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Panicum
See list of 9 species in this genusRecent phylogenetic research showed convincingly that a broadly defined Panicum is artificial (Aliscioni et al. 2003, Zuloaga et al. 2006). Not only are Dichanthelium and Coleataenia well-supported segregates, but also P. verrucosum will need to be segregated into a separate genus. References: Darbyshire and Cayouette (1995), Freckmann and Lelong (2003b).
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1a. Upper glumes and lower lemmas distinctly verrucose with hemispherical protruberences, faintly veined [Fig. 248]
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1b. Upper glumes and lower lemmas not verrucose, with distinct veins
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2a. Plants perennial, from rhizomes
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3a. Panicle open, with ascending to spreading branches; plants sometimes pubescent on the leaf sheaths and/or blades
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3b. Panicle contracted, with strictly ascending to appressed branches [Fig. 246]; plants glabrous throughout
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2b. Plants annual, from fibrous roots
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4a. Lower glume truncate to subacute at the apex, 20–33% as long as the upper glume; sheaths ± compressed, glabrous; plants often somewhat spongy near base
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4b. Lower glume acute to acuminate at the apex, 33–75% as long as the upper glume; sheaths ± terete, pubescent; plants not spongy near base
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5a. Spikelets 4–6 mm long; upper (i.e., fertile) florets 2–2.5 mm wide; panicles dense, often arching or nodding at maturity
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5b. Spikelets 1.4–4 mm long; upper florets 0.4–0.9 mm wide; panicles open, upright
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6a. Panicles with ascending to spreading-ascending branches, more than 2 times as tall as wide, 1–6 cm wide, with glabrous axillary pulvini; anthers 1.2–1.5 mm long
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6b. Panicles with spreading-ascending to spreading branches, less than 2 times as tall as wide, 4–24 cm wide (narrower in depauperate individuals), with pubescent or glabrous axillary pulvini; anthers 0.7–1.2 mm long
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7a. Panicle usually more than 50% of the total plant height [Fig. 247], often breaking at the base of the peduncle and wind-dispersed; spikelets (1.9–) 2.3–4 mm long; upper floret usually light brown-yellow to light brown (rarely dark brown), 0.45–0.60 times as long as the entire spikelet
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7b. Panicle usually less than 50% of the total plant height, not breaking at the base of the peduncle; spikelets 1.4–2.4 mm long; upper floret dark brown at maturity (light brown in P. philadelphicum ssp. gattingeri), 0.54–0.79 times as long as the entire spikelet
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8a. Spikelets 1.8–2.4 at maturity; anthers 0.9–1.2 mm long; upper florets 1.20–1.55 ×0.60–0.85 mm at maturity; uppermost leaf (i.e., the one immediately below the inflorescence) with a blade length to sheath length ratio of 0.8–2.6
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8b. Spikelets 1.4–1.8 (–2) mm long at maturity; anthers 0.7–0.9 mm long; upper florets 0.75–1.3 ×0.42–0.65 mm at maturity; uppermost leaf with a blade length to sheath length ratio of 2–3
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Each photo represents one species in this genus.