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

1148 ZANNICHELLIACEAE/ZANNICHELLIA
var. stricta. Plants “taller, wider leaved, smoother, broader scaped, larger bracted” (Kral 2000a)
than var. obscura. Acid swamps, deep wet bogs, wet savannahs, and wet sands, but mostly on
peat-muck substrates, in wetter habitats than var. obscura; included based on mapped location
(county unspecified) in extreme se part of the Pineywoods in Kral (2000a); se U.S. from SC s to
FL w to TX. Flowers opening later in morning, closing early afternoon; summer–fall.
Xyris torta Sm., (twisted), TWISTED YELLOW-EYED-GRASS, SLENDER YELLOW-EYED-GRASS. Perennial,
solitary or in tufts of a few individuals, bulbose-based; leaves 20–50 cm long, 2–5 mm
wide, twisted; scapes 15–80(–100) cm long; spikes 8–25 mm long; sepal keels ciliate. Wet soils,
bogs, stream banks and lake shores, wet sandy swales, and acid sandy swamps; widespread in
Pineywoods and Post Oak Savannah; widespread in the e U.S. from NH s to GA w to MN, OK,
and TX. Flowers opening in the morning; Jun–Jul. According to Kral (2000a), “Xyris torta is the
widest-ranging of all North American xyrids and the most expressive ecologically; thus it is
not surprising that it varies so much morphologically. It is often confused in the older literature
with X. caroliniana. Xyris torta is the type species for the genus.” See further discussion under
X. caroliniana.
ZANNICHELLIACEAE Dumort
HORNED-PONDWEED FAMILY
AA very small (10–12 species in 4 genera—Haynes & Hellquist 2000c) but nearly cosmopolitan
family of submersed aquatic herbs. It is one of relatively few families that exhibit
hydrophily—water-mediated pollination; in Zannichellia pollination actually occurs underwater
(hypohydrophily) in contrast to some cases of hydrophily in which pollination occurs at
the water surface (epihydrophily; e.g., Vallisneria in the Hydrocharitaceae or Ruppia in the
Ruppiaceae) (Guo et al. 1990; Philbrick 1991, 1993). The family has been treated by some authorities
in the Zosteraceae (EEL-GRASS family) (Tyrl et al. 1994) or as part of the Potamogetonaceae
(APG 1998; APG II 2003). According to some research, it appears to occupy an isolated position
at the base of a clade leading to these two families (Les et al. 1993). However, based on molecular
studies, the Zannichelliaceae is apparently most closely related to Potamogetonaceae (Les &
Haynes 1995), with the two being closely related sister groups (Haynes et al. 1998d). While recognizing
the close relationship of the two families, we are following most recent treatments (e.g.,
Haynes et al. 1998d; Haynes & Hellquist 2000c; Reveal & Pires 2002) in maintaining
Zannichelliaceae as a distinct family; whether to lump or split in this case seems arbitrary—
therefore, not changing traditional circumscription seems the most prudent approach. (subclass
Alismatidae—Cronquist; order Alismatales—APG II)
FAMILY RECOGNITION IN THE FIELD: the single East TX species is a submersed aquatic herb with
opposite or apparently whorled, entire, almost thread-like leaves and small, curved, stalked
fruits.
REFERENCES: Morong 1893; Campbell 1897; Taylor 1909a; Tomlinson & Posluszny 1976;
Dahlgren et al. 1985; Haynes & Holm-Nielsen 1987; Haynes et al. 1998d; Haynes & Hellquist
2000c.
ZANNICHELLIA L. HORNED-PONDWEED
AA nearly cosmopolitan genus of 1–ca. 5 species (Mabberley 1997; Haynes & Hellquist 2000c);
pollination occurs underwater. (Named for Gian Girolamo Zannichelli, 1662–1729, a Venetian
botanist and apothecary—Haynes & Hellquist 2000c)
REFERENCES: Reese 1967; Van Vierssen 1982a, 1982b, 1982c; Guo et al. 1990.
Zannichellia palustris L., (marsh-loving), COMMON POOLMAT, HORNED-PONDWEED. Monoecious,
submersed, aquatic herb; stems much-branched; leaves opposite but sometimes appearing