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

UROCHLOA/POACEAE 1091
AA C4 genus of ca. 100 species (including most species previously treated in Brachiaria) of
tropical, subtropical, and warm areas of the world, with greatest diversity in the Old World
Tropics (Crins 1991; Wipff & Thompson 2003). Some Urochloa species resemble either Panicum
or Paspalum and at times have been placed in those genera. East TX species have in the
past been treated in Panicum or more commonly in Brachiaria (e.g., Correll & Johnston 1970;
Gould 1975b; Hatch et al. 1990; Kartesz 1994). However, characters previously used to separate
Brachiaria and Urochloa are unreliable (Webster 1988), and we are following most recent authors
(e.g., Webster 1988; Morrone & Zuloaga 1992; Jones et al. 1997; Kartesz 1999; Wipff &
Thompson 2003) in treating the species in Urochloa. Brachiaria, as presently considered in the
narrow sense (only ca. 1–3 species), is a small, originally Old World genus now more widely introduced
(Morrone & Zuloaga 1992); it is not known from East TX (Fox et al. 1996). The two
genera can be distinguished by the fertile (upper) florets (roughened-rugose in Urochloa,
smooth and shiny in Brachiaria). Urochloa maxima (Jacq.) R.D. Webster (GUINEA GRASS), native
to Africa, is “of immense economic importance in the tropics as a forage crop” (Crins 1991).
Other species are used for fodder or as pasture grasses (Watson & Dallwitz 1992). (Presumably
from Greek: ouros, tail, and chloa, grass, in reference to the abruptly awned lemmas of some species—Wipff
& Thompson 2003) (subfamily Panicoideae, tribe Paniceae)
REFERENCES: Chase 1920a; Webster 1988; Webster et al. 1989; Crins 1991; Morrone & Zuloaga
1992, 1993; Wipff et al. 1993; Fox et al. 1996; Wipff & Thompson 2003.
1. Spikelets conspicuously (at a quick glance) arranged on one side of each flattened main inflorescence
branch, the main branches not rebranched; plants sometimes superficially resembling
Paspalum.
2. Plants perennial, large, 90–200(–300) cm tall; nodes villous; inflorescences 5–10 cm wide; species
known in East TX only from Jefferson Co. in se corner of the area ______________________ U. mutica
2. Plants annual, smaller, to 60(–100) cm tall; nodes glabrous or with sparse pubescence; inflorescences
2–5 cm wide; species widespread in East TX.
3. Spikelets small, 1.8–2.2 mm long, mostly in unequally pedicelled pairs except near branch
tips; lower glume clearly much less than 1 mm long (0.2–0.5 mm); inflorescence branches
3(–4) cm or less long; culms ca. 35 cm or less tall _____________________________________ U. reptans
3. Spikelets relatively larger, 3.5–4.5(–5) mm long, solitary at mid-branch; lower glume 1.2–1.8
mm long; inflorescence branches 3–8 cm long; culms 30–60(–100) cm tall ____________ U. platyphylla
1. Spikelets not conspicuously arranged on one side of each flattened inflorescence branch, the main
inflorescence branches sometimes rebranched; plants sometimes superficially resembling Panicum.
4. Branches at lowest node of inflorescence in whorls; inflorescence an open panicle, the primary
branches with secondary and tertiary branches; plants perennial ____________________ U. maxima
4. Branches at lowest node of inflorescence not in whorls; inflorescence usually with spikelike
branches, these unbranched or sometimes with secondary branches; plants annual or
perennial.
5. Spikelets 1.8–2.2 mm long; lower glume 0.5 mm or less long ___________________________ U. reptans
5. Spikelets usually 2.4–6 mm long; lower glume (0.6–)1–ca. 4 mm long.
6. Lower glume ca. 2/3–3/4 as long as spikelet, ca. (2.3–)3–4 mm long; spikelets (3–)3.5–6
mm long; upper glume densely long-hairy OR not so.
7. Spikelets (3–)3.5–4.5 mm long; upper glume densely long-hairy; inflorescences 2–7
cm long _____________________________________________________________ U. ciliatissima
7. Spikelets 5–6 mm long; upper glume glabrous or with scattered hairs, not densely
long-hairy; inflorescences usually 7–25 cm long _________________________________ U. texana
6. Lower glume 1/4–1/2 as long as spikelet, 1.5 mm or less long; spikelets 2.4–3.5 mm
long; upper glume glabrous.
8. Upper glume with distinct cross veins; upper glume and lemma of lower floret
glabrous; lemma of lower floret with 7 veins ______________________________________ U. fusca