Can anybody tell me the difference between the genus Lemna sp. and
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?
"Edgar Heim" <e.h...@bluewin.ch> wrote in message
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.
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
_Lemna_ (and _Spirodela_) inflorescences consist of *two staminate* (male)
and one carpellate (female) flower, subtended with a spathe (a reduced
_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
Edgar Heim schrieb in Nachricht <38553a52...@news.bluewin.ch>...