Acceptable Oxalis

Fri, 01 May 2009 11:06:12 PDT

On searching various botanical dictionaries and looking at the
literature pertaining to a wide range of geophytic plants, it is clear
that there is little consensus on what exactly a corm is. Different
contemporary scientists use different terms for the same structure in
the same plants (see Araceae), so if they do not agree there may be
little hope for us.

The definition that seems most exclusive and precise to me includes
the essential fact that the organ *replaces itself* each season: this
would include many irids (Freesia, Gladiolus, etc.), Tecophilaeaceae,
many "tuberous aroids", Gloriosa and even a few begonias as well. It
gets interesting when we see things like Dierama or Ferraria or even
some Amorphophallus species with "chains" of corms that persist for
several seasons. Are they still considered corms if they are
persistent in this way?

I read somewhere that indeed tulip bulbs (Calochortus, too, I think)
are different in that the bulb is derived from modified cataphylls or
prophylls rather than leaf bases, but I did not realize they replace

Since the stem tissue portion of a 'normal' bulb is not replaced each
season it would not qualify as a corm, even though some definitions of
corm simply say that it is stem tissue. Annual replacement is the key
distinguishing trait I think, even if it is not absolute in all cases.

This is a great topic but unfortunately there is a paucity of
authoritative work on defining and categorizing these structures.
There is a lot of work to be done in this area-- morphology is not
passe! Some are truly anomalous, as the rootstocks of some Dioscorea
species, which have confusing features of both stem and root tissue at
the anatomical level. The word "rootstock" is indispensable.


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