Difference between Lemna sp. and Wolffia sp.

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Edgar Heim

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Dec 13, 1999, 3:00:00 AM12/13/99
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Hello

Can anybody tell me the difference between the genus Lemna sp. and
Wolffia sp.?
I'm wondering, if the difference is the root. Lemna minor has a root
and Wolffia arrhiza none. Arrhiza means without root. Is this a
species-difference or is it the difference of the genus?

Thanks Edgar

Monique Reed

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Dec 13, 1999, 3:00:00 AM12/13/99
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I believe that Wolffia in general are rootless, and much smaller, than
Lemna.

M. Reed

J. Kelly

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Dec 14, 1999, 3:00:00 AM12/14/99
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It's true that at least here in the U.S. Wollfia lacks roots while Lemna has
roots. But actually the leaves look quite a bit different. Wollfia leaves
are incredibly tiny and the plants look like little roundish balls
(approximately 1 mm in diameter) floating on the water.
Lemna has distinctly flattish leaves with roots dangling beneath. Lemna
minor floats on the surface while Lemna trisulca is submerged. A third
genus, Spirodela, may be found with Lemna minor. Spirodela leaves are a
solid dark purple on the underside, while Lemna leaves are green on the
underside. All three genera often grow in the same pond. Hope this helps
you.
Judy Kelly, Biology Dept., Henry Ford College, Dearborn, MI

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Stephen M Jankalski

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Dec 14, 1999, 3:00:00 AM12/14/99
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Dear Edgar,

Here is a key to the genera of Lemnaceae.

Plants with roots and two reproductive pouches.
Roots two or more per frond................Spirodela Schleid.
Root one per frond..............................Lemna L.
Plants without roots and with one reproductive pouch.
Fronds globular or ellipsoid.................Wolffia Horkel
Fronds sickle-shaped and elongated....Wolffiella Hegelm.

I'm surprised that you could not find anything about them in any floras.
See: Harrison, D.E. & Beal, E.O. (1964) THE LEMNACEAE OF NORTH CAROLINA.
Journ. Elisha Mitchell Sci. Soc. 80: 12-18. for more information.

Cereusly Steve

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

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chrisroesch

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Dec 19, 1999, 3:00:00 AM12/19/99
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Hello Edgar,

I would rather not see the difference between _Lemna spp._ and _Wolffia
spp._ in the presence/absence of roots. Most species of the Lemnaceae family
have no roots (although it's true that _Spirodela_ has several and _Lemna_
has one single "root" but all are lacking vascular tissue).

More important seems to be the composition of the inflorescences (flower
clusters):
_Lemna_ (and _Spirodela_) inflorescences consist of *two staminate* (male)
and one carpellate (female) flower, subtended with a spathe (a reduced
leaf).
_Wolffia_ (and _Wolffiella_) inflorecences on the other hand consist only of
*one staminate* and one carpellate flower *without spathe*.

For reference see e.g.:
Hartog C (1975). Thoughts about the taxonomical relationships within the
Lemnaceae. _Aquatic Bot._ *1* 407-416

Christopher Roesch
Cologne, Germany


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