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

578 CYPERACEAE/CYPERUS
possibly best. However, the following varieties were recognized by Carter and Jones (1997). They
indicated that despite “overlap in virtually every characteristic we examined,” when combinations
of characteristics were used, most specimens could be identified to variety. According to
S.D. Jones (pers. comm.), both varieties occur throughout East TX, but var. retroflexus is by far
the most common. For those wishing to distinguish varieties, the following key from Carter
and Jones (1997) is provided.
1. Fertile floral scales 1.9–3(–3.3) mm long; rachilla wing usually membranaceous throughout; rachilla
usually lacking lateral nerves; longest spikelets 2.2–5.8(–8) mm long; terminal sterile floral scale
of spikelet often much reduced, less than 2/3 the length of fertile floral scales; longest peduncle
less than 2.7(–3.9) cm long; plants diminutive, 3–35(–45) cm tall ____________________________ var. pumilus
1. Fertile floral scales (2.8–)3–3.9 mm long; rachilla wing usually chartaceous beyond clasped achene
angle, border membranaceous; rachilla usually with two lateral nerves, one along each side of
median; longest spikelets 4.9–9(–11.3) mm long; terminal sterile floral scale usually not greatly
reduced, 2/3 or more the length of fertile floral scales; longest peduncle (0.5–)2.4–6.8 cm long;
except for depauperate specimens, plants usually greater than 25(–57) cm tall ______________ var. retroflexus
Cyperus retrorsus Chapm., (twisted or turned backward), PINE-BARREN FLAT SEDGE. Tufted perennial;
culms usually 50(–85) cm or less tall; inflorescences with spikelets in extremely
densely cylindric or subcylindric spikes (so dense that outline of spike is smooth); spikes 6–8
(–10) mm broad by 7–18 mm long, more than 1/4 longer than broad; achenes 1.2–1.7 mm long.
Ditches, roadsides, open woods, usually in sandy soils; Pineywoods and Gulf Prairies and
Marshes w to Cross Timbers and Prairies and e Edwards Plateau; e U.S. from NY s to FL w to MO
and TX. Jun–Oct. While some authorities (e.g., Kartesz 1999) recognize varieties in this species,
because of indistinct boundaries even between species within this complex, we are following
Tucker et al. (2002) in not recognizing infraspecific taxa within C. retrorsus. In addition, some
authorities (e.g., Turner et al. 2003) recognize C. cylindricus, which is here synonymized with C.
retrorsus. [C. cylindricus (Elliott) Britton, C. ovularis (Michx.) Torr. var. cylindricus (Elliott) Torr.,
C. retrorsus var. cylindricus (Elliott) Fernald & Griscom]
Cyperus rotundus L., (round), NUT-GRASS, NUT SEDGE, COCO-GRASS, PURPLE NUT-GRASS, PURPLE
NUT SEDGE, PURPLE FLAT SEDGE. Deeply rhizomatous perennial 7–50 cm tall, forming colonies;
rhizomes at intervals with tuber-like thickenings (allowing survival under extreme conditions);
inflorescences with spikelets in relatively open spikes, each spike with 3–9(–12) spikelets;
spikelets dark red-brown to purplish; achenes 1.4–1.8 mm long. Disturbed areas, waste
places, cultivated fields, lawns; widespread in TX; s U.S. from VA s to FL w to CA. May–Oct. Native
of the Old World? (while most authorities—e.g., Hatch et al. 1990—consider this species
introduced, Tucker et al. 2002 do not). Often a pernicious weed known to adversely affect numerous
crops and sometimes referred to as “the world’s worst weed” (Holm et al. 1977;
Mabberley 1987); it is considered a state noxious weed in AZ, CA, GA, and OK (Kartesz 1999).
However, the tuber-like thickenings are “said to be relished by some game animals, particularly
wild turkey” (Godfrey & Wooten 1979). Tucker et al. (2002) consider the underground stems in
this species and in C. esculentus to be stolons; however, because they are underground, we treat
them as rhizomes. They note that the two somewhat similar species can be distinguished as follows:
C. rotundus with the stolons [rhizomes] indurate, wiry, springy when dried; and C.
esculentus with the stolons [rhizomes] spongy, flexible when dried. � ? I
Cyperus setigerus Torr. & Hook., (bearing bristles), LEAN FLAT SEDGE, BRISTLED UMBRELLA SEDGE.
Perennial usually 50–110 cm tall, with shallow creeping rhizomes, forming small colonies; inflorescences
with spikelets in relatively open spikes; spikelets usually reddish brown; achenes
1.4–1.8 mm long. Stream or pond banks, low areas, ditches, in clay soils; mainly in w part of East
TX (where clay soils predominate); also scattered elsewhere in TX; KS, MO, NM, OK, and TX.
May–Sep. According to Yatskievych (1999), “Cyperus setigerus often produces a pleasant, sweet
odor when crushed or dried.”