Hiyer!
I
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?
The
answer is that they have tubers. (Or for dear Julius’ sake,
“chubas”).
A bulb
is composed of thick, modified leaves, arranged in layers, for food
storage. An onion is a perfect example.
A 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.
A
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.
A
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.
I
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.
Happy
days,
Christopher
D.
Christopher Rogers
Senior
Invertebrate Ecologist/ Taxonomist
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