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Tubers, corms and bulbs, oh my!

  • Subject: Tubers, corms and bulbs, oh my!
  • From: ExoticRainforest <Steve@ExoticRainforest.com>
  • Date: Sat, 13 Feb 2010 15:02:20 -0600

Thanks Dylan! 

I have been trying to do a fair amount of research to better understand all these terms for the past 6 weeks.  I corresponded with Wilbert a few months ago and helped a great deal to make the subject clearer.  Tom also sent a number of corrections to some of my personal misunderstandings  so thanks to both of you along with Christopher and Tom for all these very clear explanations.

By the way Dylan, the IAS is growing and we need more authoritative voices on Aroid l..  Thanks a bunch for making your first contributions, please don't make it your last! 

All of us need good info rather than much of the mishmash found on the internet.  I'm certain the IAS board will back me up in thanking you, Tom, Wilbert, Pete, Eduardo, David, Simon, Marcus, Marc, Julius and all the authoritative voices that make sure we read good info!  The next issue of the IAS Newsletter will be out in about one month so if any of you on Aroid l haven't joined please take the time to do it now.   www.Aroid.org

By the way, I haven't read any responses to Ted Held's post regarding hearing some of Julius' personal stories.  If you missed that post you can find it here: 

I have already listened to his narration about Christmas dinner in Trinidad and strongly suggest all of you that have read Julius' great posts but never had the pleasure of hearing his voice visit the site!  It is a riot, and that does not count for the fact our old Aroid l  friend is incredibly brilliant!

Thanks again!

Steve Lucas

Hannon wrote:
Thanks to Wilbert for a very good synopsis of 'compact rootstocks' or
tubers in Araceae. As a first time Aroid-Ler and longtime aroider I
would like to offer a few comments.

I think what Wilbert elaborates here makes perfect sense. My only
quibble is that if we make no use of existing descriptive terminology
then we use more words than we need to to describe things, or we use
words that have imprecise or vague meanings. If all these structures
are rhizomes or (apparently) derived evolutionarily from rhizomes,
that is very useful as a concept. Yet within this scheme there are
structures that can be differentiated, if arbitrarily, into more
narrowly defined notions such as tubers, rhizomes and corms.

Some of us are weary of any confining definitions altogether. In the
case of rootstocks especially it is difficult to imagine any taxonomy
that could capture and discretely name the different types found in
nature. In fact it has not been done. Still, it seems to me that a
corm is something quite distinct, even if its origins are betrayed by
peculiar congeners, as in Wilbert's Amorphophallus example. Any
modular unit that may resemble a tuber or bulb and _replaces itself
each growing season_ can rightfully be called a corm, regardless of
the number of nodes/internodes involved or features of tunics vs.
naked flesh. Annual replacement is the key trait of a corm.

Other families exhibiting "true" corms that are replaced annually
(sources in the botanical literature give inconsistent definitions)
are the iris family (Gladiolus, Crocus, etc.), Themidaceae (Brodiaea,
Milla, etc.) and some Cyanastraceae/Tecophilaeaceae. "Chains of
tubers" can be found in Dierama and probably others and perhaps
similar ontogenic processes have been at work in these families. As
far as I know the rootstocks of these plants have traditionally, in
botany, been labeled "corm" and not tuber or bulb. This concise
designation continues to serve a useful purpose for the scientist and
layman alike. As Wilbert indicates, we have "traditionally" called the
tuber-like structures in aroids, well, tubers.

If we say there is only a morphological continuum, or that all the
rootstock types in a group are basically rhizomes, then clarification
and elucidation are sacrificed.

Dylan Hannon

fn:Steve  Lucas

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