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Classification
Calamus
Nomenclature
SUMMARY
Solitary or clustering, stemless to high-climbing or erect pleonanthic dioecious rattans; sheaths usually heavily armed with spines, the spines frequently highly organised. Flagellum (sterile inflorescence) often present, borne on the leaf sheath, sometimes absent and replaced by a cirrus at the end of the leaf, very rarely both present or both absent; knee often present; ocrea sometimes well developed, usually inconspicuous. Male and female inflorescences superficially similar, often ending in a long flagellum, sometimes with gradual succession of branches, often with discrete distant branches (partial inflorescences); bracts always tubular at the base, rarely with broad limbs splitting down one side, but if so, then the base always tubular and unsplit, bracts variously armed; partial inflorescences usually much longer than the subtending bract, very rarely shorter, floral bracteoles inconspicuous. Male flower solitary in each rachilla bract, with cup-shaped calyx, usually with 3 well defined lobes; corolla split almost to the base into 3 petals; stamens 6 (very rarely 12), very shortly epipetalous; pistillode minute. Female flower borne together with a sterile male flower as a pair. Sterile male flower like the fertile male, but with empty anthers. Female flower usually larger than the male, with calyx shallowly 3-lobed; corolla with 3 petals; staminodes 6, joined basally to form a ring; ovary tipped with 3 stigmas and covered with reflexed scales; locules 3 with one ovule in each. Fruit variously shaped, covered in reflexed scales. Seed usually one only, rarely 3 developing, very variable in shape, covered in a thin to thick sarcotesta; endosperm homogeneous or ruminate; embryo basal or lateral. Seedling leaf bifid or pinnate.
About 388 species: Africa, India and South China, Sri Lanka, southwards through the Malay Archipelago to Australia and Fiji. Reaches its greatest diversity in Peninsular Malaysia and Borneo with a secondary centre of diversity in New Guinea. Fifty one species with two subspecies and two varieties in Thailand.
Calamus can only be identified to genus by a combination of characters. Together with Ceratolobus, Daemonorops and Pogonotium it forms a group of closely related genera in which the female inflorescence bears dyads – pairs of flowers, each consisting of a female flower together with a sterile male flower – while the male inflorescence bears male flowers singly. The differences between these genera are based mostly on the overall structure of the inflorescence, in particular the nature of the bracts. The most reliable character separating Calamus is the persistent tubular nature of the bracts. Some generalisations can be made – rattans with flagella must belong to Calamus, though not all species of Calamus bear flagella. Rattans with subcirrate leaves are usually species of Calamus. If the endosperm is homogeneous, then the rattan cannot belong to Daemonorops, but ruminate endosperms are found in both genera. The differences are summarised in the key to genera. With practice the genera are eventually easily distinguished.