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Key to Aristida

Poaceae

Aristida

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1 Plant a perennial, forming dense tussocks, the leaves primarily basal, usually very numerous, mostly > 3 dm long, either 0.5-1.5 mm wide and almost always tightly involute, or 1-3 mm wide and flat or folded; flowering only in the growing season following fire.
  2 Leaves 1-3 mm wide, flat or folded; plants with thick, conspicuous rhizomes; matured basal sheaths shredding into fibrous, threadlike fibers [of wet pinelands of FL]
  2 Leaves 0.5-1.5 mm wide and almost always tightly involute; plants cespitose, only occasionally with rhizomes; basal sheaths not disintegating into fibers; [collectively more widespread in our area, though almost strictly Coastal Plain, from NC south to s. FL, west to s. MS].
    3 Base of blade and collar (and often the upper sheath) with conspicuous tuft or bearding of woolly to villous pubescence (sometimes deciduous on foliage more than a year old); leaves usually glabrous above the basal 2 cm of the blade; [of s. SC south and west to s. FL and s. MS]
    3 Base of blade, collar, and upper sheath lacking a conspicuous tuft of woolly to villous pubescence; leaves with 2 lines of villous pubescence on either side of the midrib on the lower surface extending nearly or entirely the length of the blade (sometimes deciduous on foliage more than a year old); [of n. SC and NC]
1 Plant an annual or perennial, forming small tufts (or solitary), the leaves primarily cauline, usually few, mostly < 3 dm long (if as long as 3 dm then > 2 mm wide), flat to slightly folded, but not wiry; flowering not strongly triggered by fire.
      4 First glume 3-7 nerved.
        5 Central awn of the lemma (8-) 12-65 (-70) mm long, the lateral awns as long or nearly so
        5 Central awn of the lemma (9-) 12-25 (-30) mm long, the lateral awns 1-4 mm long (or even lacking)
      4 First glume 1-2-nerved.
          6 Central awns spirally coiled at the base (above the awn column), like a corkscrew, ½ to 3 full turns (when dry).
               8 First glume 1/2 to 2/3 as long as the second glume; lemma 6-11 mm long, glabrous to scaberulous
               8 First glume as long as or nearly as long as the second glume; lemma 3-8 mm long, sparsely appressed-pubescent
          6 Central awns straight to sickle-shaped or curved (contorted at the base, but not with multiple twists like a corkscew).
                 9 Lateral awns < ½ as long as the central awn (or virtually obsolete).
                   10 Inflorescences usually widely paniculate, (5-) 15-25 cm wide; loosely cespitose perennial, unbranched upward (or mostly unbranched).
                     11 Lateral awns essentially absent or obsolete; central awns 10-25 mm long, falcate; [FL keys]
                     11 Lateral awns 3-10 mm long, ca. ½ as long as the central awns; central awns 20-25 mm long, straight; [throughout FL]
                   10 Inflorescences spike-like or only thinly paniculate, 1-6 cm wide; annuals, much branched above the base.
                          13 Lemmas 8-22 mm long; central awn curved ca. 180 degrees at the base
                          13 Lemmas 2.5-10 mm long; central awn curved ca. 90 degrees at the base.
                 9 Lateral awns > ½ as long as the central awn.
                                16 Awn column (the connivent awns twisted together) or lemma beak (slender, narrowed, and twisted portion of lemma body below the awns) 7-30 mm long; lemma body (including the beak, if present) separated from the awns (or awn column) by an articulation zone, the awns (or awn column) disarticulating at maturity from the lemma.
                                  17 Panicle spiciform, broadest near the middle, dense, the spikelets overlapping strongly; awns (10-) 20-30 mm long, borne at the summit of a twisted lemma beak 7-30 mm long; culms simple or with very few branches; plants perennial
                                  17 Panicle almost corymbiform, broadest above the middle, open, the spikelets overlapping only slightly; awns 30-40 mm long, not including the 8-15 mm long column formed by the twisting together of the 3 awn bases; culms often much-branched; plants annual
                                16 Awn column or lemma beak absent or < 7 mm long; lemma body not separated from the awns by an articulation zone.
                                       19 Spikelets 2 or more per node of the main axis at most nodes (a few nodes may have single spikelets), often with side branches present as well, the inflorescence thus a panicle (less commonly a raceme).
                                           21 Central awn 15-40 mm long; first glume prominently 2-keeled, (8-) 9-14 mm long when mature
                                           21 Central awn 8-25 mm long; first glume either 1-keeled and 6-14 mm long, or weakly 2-keeled and 5.5-9 (-10) mm long when mature.
                                             22 Central awn about 2× as thick as the lateral awns, divergent to reflexed; first glume 1-keeled or weakly 2-keeled; [moist to wet habitats].
                                               23 Basal internode of the culm 0.3-0.6 mm wide; most nodes of the inflorescence with 1-2 spikelets; all awns spreading, the central spirally twisted basally and often contorted by as much as 180 degrees (best seen in fresh material); central awn 15-20 mm long, lateral awns 11-16 mm long, the ratio of the lateral:central awn length 0.69-0.80; lemma callus beard 0.6-1.0 mm long
                                               23 Basal internode of the culm 0.7-1.2 mm wide; most nodes of the inflorescence with 3 or more spikelets; central awn spreading to slightly deflexed, not spirally twisted basally, the lateral awns ascending to erect (best seen in fresh material); central awn 13-22 mm long, lateral awns 8-15 mm long, the ratio of the lateral:central awn length 0.55-0.69; lemma callus beard 0.2-0.6 mm long
                                             22 Central awn < 1.5× as thick as the lateral awns, erect to divergent; first glume 1-keeled (rarely weakly 2-keeled); [dry habitats].
                                                 24 Culms mostly > 10 dm tall and 3-6 mm in diameter near the base; awns 8-15 mm long; panicle branches > 4 cm long; callus ca. 1.0 mm long
                                                 24 Culms 5-8 (-10) dm tall and 1-4 mm in diameter near the base; awns 12-25 mm long; panicle branches 1-4 cm long; callus 0.4-0.8 mm long.
                                                    25 First glume 1-4 mm longer than the second glume (rarely about equal to it); awns 15-25 mm long, straight or slightly contorted at the base; leaf blades 1-3 mm wide, usually curling
                                                    25 First glume shorter than or about equal to the second glume; awns 12-18 mm long, spirally contorted at the base; leaf blades about 1 mm wide, usually not curling