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

720 LEMNACEAE/LANDOLTIA
REFERENCES: Thompson 1897; Hicks 1937; Maheshwari 1958; Wilson 1960; Harrison & Beal
1964; McClure & Alston 1966; Clark & Thieret 1968; den Hartog & van der Plas 1970; den
Hartog 1975; Landolt 1980, 1986, 1997, 1998, 2000; Urbanska-Worytkiewicz 1980; Dahlgren et al.
1985; Landolt & Kandeler 1987; Kvacek 1995; Mayo et al. 1995, 1997, 1998; Jordan et al. 1996; Les
et al. 1997, 2002; Stockey et al. 1997; Les & Crawford 1999; Yatskievych 1999; Bogner 2000;
Lemon & Posluszny 2000b.
1. Roots 1 or more per frond; fronds 2 mm long or longer, oblong to elliptic, ovate, obovate, or
orbicular, not long-tapered to apex, with 1 or more veins, usually floating on water surface.
2. Each frond with 1 root; fronds 2–6.5 mm long; pigment cells absent (discrete brown dots not
visible in dead fronds, but diffuse red pigmentation can be present) __________________________ Lemna
2. Each frond with several roots; fronds 2.5–10 mm long; pigment cells present (visible in dead
fronds as discrete brown dots; diffuse red pigmentation can also be present).
3. Roots (4–)7–21 per frond; fronds only 1–1.5 times longer than wide (often almost as wide
as long), 3–10 mm long, orbicular-obovate to nearly ovate, the upper surface often with a
conspicuous red dot near center, conspicuously several-veined with 7–16(–21) veins; species
widespread and abundant in East TX __________________________________________ Spirodela
3. Roots 2–7(–12) per frond; fronds distinctly longer than wide (1.5–2 times longer than wide),
1.5–5(–8) mm long, oblong-ovate to somewhat elliptic-reniform, the upper surface usually
without a conspicuous red dot, not conspicuously veined (with (3–)5–7 indistinct veins);
species apparently rare in East TX_________________________________________________ Landoltia
1. Roots absent; fronds EITHER < 1.6 mm long (pinhead size) OR fronds larger and ribbon-like to
tongue- or sabre-shaped or ovate, sometimes distinctly long-tapered from a relatively broad
base to a narrow apex, without veins, floating on water surface OR if not pinhead size, then
usually submersed just below water surface.
4. Fronds < 1.6 mm long, pinhead size, � distinctly 3-dimensional, never flat except on the upper
surface, unattached to one another or usually at most only two fronds attached together,
usually floating on the water surface __________________________________________________ Wolffia
4. Fronds usually 2–10 mm long, flat in cross section, membranous, rarely solitary to 2–many
attached together, usually floating just below the water surface ___________________________ Wolffiella
LANDOLTIA Les & D.J. Crawford DOTTED DUCKMEAT
AA monotypic genus (Les & Crawford 1999) previously included in Spirodela. However, based
on morphological, anatomical, flavonoid, allozyme, and rbcL sequence data, L. punctata is
“transitional between, but not a member of either Lemna or Spirodela” and “represents an isolated
clade distinct from both Spirodela and Lemna” (Les & Crawford 1999). (Named for Elias
Landolt, of Geobotanisches Institüt ETH, Zürich, Switzerland, a student of Lemnaceae for more
than 45 years, and the recent contributor of Lemnaceae for Flora of North America)
REFERENCES: Saeger 1934; Crawford & Landolt 1993; Jordan et al. 1996; Les & Crawford 1999.
Landoltia punctata (G. Mey.) Les & D.J. Crawford, (punctate, dotted), DOTTED DUCKMEAT, LARGE
DUCKWEED. Closely resembling some Lemna species in size and shape but easily distinguished
by the presence of more than one root; fronds floating on water surface, solitary or in clusters of
a few, oblong-ovate to somewhat elliptic-reniform, flat or gibbous, 1.5–5(–8) mm long, usually
ca. 1–3 mm wide, 1.5–2 times longer than wide, with (3–)5–7 inconspicuous veins, the upper surface
dark lustrous green, usually without a conspicuous red dot, often with small papillae, the
lower surface usually reddish purple; roots usually 2–7(–12) per frond, to 7 cm long, all penetrating
a small membranous scale (= prophyllum) enveloping base of frond; turions absent;
vegetative reproductive pouches 2 per frond, these lateral near frond base; flowers 1(–2) per
frond, but plants seldom flowering. Quiet waters; much less collected in East TX than Spirodela
polyrhiza; Jasper (BRIT), Brazos, Gregg, Orange, Rusk, Shelby (Landolt 1986), Madison, Sabine
(Turner et al. 2003 as Spirodela punctata), and Liberty (Brown et al. 2002) cos. in the