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

1112 POTAMOGETONACEAE/POTAMOGETON
1. Submersed leaves either � 2.5 mm wide OR � 20 times longer than wide, linear-lanceolate to
lanceolate, oblanceolate, oblong, or elliptic; floating leaves, if present, with blades usually � 40
mm long.
4. Leaves all submersed, sessile, weakly to strongly clasping at base; leaf margins finely toothed
(visible to the naked eye), often undulate-crisped (= � ruffled) ____________________________ P. crispus
4. Leaves usually not all submersed, floating leaves commonly present by flowering time, occasionally
absent; submersed leaves sessile or petiolate, not clasping the stem, with leaf margins
entire or nearly so, not undulate-crisped or sometimes somewhat undulate-crisped.
5. Petioles of floating leaves 2–9 cm long, usually shorter than the blades; submersed leaves
acute to abruptly acuminate or mucronate, usually persistent, sessile or tapering to petioles
to 4 cm long; species known in East TX mainly from w margin of area (but widely
scattered in TX, particularly the Edwards Plateau) __________________________________ P. illinoensis
5. Petioles of floating leaves 4–20 cm long, usually longer than the blades; submersed leaves
acute to blunt-tipped, sometimes disintegrating by fruiting time (P. nodosus), sessile or tapering
to petioles to 3.5(–4.5) cm long (P. pulcher) OR petioles often much longer, (2–)3–13
cm long (P. nodosus); including species widespread in East TX.
6. Floating leaf blades cuneate or rounded at base; submersed leaf blades not arcuate, flat
marginally, tapering gradually to a petiole (2–)3–13 cm long; stems not spotted; mature
fruits usually reddish, 4.3 mm or less long; species widespread and common in East TX
________________________________________________________________________ P. nodosus
6. Floating leaf blades usually cordate, rarely rounded at base; submersed leaf blades often
arcuate (= curved), crispate marginally; tapering rather abruptly to a sessile base or
short petiole to 3.5(–4.5) cm long; stems usually conspicuously black-spotted; mature
fruits light-brown to olive-green, 5–6.5 mm long; species less common in East TX ________ P. pulcher
Potamogeton crispus L., (crimped), CURLY MUCKWEED, CURLY PONDWEED, CURLED PONDWEED.
Leaves all submersed, sessile, with finely toothed and often undulate-crisped (= � ruffled) margins,
linear-oblong to linear-oblanceolate, oblong, or oblanceolate, 3–10 cm long, 3–10(–15) mm
wide; turions common. Widely scattered localities in TX including Burnet, Dallas, Hays, Travis,
Wichita (BRIT), Grayson, Randall (Ogden 1966), and Hemphill (Turner et al. 2003) cos.; s Canada
and throughout most of the U.S. Spring–Jun. Native of Eurasia (Wehrmeister & Stuckey 1992).
This species, which was apparently introduced into North America about 1840, has subsequently
spread throughout much of the continent (Stuckey 1979; Haynes & Hellquist 2000b). It
is the only species of PONDWEED in North America with toothed leaves (Haynes & Hellquist
2000b). Potamogeton crispus is unusual in completing its fruiting in early summer, with the
plants then decaying. Only fruits and turions survive the summer; the turions germinate in late
summer or fall and the resulting small plants overwinter—even under the ice in northern states
such as Ohio (Stuckey et al. 1978; Wehrmeister & Stuckey 1992; Haynes & Hellquist 2000b).
This species is typically found in highly alkaline waters (Hellquist 1980), possibly explaining
its distribution only on the w margin of East TX where soils are alkaline. It is considered to be
the “most distinctive species within the genus” (Wiegleb & Kaplan 1998). I
Potamogeton diversifolius Raf., (diverse-leaved), WATER-THREAD PONDWEED, WATER-THREAD.
Submersed leaves sessile, linear, 1–8 cm long, 0.3–1.5 mm wide; floating leaves sometimes absent,
if present, the blades 5–40 mm long, 3–20 mm wide, the petioles mostly 5–40 mm long;
turions absent. Widespread in e 1/2 of TX, scattered further w; throughout much of the e U.S.,
scattered further w. May–Sep. [P. capillaceus Poir., in part; P. diversifolius var. trichophyllus in
sense of Correll and Johnston 1970—this is actually a synonym of P. bicupulatus Fernald, a species
of the ne U.S.] While Correll and Johnston (1970) recognized two varieties of this species,
we are following the recent treatment in Flora of North America (Haynes & Hellquist 2000b) in
treating this species as a variable entity without subdivisions. According to Haynes and
Hellquist (2000b), this is likely the most common Potamogeton in the se U.S.