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

988 POACEAE/OPLISMENUS
REFERENCES: Hitchcock 1925; Parodi 1947; Brown 1952; Thomasson 1978; Barkworth 1990, 1993,
ined.; Tucker 1990; Valdés-Reyna & Barkworth 1994; Jacobs et al. 2000; Barkworth & Torres 2001.
Nassella leucotricha (Trin. & Rupr.) Pohl, (white-haired), WINTER GRASS, TEXAS WINTER GRASS,
SPEAR GRASS, TEXAS NEEDLE GRASS, TEXAS TUSSOCK GRASS. Perennial, tufted, 25–100(–120) cm tall,
green from late fall to summer; ligule variable, absent or a membrane to 1 mm long; leaf blades
3.6 mm or less wide; panicles terminal, open; axillary cleistogamous florets produced in lower
sheaths; spikelets 1-flowered, disarticulating above the glumes; glumes acuminate, (12–)14–18
(–21) mm long; lemma 9–13 mm long, indurate, light brown, with overlapping margins; lemma
base and rachilla together forming a sharp-pointed bearded callus 1.5–4.5 mm long; lemma
apex with smooth white neck (crown) ca. 0.6–1(–2) mm long, the crown often flaring from its
base; lemma awn very long (4–10 cm), geniculate, twisted, with a ring of whitish hairs around
base; caryopsis permanently enclosed within the lemma. Prairies, disturbed sites; throughout
TX; AR, LA, OK, SC, and TX. Apr–May. This species was a minor component of the original
prairie and increases under disturbance. [Stipa leucotricha Trin. & Rupr.] The callus is so sharppointed
that it will easily stick into clothing or skin; Correll and Johnston (1970) indicated that
when thrown they are “… therefore, of considerable recreational value to boys.” Unfortunately,
they can also cause wounds to the mouth or other body parts of animals (Lipscomb & Diggs
1998). The dispersal unit of this species (sharp callus derived in part from rachilla and a fertile
floret with obvious awn) and the dispersal unit of Heteropogon melanocarpus, SWEET TANGLE-
HEAD (sharp callus derived in part from inflorescence axis, glumes, vestigial sterile floret, and
fertile floret with obvious awn), look and function remarkably alike yet are structurally quite
different. This is a good example of convergent evolution.
OPLISMENUS P. Beauv. BASKET GRASS, MOUNTAIN GRASS
AA small C3 genus of about 5 variable and very closely related species of the tropics and warm
areas. There is, however, considerable disagreement on the exact number of species, with some
authorities recognizing 9 (Scholz 1981) or even more (10–15 species—Pohl & Davidse 1994a).
Oplismenus hirtellus cultivar ‘Variegatus’ is a cultivated greenhouse hanging-basket plant sometimes
sold under the misnomer Panicum variegatum (Wipff 2003h). Several are significant weeds
(Watson & Dallwitz 1992). Davidse (1987a) indicated that most species have sticky secretions on
the awns, which serve as a mechanism of animal dispersal. Clayton and Renvoize (1986) noted
that this “is an unusual means of fruit dispersal in the grasses,” and the spikelets, which adhere to
clothing, have been referred to as “stick-tights” (Peterson et al. 1999). (Greek: hoplismos, a weapon,
or hoplismenos, armed, referring to the awns) (subfamily Panicoideae, tribe Paniceae)
REFERENCES: Hitchcock 1920a; Kerguélen 1976; Smith 1976; Davey & Clayton 1978; Scholz 1981;
Crins 1991; Peterson et al. 1999; Wipff 2003h.
Oplismenus hirtellus (L.) P. Beauv. subsp. setarius (Lam.) Mez ex Ekman, (sp.: rather hairy; subsp.:
containing bristles), BASKET GRASS, LONG-LEAF BASKET GRASS. Perennial with culms creeping
and rooting at the nodes; nodes usually pubescent; culm axis and leaf sheaths glabrous or with
a few scattered hairs; ligule a ciliate membrane; leaf blades 1.5–7.3 cm long, (2–)5–15(–20) mm
wide, widely spreading to reflexed; inflorescence with 3–5(–7) widely spaced, very short, spikelike
branches ca. 1–6 mm long, with spikelets sessile or nearly so, in 2 rows on 1 side of each
branch; spikelets 2.2–3(–3.3) mm long, 2-flowered, the lower floret sterile, the upper floret perfect;
disarticulation usually below glumes (and occasionally below fertile floret); glumes
subequal, awned; awn of lower glume 4–10 mm long, much longer than awn of upper glume
(ca. 1–4 mm long); lemma of sterile floret with awn 1.2 mm or less long; lemma of fertile floret
indurate, the margins virtually enclosing the palea. Shaded moist areas; widespread in e 1/3 of
TX; most of se U.S. from MD s to FL w to OK, and TX. Summer–Oct. Native to New World tropics
and subtropics. [O. compositus (L.) Beauv. var. setarius (Lam.) F.M. Bailey, O. setarius (Lam.)