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

1078 POACEAE/THEMEDA
THEMEDA Forssk. KANGAROO GRASS, CHRISTMAS GRASS
AAn Old World tropical and subtropical genus of ca. 18 species (Barkworth 2003m), including
some of the principal cover grasses in tropical fire-maintained grasslands. Some are used as ornamentals
and others as forage; several are significant weed species (Watson & Dallwitz 1999).
Like all members of the Andropogoneae, Themeda is characterized by C4 photosynthesis
(Watson & Dallwitz 1999; Kellogg 2000a). (Arabic: thaemed, a depression where water collects
after rain and later evaporates, in reference to the habitat of some species—Barkworth 2003m)
(subfamily Panicoideae, tribe Andropogoneae)
REFERENCES: Chippindall 1955; Gibbs Russell et al. 1991; Towne & Barnard 2000; Barkworth
2003m.
Themeda triandra Forssk., (with three stamens), KANGAROO GRASS, ROOIGRAS. Tufted rhizomatous
perennial to 90(–150+) cm tall; leaf sheaths compressed, often with reddish coloration; ligule a
notched membrane, sometimes ciliate; leaf blades abruptly or gradually pointed; inflorescences
� triangular clusters (of 1–several short, almost spikelet-like racemes) from the upper nodes
(many clusters per culm), often drooping, typically (1–)1.5–2 cm long (not counting awns), each
cluster subtended by a reddish spathe-like sheath 1.5–7 cm long; each cluster subunit (raceme)
with 2 pairs of sterile or staminate sessile spikelets at base, forming what appears to be a loose
involucre below the rest of the raceme, these involucral spikelets 6–15 mm long, awnless; rest of
the raceme consisting of 1–4 smaller pairs of one sessile and one pedicellate spikelet, or sometimes
only 3 spikelets with 1 sessile and fertile and 2 pedicellate and sterile or staminate; sessile,
fertile spikelets 5–14 mm long, with a sharply pointed callus with brown hairs, composed of 2
florets, the lower reduced and sterile, the upper floret fertile, with lemma bearing a stout, bent,
and twisted awn 3–7+ cm long, the palea absent; stamens 3; pedicellate spikelets similar to involucral
spikelets, unawned. “Grass near house, recent invader” (from collector’s label); Travis Co.
(Wendt 6988, Nov 1997—TEX, previously Blackland Prairie site near Pflugerville); in the U.S. apparently
known only from TX. Fall. [T. australis (R. Br.) Stapf] Native of the Old World. Themeda
triandra is an exceedingly variable, taxonomically complex species divided by some authorities
into numerous infraspecific taxa (e.g., Chippindall 1955). Because of the lack of comparative
material or detailed treatments of the entire group, we are tentatively treating the species broadly
without varieties or subspecies, to include T. australis (which is recognized by some authorities as
a separate species). Themeda triandra is currently known from only a single collection in East
TX, and thus appears to be a relatively recent arrival. As with many introduced species, its eventual
abundance or impact is difficult to predict (i.e., will it become invasive?). The species is, however,
widely dominant in parts of its native range and in some areas is considered an important
native pasture grass (Watson & Dallwitz 1999). It can vegetatively resemble Heteropogon contortus,
but that species has an undivided ligule and blunt leaf blades (Gibbs Russell et al. 1991). I
TRACHYPOGON Nees CRINKLE-AWN GRASS
AA genus of ca. 6 species of tropical and subtropical America and Africa (Dávila 1994; Wipff
& Jones 1998). According to Allred (2003f), “Estimates of the number of species included range
from 1 to 10. One species, Trachypogon secundus, grows in and is native to the [North American]
Flora region, but some taxonomists (e.g., Dávila 1994) include it in T. plumosus (Humb. & Bonpl.
ex Willd.) Nees and others (e.g., Judziewicz 1990b) include it, T. plumosus, and various other
taxa in T. spicatus (L.f.) Kuntze.” We are following Allred (2003f) in using the traditional treatment
and nomenclature for North American plants because of the lack of evidence supporting
the various other treatments. Like all members of the Andropogoneae, Trachypogon is characterized
by C4 photosynthesis (Watson & Dallwitz 1999; Kellogg 2000a). (Greek: trachus, rough,
and pogon, beard, in reference to the plumose awn of the lemma of fertile floret) (subfamily
Panicoideae, tribe Andropogoneae)
REFERENCES: Judziewicz 1990b; Dávila 1994; Wipff & Jones 1998; Allred 2003f.