
The finest kinds of rattan are all species of Calamus. C. manan, C. caesius, and C. trachycoleus, in particular, dominate world trade in rattans. Other species are almost as important. For further details of rattans and their exploitation see Dransfield 1979a. Species of Calamus have a wide range of uses apart from entering the rattan trade. Leaves are used for thatch, spines in various ways, cirri have been used for constructing fish traps, fruits are eaten and may even be sold in local markets, and some species may be medicinally valuable.