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

ANDROPOGON/POACEAE
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colonizing early successional or permanently disturbed sites (Campbell 1982). (Greek: aner
(andr), man, and pogon, beard, referring to the hairy pedicels of the staminate spikelets) (subfamily
Panicoideae, tribe Andropogoneae)
REFERENCES: Gould 1957a, 1967; Campbell 1982, 1983a, 1986; Barnes 1986; Wipff 1996b;
Gustafson et al. 1999; Campbell 2003.
1. Sessile spikelets 7–11 mm long; terminal inflorescence conspicuously exserted beyond bracts,
not woolly in appearance; pedicelled spikelets large, well-developed, similar to sessile spikelets
except awnless ___________________________________________________________________ A. gerardii
1. Sessile spikelets 7 mm or less long; inflorescences either not conspicuously exserted beyond
bracts OR if exserted then appearing woolly; pedicelled spikelets rudimentary, vestigial, or represented
by the pedicel only.
2. Inflorescence with 2 relatively stiff and usually straight branches, the spikelets and hairs usually
so dense that the branch axes are not easily visible; sessile spikelets 5–7 mm long; inflorescences
often conspicuously exserted beyond bracts _______________________________ A. ternarius
2. Inflorescence with 2–5 slender, delicate and flexuous branches, the spikelets and hairs often not
as dense, the branch axes thus often visible, sometimes easily so; sessile spikelets 5 mm long or
less; inflorescences usually not conspicuously exserted OR sometimes exserted in A. gyrans.
3. Upper sheathing bract of inflorescence conspicuously inflated and spathe-like; lemma awns
with a loose spiral twist near base; leaf blades 0.8–5 mm wide (typically ca. 2.5 mm); culms
with tufts of long hairs just below sheathing bract of inflorescence; species rare in East TX ______ A. gyrans
3. Upper sheathing bract of inflorescence not inflated; lemma awns straight or nearly so; leaf
blades 1.7–9.5 mm wide (usually � 3 mm); culms glabrous OR with tufts of long hairs just
below sheathing bract of inflorescence; species extremely widespread and abundant in
East TX.
4. Inflorescences crowded apically, together appearing broom-like; culms with tuft of long
hairs below sheathing bract of inflorescence; leaf sheaths usually scabrous, sometimes
smooth; leaf blades 13–109 cm long; ligule 0.6–2.2 mm long _____________________ A. glomeratus
4. Inflorescences numerous but not clustered apically, not broom-like; culms glabrous below
sheathing bract of inflorescence; leaf sheaths usually smooth, rarely scabrous; leaf
blades 11–52 cm long; ligule 0.2–1 mm long ___________________________________ A. virginicus
Andropogon gerardii Vitman, (for Louis Gérard, 1733–1819, French botanist). Plant to 2 m tall,
essentially glabrous, often glaucous; inflorescences of 2–7 digitately arranged branches, the
branches 4–11 cm long; sessile spikelets usually scabrous, often glaucous; upper lemma of
sessile spikelet awned (sometimes awnless in subsp. hallii); pedicellate spikelets about as large
as sessile, awnless. Aug–Nov. This polyploid species has chromosome numbers of both 2n = 6x =
60 and 2n = 9x = 90; the plants are virtually indistinguishable morphologically (Norrmann et
al. 1997). Hybridization between these two main cytotypes is possible, with the resulting individuals
having a range of chromosome numbers (Norrmann & Keeler 2003). The reproductive
biology of this species was studied by McKone et al. (1998) and was found to be very unusual in
allocating more resources to male reproduction (pollen production) than to female reproduction
(seed production). The following key to subspecies is modified from Sutherland (1986) and
Wipff (1996b).
1. Upper lemma of sessile spikelet with an awn (7.5–)10–25 mm long; rhizomes short or absent,
with internodes usually 2 mm or less in length; anthers usually � 3.8 mm long; ligule 0.4–2.5 mm
long ________________________________________________________________________ subsp. gerardii
1. Upper lemma of sessile spikelet awnless or with an awn to 8(–11) mm long; rhizomes welldeveloped,
creeping, with internodes often exceeding 20 mm in length; anthers usually � 3.8
mm long; ligule (0.9–)3–4.5 mm long _________________________________________________ subsp. hallii