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2010/2/4 Christopher Rogers
Hiyer!
Irecently had a discussion with few Aroid Oriented Individuals about properterminology for the non-root, subterranean aroid parts. Or to put it anotherway, do plants like Amorphophallus, Arum, Helicodiceros, Typhonium, Colocasia,Ambrosina, and the like have tubers, corms or bulbs?
Theanswer is that they have tubers. (Or for dear Julius’ sake, “chubas”).
Abulb is composed of thick, modified leaves, arranged in layers, for foodstorage. An onion is a perfect example.
Acorm is composed entirely of stem tissue. It is literally just an undergroundstem. It has an epidermal layer, a vascular cylinder with phloem and xylem andcentral pith. A corm can also be a starch storage organ, but it still has true stemtissue. This is why a corm has the new foliage growth coming from the top andthe roots coming from the base. Corm examples are Crocus, Cyclamen andGladiolus. A cormel is just a diminutive corm.
Atuber is just parenchyma (with some vascular tissue). It has an epidermal layerwith some subdermal vascular tissue, and all the rest is parenchyma. It isalmost entirely a starch storage organ. This is why the foliage and the rootsall come from the top. Most plants with tubers have them borne on stolons, butthat is not necessary. In Amorphophallus, Arum and Typhonium for example, thestem tissue is all encased in the small bud at the top of the tuber. That budgrows upward into a leaf or two, and outward into roots, with the tuberbeneath. Other tuber examples are potatoes and Sinningia.
Abulbil, in the aroid sense, is just a tuber that forms on leaves or leaf axils.It is an unfortunate term as it obviously leads to confusion.
Ireally hope that this is helpful to the Aroid community at large, and I hope itcuts down on some of the confusion surrounding these terms. I am sure Pete,Wilbert, Tom, Julius, The Banta or someone can elucidate further, particularlyas far as tuberous rhizomes or rhizomatic tubers are concerned.
Happydays,
Christopher
D.Christopher Rogers
SeniorInvertebrate Ecologist/ Taxonomist
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