The Lemnaceae are the structurally simplest of the flowering plants.
The plants are not differentiated into stems and leaves; instead, the
plants in the family have an undifferentiated leaf-like body commonly
referred to as a frond or thallus. The most recent treatment of the family
by Landolt (1986) recognizes 34 species in the genera Spirodela, Lemna,
Wolffiella, and Wolffia. Other treatments of the family include those
of Hartog and Van der Plas (1970) and Daubs (1965).
The various genera in the Lemnaceae can be distinguished by the following
Plants usually with 2 to several roots on the lower side of the fronds;
under surface of the frond usually reddish; nerves 3 to 15 and usually
Plants with 1 root on the lower surface side of the fronds (except L.
trisulca which is often rootless); the under surface of the frond green
or streaked with brown; nerves 1 to 3, often indistinct
Plants rootless; fronds thick, globoid to ovoid, boat- or nutshell-like,
barely discernible to the naked eye
Plants rootless; fronds thin, essentially flat, ovate to linear, often
asymmetrically curved, easily visible
According to the treatment of Landolt (1986), nine species of Lemna occur
in the United States. With the exception of L. trisulca L., which is attached
to the parent plant by a narrow stipe, identification of the various species
of Lemna is often difficult. The treatment of Landolt (1986) also includes
some names of species that are not in usage in regional floras that predate
Landolt’s monographic study. For these reasons, this system does
not attempt to separate the various species of Lemna, except for L. trisulca
which is readily distinguishable from the other species of Lemna. The
user of this system should consult a regional flora manual to distinguish
the various species of Lemna.
The common name comes from its size relative to that of the other common
North American duckweed, Greater Duckweed (Spirodela polyrhiza).