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Re: Tubers, corms and bulbs, oh my!

  • Subject: Re: Tubers, corms and bulbs, oh my!
  • From: "Wilbert Hetterscheid" <hetter@xs4all.nl>
  • Date: Thu, 11 Feb 2010 16:54:44 +0100

My 2 cents of superfluous wisdom in this:

Tubers in Araceae are condensed stems with food-storage function. Such stems can also be elongate and creeping and then we call then rhizomes. In Araceae rhizome and tuber are two parts of a "continuum". One the one extreme are long creeping rhizomes with numerous long internodes. Condensaton of the internodes give us shorter rhizomes. Reduction of the number of internodes gives us shorter rhizomes (meaning mostly that the decay of older internodes is fast). We may find very short rhizomes (one or two internodes), which because they may be thicker than long, look "tuberous" (Typhonium). Also internodes may be way shorter than their width, which also gives the rhizome a kind of tuberous look (e.g. Arum). And then finally there's rhizomes that produce one internode in a season and at the same time devour the previous internode and they may also decide to grow vertically. That's what we see in e.g. most Amorphophallus and e.g. Sauromatum, several Arisaema. In these genera often few or more species are in fact fully rhizomatous, which goes to show how easily one state changes or reverts to another. In Amorphs there is even a fully genus-exclusive extra: the one-nodal-rhizome (we call tuber) may elongate vertically, not by creating extra nodes but by elongation of the one node present (A. longituberosus and like). 

My opinion is that "tuber" in Aroids (and in many other families) is more of an "appearance" term, than a truely reliable systematic term. Aroids have stems, which may be creeping, food storing [but not always] and semi- of fully subterranean and then are called rhizome. The shape and structure of a rhizome may be so that it looks like a tuber (and my guess is that "tuber" is an ancient relict word for a food-bringing underground plant part, and as such a human-usage driven term).

So, a majority of Amorphs have an upright, subterranean, one-nodal rhizome and we call that a tuber. The best illustration of the "ancient" condition is in Am. coaetaneus, where a chain of swollen, "tuber like" nodes is present. This species has decided not to devour old nodes but keep them intact, so a chain of "tubers" develops (see IAS website under this species) and this chain is in fact again a full scale rhizome. But in the same genus we can also find "normal" rhizomes with many nodes and equally thick all over (A. rhizomatosus, A. hayi). The conditions are therefore evolutionarily interchangeable because they are several sides of the same medal (strange medal THAT is.........).

Cheers,
Wilbert
 

   

> -----Oorspronkelijk bericht-----
> Van: aroid-l-bounces@gizmoworks.com 
> [mailto:aroid-l-bounces@gizmoworks.com] Namens Marek Argent
> Verzonden: donderdag 11 februari 2010 0:12
> Aan: Discussion of aroids
> Onderwerp: Re: [Aroid-l] Tubers, corms and bulbs, oh my!
> 
> Dear Vincent,
>  
> A rhizome is a stem (erect or creeping) with very shortened 
> internodes.
> Calla palustris, Anubias spp, Xanthosoma violaceum.
> And the best it is visible in large Alocasia spp. 
> Here's an example: 
> http://www.wschowa.com/abrimaal/araceum/alocasia/odora.htm
>  
> Marek
> 
> 	----- Original Message ----- 
> 	From: E.Vincent Morano <mailto:ironious2@yahoo.com>  
> 	To: Discussion of aroids <mailto:aroid-l@gizmoworks.com>  
> 	Sent: Tuesday, February 09, 2010 12:02 AM
> 	Subject: Re: [Aroid-l] Tubers, corms and bulbs, oh my!
> 
> All good info! But this begs the question. What then is a 
> rhizome? it doesnt look like tuber corm nor bulb. 
> 
> 
> 
> 
> 
> I refuse to participate in the in the recession.
> 
> --- On Thu, 2/4/10, Christopher Rogers 
> <crogers@ecoanalysts.com> wrote:
> 
> 
> 
> 	From: Christopher Rogers <crogers@ecoanalysts.com>
> 	Subject: [Aroid-l] Tubers, corms and bulbs, oh my!
> 	To: "'Discussion of aroids'" <aroid-l@gizmoworks.com>
> 	Date: Thursday, February 4, 2010, 11:02 AM
> 	
> 	
> 
> 	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
> 
> 	((,///////////=======<
> 
> 	branchiopod@gmail.com 
> 
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> 
> 
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