International Aroid Society

Dear Christopher:

=9A=9A=9A=9A=9A=9A=9A=9A=9A=9A=9A That is an excellentdistinction that you made for the difference between tuber and corm.=9A I havealways assumed that the corm was non existent in Araceae since most storageorgans called stems are just a big bag of starch.

Tom

From:aroid-l-bounces@gizmoworks.com [mailto:aroid-l-bounces@gizmoworks.com] On Behalf Of Christopher Rogers
Sent: Thursday, February 04, 20101:02 PM
To: 'Discussion of aroids'
Subject: [Aroid-l] Tubers, cormsand bulbs, oh my!

Hiyer!

I recently had a discussion with fewAroid Oriented Individuals about proper terminology for the non-root,subterranean aroid parts. Or to put it another way, do plants likeAmorphophallus, Arum, Helicodiceros, Typhonium, Colocasia, Ambrosina, and thelike have tubers, corms or bulbs?

The answer is that they have tubers. (Orfor dear Julius’ sake, “chubas”).

A bulb is composed of thick, modifiedleaves, arranged in layers, for food storage. An onion is a perfect example.

A corm is composed entirely of stemtissue. It is literally just an underground stem. It has an epidermal layer, avascular cylinder with phloem and xylem and central pith. A corm can also be astarch storage organ, but it still has true stem tissue. This is why a corm hasthe 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 diminutivecorm.

A tuber is just parenchyma (with somevascular tissue). It has an epidermal layer with some subdermal vasculartissue, and all the rest is parenchyma. It is almost entirely a starch storageorgan. This is why the foliage and the roots all come from the top. Most plantswith tubers have them borne on stolons, but that is not necessary. InAmorphophallus, Arum and Typhonium for example, the stem tissue is all encasedin the small bud at the top of the tuber. That bud grows upward into a leaf ortwo, and outward into roots, with the tuber beneath. Other tuber examples arepotatoes and Sinningia.

A bulbil, in the aroid sense, is just atuber that forms on leaves or leaf axils. It is an unfortunate term as itobviously leads to confusion.

I really hope that this is helpful to theAroid community at large, and I hope it cuts down on some of the confusionsurrounding these terms. I am sure Pete, Wilbert, Tom, Julius, The Banta orsomeone can elucidate further, particularly as far as tuberous rhizomes orrhizomatic tubers are concerned.

Happy days,

Christopher

D. Christopher Rogers

Senior Invertebrate Ecologist/ Taxonomist

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