[Arisaema-l] Arisaema root structure

[Jim McKenney]

Eric noted Murata's paper Diversity in the Stem Morphology of Arisaema. 

The important word here is "stem".

The thing which sprouts above ground and supports the leaves and inflorescence of an Arisaema is an annual stem, sometimes called a pseudostem. That is not the stem we are talking about here. The stem we are talking about here is the perennial stem, the structure variously called a corm, tuber, rhizome and so on. 

If you define "corm" as an abbreviated modular stem, then that definition fits what we see in Arisaema well. The "modular" part is important to the definition; this is what distinguishes a corm from a rhizome. Corms are compact, ultimately separate and discrete entities. It's that separateness which makes them corms. Rhizomes are attached to the source plant and are thus not modular. But when rhizomes become detached from the source plant, they in effect become elongated corms. Corms more than likely originated as rhizomes became more and more compact, and in the Iridaceae in particular there are all sorts of gradations between typical corm and typical rhizome to be seen.  

In the plant family Colchicaceae, one can see plants with typical corms (as in many members of the genus Colchicum) and plants with elongated structures which at first glance suggest rhizomes but on further examination are seen to be elongated corms (as in the genus Gloriosa or in some Merendera). 

True bulbs have a structure traditionally called the basal plate. This basal plate is the true perennial stem of the plant. It is in effect a corm (i.e. a stem) at the center of the bulb. Bulbs can be thought of as corms with the addition of fleshy storage organs derived from modified leaves. 

There have been extensive discussions of this topic on the Pacific Bulb Society forum.

The words corm, bulb, rhizome and others have usefulness in some contexts, and what they have in common is that they refer to the true perennial stem of the plant. So  I'm retraining myself to think of all of them primarily as the true perennial stem of the plant in question, and to modify that as "the perennial stem is cormous" or "the perennial stem is bulbous" or "the perennial stem is rhizomatous" and so on. 
Jim McKenney
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________________________________
 From: Erick Adams <rogthegoat at hotmail.com>
To: arisaema-l at science.uu.nl 
Sent: Sunday, April 22, 2012 9:27 AM
Subject: Re: [Arisaema-l] Arisaema root structure
 

 
Arisaema taxonomist Jin Murata published a paper called Diversity in the Stem Morphology of Arisaema.
I have not read the paper proper but the opening abstract refers to the pertinent 
underground bits as an "abbreviated subterranean stem".
 
I think that's a good way to put it so we don't have to figure out where a tuber begins, 
a corm ends and to what degree they are rhizotamous. Hoozah.
 
It also provides a mildly amusing acronym for making bad Arisaema jokes.
 
 
Erick 
 
Zone 6 - Rhode Island, USA
 
 
 


________________________________
Date: Sun, 22 Apr 2012 07:58:44 +0100
From: petersirises at gmail.com
To: arisaema-l at science.uu.nl
Subject: [Arisaema-l] Arisaema root structure


What is the botanical term for the storage organ on an Arisaema please?

I think of it as a tuber which is a swollen root such as a potato has, but a potato is a dicot. Is the 'tuber' root or stem? Were it stem then surely it would count as a rhizome -as with a bearded Iris?  Others here are calling it a corm, I associate corms with Irids and regard them as stems surrounded by compressed leaves.
An article by Tony Avant refers to it as a pseudo tuber...


Peter (UK)
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