recently had a discussion with few Aroid Oriented Individuals about proper
terminology for the non-root, subterranean aroid parts. Or to put it another
way, do plants like Amorphophallus, Arum, Helicodiceros, Typhonium, Colocasia,
Ambrosina, and the like have tubers, corms or bulbs?
answer is that they have tubers. (Or for dear Julius’ sake, “chubas”).
bulb is composed of thick, modified leaves, arranged in layers, for food
storage. An onion is a perfect example.
corm is composed entirely of stem tissue. It is literally just an underground
stem. It has an epidermal layer, a vascular cylinder with phloem and xylem and
central pith. A corm can also be a starch storage organ, but it still has true stem
tissue. This is why a corm has the new foliage growth coming from the top and
the roots coming from the base. Corm examples are Crocus, Cyclamen and
Gladiolus. A cormel is just a diminutive corm.
tuber is just parenchyma (with some vascular tissue). It has an epidermal layer
with some subdermal vascular tissue, and all the rest is parenchyma. It is
almost entirely a starch storage organ. This is why the foliage and the roots
all come from the top. Most plants with tubers have them borne on stolons, but
that is not necessary. In Amorphophallus, Arum and Typhonium for example, the
stem tissue is all encased in the small bud at the top of the tuber. That bud
grows upward into a leaf or two, and outward into roots, with the tuber
beneath. Other tuber examples are potatoes and Sinningia.
bulbil, 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.
really hope that this is helpful to the Aroid community at large, and I hope it
cuts down on some of the confusion surrounding these terms. I am sure Pete,
Wilbert, Tom, Julius, The Banta or someone can elucidate further, particularly
as far as tuberous rhizomes or rhizomatic tubers are concerned.
Invertebrate Ecologist/ Taxonomist
P.O. Box 4098
Davis, CA 95616
IDAHO ∙ CALIFORNIA ∙ MISSOURI
∙ PENNSYLVANIA ∙ VANCOUVER
WWW.ECOANALYSTS.COM ∙ ECO@ECOANALYSTS.COM