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Calamoideae is a subfamily of flowering plant in the Arecaceae family found throughout Central America, South America, Africa, India, China, Southeast Asia and Australia. It is represented by 21 genera - containing nearly a quarter of all species in the palm family - including the largest genus, Calamus, the type genus of the group. Only four are found in the New World while the rest are Old World denizens, usually found in equatorial swampland or along tropical coastlines.
While the many species show marked differences, the bracts of all orders are tubular, the flowers are almost always borne in dyads or dyad derivatives, but most marked as an identifier among these palms are the overlapping scales covering the fruit; occasionally small and irregular they are, in most cases, neatly aligned in vertical rows. Also common to the group are varying forms of armament: spines along leaf margins or on sheaths, root and stem spines, reflexed rachis cirri, or specialized hooks among the climbing species.
The long fossil record and the many unspecialized features imply the group diverged early, parallel perhaps, with the Coryphoideae from an ancient protopalm ancestor. While the simplest floral characteristics belong to those rattan genera endemic to Africa ( Laccosperma, Eremospatha and Oncocalamus), they exhibit tremendous diversity suggesting a larger representation in the past. This subfamily has been noted in palm literature as the Lepidocaryoideae, however an 1844 (Griffith) designation of Calamoideae predates the use of the former at this rank and, as such, is correct in botanical nomenclature.
The leaf are consistently reduplicate of which palmate and pinnate variations exist. The armament on the leaves in many species mimics the armament found on other parts of plants in the group. Sharp prickles and spines line rachises, leaf margins and leaf sheaths. Other genera produce spines along the roots and stems. In climbing plants there are extended rachises formed into sharp spines while, as in the African rattans, the distal most leaflets are modified into reflexed spines, acanthophylls. While some Calamus species bear protective cirri others have evolved spines on false inflorescences as a means of protection.
Sexually they show hermaphroditic, monoecious, dioecious and polygamous characteristics of which some are hapaxanthic, dying after they flower and fruit, while the remainder follow the more common pleonanthic reproductive behavior, continuing growth after flowering. A bract is characteristic in this subfamily, protecting the dyads of flowers on maturing and where dyads are not present a dyadic origin of flowering is evident (with the exception of Oncocalamus). Triads of hermaphroditic flowers are occasionally discovered within Laccosperma and a sterile staminate flower winged by two pistillate flowers are found in the rare Calamus species though these are exceptions to the rule. Pollinated flowers produce a fruit with overlapping scales. Usually arranged in distinct, vertical rows, the scales in Eugeissona, Myrialepis and a handful of Salacca species are small and irregularly arranged.
In Africa they are plentiful south of the Sahara, reaching from the West across humid rain forest and the Congo Basin, through the central part of the continent with southern bands hugging the coast down through Angola to the west and Mozambique to the east; one species in the Raphia genus occupies areas across the northern part of Madagascar, another possible introduction.
Onto Sri Lanka, India, China, the Fiji and island chains and Australia, members of this subfamily are widely dispersed across East and West Asia and the southern Pacific.
Obsolete genera (all species are now included within the genus Calamus):
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