keys to the vascular plants of east texas - Botanical Research ...

SPIRODELA/LEMNACEAE
723
Lemna turionifera Landolt, (turion-bearing), DUCKWEED, TURION DUCKWEED. Fronds floating,
ovate to nearly orbicular, 1.5–4 mm long, 1-1.5 times longer than wide, with 3 veins; plant producing
small obovate to circular, rootless, dark green to brown turions (for overwintering); roots
1–6(–15) cm long, the root sheath not winged. Bowie Co. (Landolt 1986) in ne corner of East TX
and Hays Co. (Landolt 1986) on the sw margin of East TX; also Aransas Co. in Gulf Prairies and
Marshes, Donley, Hemphill, Lipscomb, and Oldham cos. in the Rolling Plains, Kerr Co. on the
Edwards Plateau, El Paso Co. in the Trans-Pecos (Landolt 1986), and Real Co. (Turner et al. 2003)
on the Edwards Plateau; widespread in Canada and most of the U.S. but rare in the se U.S.
Lemna valdiviana Phil., (of Valdivia, Chile), VALDIVIANA DUCKWEED, PALE DUCKWEED. Fronds
floating or rarely submersed, ovate to lanceolate, somewhat falcate to symmetrical except for
the oblique base, mostly (1–)2.5–5 mm long, 0.6–3 mm wide, 1.3–3 times longer than wide, occasionally
somewhat pointed, light green, flat to slightly biconvex, with 1 vein; turions absent;
roots 0.5–1.5 cm long, the root sheath not winged. Widely scattered in TX except in the nw and
s parts of the state; widespread in the se U.S., scattered elsewhere. This species and L. minuta are
considered the most morphologically reduced species in the genus Lemna (Landolt 1986).
Lemna trisulca L., (three-furrowed), STAR DUCKWEED, IVY DUCKWEED, IVY-LEAF DUCKWEED, was
included for TX by Correll & Johnston (1970) with the comment “reported from Tex.” It was
also cited for the Pineywoods and Gulf Prairies and Marshes by Hatch et al. (1990). However, we
have been unable to find any confirming specimens, and Landolt (1986, 2000) gave no citations
for TX. While the species is thus probably not a member of the TX flora, it is mentioned here as
a note to encourage collectors to look for it; it occurs widely in Canada, throughout most of the
n 1/2 of the U.S., and is scattered further s. Plant submersed, usually forming tangled masses
just below the water surface; fronds 3–15 mm long excluding conspicuous stalk-like bases, narrowly
ovate to oblong, abruptly narrowed to the stalk-like bases, � flat, often with reddish pigmentation,
the margins usually minutely toothed near apex. Quiet, calcium rich waters, in
cool-temperate regions (Landolt 2000).
SPIRODELA Schleid. DUCKMEAT, DUCKMEAL, BIG DUCKWEED
AA cosmopolitan genus of 2 species (Les & Crawford 1999; Landolt 2000). Landoltia punctata
was previously included in Spirodela; however, recent studies (see discussion under Landoltia)
indicate that it should be recognized as a distinct genus. Spirodela is the least reduced genus in
the family. It is sometimes grown, using dairy waste water, as a substitute for alfalfa in animal
food. (Greek: speira, coil, twist, or spiral, and delos, evident, visible, or distinct, from the roots)
REFERENCES: Krajncic & Devidé 1979; Crawford & Landolt 1993; Les & Crawford 1999.
Spirodela polyrhiza (L.) Schleid., (many-rooted), COMMON DUCKMEAT, DUCKMEAT, GREATER DUCK-
WEED, BIG DUCKWEED. Fronds floating on water surface, solitary or in clusters of a few, orbicular-obovate
to nearly ovate, flat or rarely gibbous, 3–10 mm long, usually 3–6 mm wide, 1–1.5
times longer than wide (often almost as wide as long), with 7–16(–21) conspicuous veins, the
upper surface dark lustrous green, often with a conspicuous red dot near center, without distinct
papillae, the lower surface usually reddish purple; roots (4–)7–21 per frond, 1–2(–3) perforating
a membranous scale (= prophyllum); turions sometimes present; vegetative reproductive
pouches 2 per frond, these lateral near frond base; flowers 1(–2) per frond, but seldom flowering.
Quiet waters; widespread in TX but more common in the e 1/2 of the state; this species is more
widespread and abundant in East TX than is the somewhat similar Landoltia punctata; widespread
in s Canada and nearly throughout the U.S. This species is the largest of the surfacefloating
duckweeds.