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Not that I'm all that concerned with the exact
botanical term that accurately describes the 'tater our Amorphs grow from, but
surely we can all agree that if we unpot or dig up our Amorph species carefully
it is not at all uncommon to see roots coming from other than the top of the
underground thingy. I find it rather common for the long rhizomatous
growths to have roots coming out all along them, at least when I pay
attention. So, does this mean that the original description for a tuber
posited below needs to be revised or we need to rethink what we call it?
It seems the definition is not so simple for the botanists out there.
Since I learned it as a tuber when I first got my original A. konjac many years
ago I'm perfectly happy with that term, but it seems from the posts it is a bit
of a hornets nest.
Dan
Gibsonia, PA where we got a nice 75cm coating of
snow in the past 5 days....spring truly was 6 weeks away :o)
----- Original Message -----
From:
j*@Vanderbilt.Edu
To: aroid-l@gizmoworks.com
Sent: Monday, February 08, 2010 3:02
PM
Subject: Re: [Aroid-l] Tubers, corms and
bulbs, oh my!
Greetings,
While I
would agree that the recent discourse on tubers vs. corms certainly makes
clear an excellent distinction, the difficulty I have with it is that this is
not what many sources suggest. Several
examples:
From
Swartz, D. 1971. Collegiate Dictionary of
Botany:
Tuber – a relatively short thickened rhizome with numerous buds as
in the potato; a subterranean stem which is shorter and thicker than the root
stock
Corm – a solid fleshy underground base of a stem, usually somewhat
spherical in shape, covered with thin membranes. It serves for storage of
reserve food materials and resembles a bulb in appearance but not in
structure
From Radford, A.E., Ahles,H.E., & Bell, C. R..
1964. Manual of the Vascular Flora of the Carolinas:
Tuber – a fleshy
enlarged portion of rhizome or stolon with only vestigial scales; true tubers
found in the Solanaceae
Corm – a bulb-like structure in which the fleshy
portion is predominantly stem tissue covered by membranous scales
And
within the text, from Family 31. Araceae (The family description begins)
Perennial herbs from rhizomes or corms...
From Radford, A.E., Dickison,
W.C., Massey, J.R., Bell, C.R. 1974. Vascular Plant Systematics:
Tuber – a
thick storage stem, usually not upright
Corm - the enlarged, solid,
fleshy base of a stem with scales; an upright underground storage
stem
And from Stearn, W.T. 1983 (3rd Edition, revised) Botanical Latin:
Tuber – (in part) tuber large globose or irregular, with flesh whitish
bitter
Corm - literally ‘a trunk’; - for the solid bulb-like stem-base of
monocotyledons, the older authors, e.g. Ker-Gawler, used bulbo-tuber; cormus
magnus sub-globosus 5 cm. crassus tunicis brunneis membranaceis, corm large
almost globose 5 cm. thick, with tunics brown membranous.
There is no
debate regarding bulbs – a bulb is an underground storage structure comprised
of thickened foreshortened leaves all attached to a basal stem disc. But with
the real debate at hand, whether what we are looking at, definitely a modified
stem of some sort (and the sort is not uniform across all the genera
mentioned, nor even always within the same genus) is corm or tuber is I would
say still up for debate, depending on who’s definition of the terms one wants
or decides to choose.
As for rhizomatic(?) (rhizomatous) tubers or
tuberous rhizomes, I’m sure others may have a more serious vested interest in
this debate, but to me they’re both one type of stem serving as an adjective
for another type of stem, and which one chooses to put first is more a matter
of semantics, or else simply which aspect of the stems growth one notes as
being more significant, or maybe simply which was noted first. This of course
is not the case with the example of a sweet potato, which is a tuberous root,
i.e a root structure that closely resembles a tuber. Though by no means the
only difference, a major part of the difference here is how the vascular
tissue is arranged. Between stem type ‘a’ and stem type ‘b’ the challenge may
be a bit more difficult because in both of them the vascular tissue conforms
to the stem type arrangement. This vascular tissue is amply present in both,
perhaps even more so in the tuber since tubers typically have more than one
eye, i.e a new stem starting point. And although I am sure that there are
examples within the aroid genera mentioned, since the Sinningia genus
(Gesneriaceae) was also cited for tubers and I am even more well acquainted
with these I would point out that roots grow out from many different areas of
the tubers, definitely not just from the top.
Not to purposely remuddy
the waters, but there it is. Happy days, and good
growing.
Jonathan
On 2/4/10 1:02 PM, "Christopher Rogers" <crogers@ecoanalysts.com>
wrote:
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
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