Flora of the Southeastern United States
2022 Edition

Colors

Data mode

Account

Login
Sign up

Click the number at the start of a key lead to highlight both that lead and its corresponding lead. Click again to show only the two highlighted leads. Click a third time to return to the full key with the selected leads still highlighted.

Key to Aristida

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; [of wet pinelands of FL]
..2 Leaves 0.5-1.5 mm wide and almost always tightly involute; [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).
............ 7 Lateral awns 5-13 mm long, spreading
............ 7 Lateral awns 1-4 mm long, erect
............ ..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 curved (or contorted at the base).
............ ....9 Lateral awns < ½ as long as the central awn.
............ ......10 Inflorescences 15-25 cm wide; loosely cespitose perennial, unbranched upward
............ ......10 Inflorescences 1-6 cm wide; annuals, much branched above the base.
............ ........11 Awns flattened at the base
............ ........11 Awns terete at the base.
............ ..........12 Lemmas 8-22 mm long; central awn curved ca. 180 degrees at the base
............ ..........12 Lemmas 2.5-10 mm long; central awn curved ca. 90 degrees at the base.
............ ............ 13 Central awn (8-) 12-27 mm long; lateral awns (1-) 6-18 mm long
............ ............ 13 Central awn mostly 1-10 (-14) mm long; lateral awns 0-5 (-8) mm long
............ ....9 Lateral awns > ½ as long as the central awn.
............ ............ ..14 Sheaths lanose or floccose (the hairs kinked and intertwined); nodes of the panicle axis with tufts of lanose or floccose hairs
............ ............ ..14 Sheaths glabrous to pilose (the hairs straight and usually appressed, not intertwined); nodes of the panicle axis glabrous or pilose.
............ ............ ....15 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.
............ ............ ......16 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
............ ............ ......16 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
............ ............ ....15 Awn column or lemma beak absent or < 7 mm long; lemma body not separated from the awns by an articulation zone.
............ ............ ........17 Main lower branches of the panicle divergent from the culm and with pulvini
............ ............ ........17 Main lower branches of the panicle (or pedicels in racemose species) ascending to appressed and lacking pulvini.
............ ............ ..........18 Spikelets borne singly at each node of the main axis, the inflorescence thus a spike or raceme
............ ............ ..........18 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).
............ ............ ............ 19 First glume 1/3-¾ the length of the second glume
............ ............ ............ 19 First glume > ¾ the length of the second glume.
............ ............ ............ ..20 Central awn 15-40 mm long; first glume prominently 2-keeled, (8-) 9-14 mm long when mature
............ ............ ............ ..20 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.
............ ............ ............ ....21 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].
............ ............ ............ ......22 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
............ ............ ............ ......22 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
............ ............ ............ ....21 Central awn < 1.5× as thick as the lateral awns, erect to divergent; first glume 1-keeled (rarely weakly 2-keeled); [dry habitats].
............ ............ ............ ........23 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
............ ............ ............ ........23 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.
............ ............ ............ ..........24 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
............ ............ ............ ..........24 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