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

1114 POTAMOGETONACEAE/STUCKENIA
subsp. pusillus, BABY PONDWEED, SMALL PONDWEED. Widespread in TX; this is the common subspecies
in East TX; nearly throughout s Canada and the U.S.
subsp. tenuissimus (Mert. & W.D.J. Koch) R.R. Haynes & Hellq., (extremely fine, thin). Bowie Co.
(Ogden 1966; Turner et al. 2003 as P. berchtoldii) in the extreme ne part of East TX; widespread
in s Canada and much of the U.S. [P. berchtoldii Fieber, P. berchtoldii var. tenuissimus (Mert. &
W.D.J. Koch) Fernald, P. pusillus var. tenuissimus Mert. & W.D.J. Koch] While known from only
one collection in TX, according to Haynes and Hellquist (2000b), this “is the most common linear-leaved
taxon of the family in temperate North America.” No county distribution map is
provided for the single locality of this variety. While not officially designated as such (e.g.,
TOES 1993; Carr 2002d; Poole et al. 2002), given its limited distribution in the state, we consider
this subspecies to be of conservation concern in TX. �
Potamogeton amplifolius Tuck., (large-leaved), BROAD-LEAF PONDWEED, LARGE-LEAF PONDWEED,
occurs just north of the Red River in OK and, according to Haynes and Hellquist (2000b), is expected
in TX; it is widespread in s Canada and much of the U.S., particularly the e part. The
submersed leaves of this species are “larger than those of most other species of Potamogeton, are
arcuate, and have more veins than do any other species.” It would key to P. pulcher in the key
above, but can be distinguished as follows (from Haynes & Hellquist 2000b):
1. Submersed leaf blades ovate, with 19–49 veins; floating leaf blades with 27–49 veins __________ P. amplifolius
1. Submersed leaf blades linear-lanceolate to lanceolate, with 7–19 veins; floating leaf blades with
15–21(–29) veins ___________________________________________________________________ P. pulcher
STUCKENIA Börner FALSE PONDWEED
AA � cosmopolitan genus of ca. 6 species previously treated as Potamogeton subgenus
Coleogeton (Haynes & Hellquist 2000b). While the taxa now treated in Stuckenia have long
been included in Potamogeton, according to Haynes and Hellquist (2000b), “Recent molecular
evidence (D.H. Les, unpublished), combined with existing morphologic evidence, indicates that
Potamogeton in the broad sense actually represents two separate lineages. We recognize those
lineages at the generic level, Potamogeton in the strict sense and Stuckenia.” While we are recognizing
the genus Stuckenia for East TX, it should be noted that Wiegleb and Kaplan (1998)
disagree, indicating that “the reasons for separating this group from the genus Potamogeton are
not regarded as convincing.” (Derivation unknown, not given by original author)
REFERENCES: Börner 1912; St. John 1916; Ogden 1966; Haynes 1968, 1986; Larson & Barker 1986;
Les & Haynes 1996; Holub 1997; Haynes et al. 1998e.
Stuckenia pectinata (L.) Börner, (comb-like), FENNEL-LEAF PONDWEED, SAGO PONDWEED, SAGO,
SAGO FALSE PONDWEED. Rhizomatous, aquatic, perennial herb, often growing in large masses;
rhizomes sometimes with tubers; stems ca. 1 mm in diam., much-branched above, 0.3–0.75 m
long; leaves all submersed, alternate, sessile, filiform to narrowly linear, 3–9.2 cm long, 0.2–1
mm wide, marginally entire; stipules fused with the leaf base for 10–30 mm and forming a
sheath enfolding the stem (leaf thus seemingly arising from apex of sheath), the free portion of
the stipules less than half as long as fused portion (i.e., stipules adnate for 2/3 or more of their
length); turions absent; peduncles axillary, 3–25 cm long, flexuous, the inflorescences thus submersed;
inflorescence a capitate or cylindrical, often interrupted spike with 2–5(–7) whorls of
flowers, in fruit to 5 cm long; fruits 2.5–4 mm long, apiculate. Travis Co. (Ogden 1966; Turner et
al. 2003) on w margin of East TX; widely scattered in TX; widespread in s Canada and throughout
the U.S., except parts of the se. May–Oct. [Coleogeton pectinatus (L.) Les & R.R. Haynes,
Potamogeton pectinatus L.] The fruits and vegetative parts (e.g., tubers) are very important foods
for wildlife such as ducks (Moore 1913; Correll & Correll 1972). This species is known to reproduce
vegetatively by its tubers (Haynes & Hellquist 2000b). It is typically found in highly alkaline