Nassella trichotoma |
Poaceae subfam. pooideae |
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serrated tussock, serrated tussockgrass, yass tussockgrass |
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Habit | Plants perennial; cespitose, not rhizomatous. | Plants annual or perennial; sometimes matlike, sometimes cespitose, sometimes stoloniferous, sometimes rhizomatous. | ||||||||||||||||||||||||||||||||||||
Culms | 20-60 cm tall, about 1 mm thick, erect, internodes glabrous; nodes 2-4, pubescent. |
usually hollow, sometimes solid. |
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Sheaths | glabrous, smooth; collars glabrous, without tufts of hair at the sides; ligules 0.5-2.5 mm, glabrous, obtuse; blades 15-45 cm long, 0.2-0.6 mm wide, convolute, stiff, scabridulous. |
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Leaves | distichous; sheaths usually open to the base, varying to closed for nearly their full length; auricles present or absent; abaxial ligules absent; adaxial ligules scarious or membranous, sometimes puberulent or scabridulous, usually not ciliate, cilia sometimes shorter than the base; pseudopetioles rarely present; blades usually linear, sometimes broadly so, venation parallel; cross sections non-Kranz, mesophyll nonradiate, adaxial palisade layer absent, fusoid and arm cells usually absent; midribs usually simple; adaxial bulliform cells present; stomates with parallel-sided subsidiary cells; epidermes usually lacking bicellular microhairs, sometimes with unicellular microhairs, papillae usually absent, when present, rarely more than 1 per cell. |
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Panicles | 8-25 cm, open, lax, sparse; branches 2-6 cm, with 1-8 spikelets; pedicels 3-12 mm. |
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Inflorescences | usually terminal, panicles, spikes, or racemes, usually ebracteate; disarticulation usually below the florets, sometimes below the glumes, at the rachis nodes, or at the inflorescence bases. |
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Spikelets | usually bisexual, infrequently unisexual or mixed, usually laterally compressed or not compressed, occasionally dorsally compressed, with 1-30 sexual florets, distal floret(s) often reduced, infrequently spikelets with 1-2 reduced or staminate basal florets and a single terminal sexual floret. |
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Glumes | subequal, 4-10 mm long, 0.9-1.2 mm wide, narrowly lanceolate, scabridulous, apices aristate; florets 1.5-2.5 mm long, 0.7-0.9 mm wide, terete, widest near the top; calluses 0.1-0.3 mm, acute, strigose, hairs reaching to midlength on the lemmas; lemmas strongly tuberculate, particularly distally, mostly glabrous, narrowing abruptly to the crown, midveins pubescent proximally; crowns about 0.5 mm long, about 0.2 mm wide, straight-sided, rims entire or irregularly lacerate, glabrous; awns 15-35 mm, eccentric, straight to twice-geniculate; anthers 3, 1-1.5 mm. |
usually 2, upper or lower glumes sometimes absent, rarely both glumes absent; lemmas without uncinate hairs, awned or not, awns single, basal to apical; paleas usually well-developed, sometimes reduced or absent; lodicules 2(3), usually lanceolate and broadly membranous distally, rarely truncate and fleshy, usually not veined or obscurely veined, sometimes distinctly veined, sometimes ciliate; anthers (1, 2)3; ovaries glabrous or sometimes hairy distally, sometimes with an apical appendage; haustorial synergids absent; styles (1)2 (-4), bases close together, sometimes fused. |
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Caryopses | about 1.2 mm, oblong, dark brown. |
hila linear, elliptic, ovate, or punctate; endosperm usually hard, sometimes soft or liquid, with or without lipids, starch grains compound or simple; embryos less than 1/2 the length of the caryopses; epiblasts usually present; scutellar cleft usually absent; mesocotyl internode usually absent; embryonic leaf margins overlapping, x = 7, 10. |
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2n | = 36. |
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Nassella trichotoma |
Poaceae subfam. pooideae |
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Distribution |
IL; KY; NC; SC |
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Discussion | Nassella trichotoma is a native of South America, and has been accidentally introduced into the United States. Because it is on the U.S. Department of Agriculture's noxious weed list, all known populations have been eliminated. New populations should be reported to the Department. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
The subfamily Pooideae includes approximately 3300 species, making it the largest subfamily in the Poaceae. It reaches its greatest diversity in cool temperate and boreal regions, extending across the tropics only in high mountains. The circumscription and relationships of tribes within the Pooideae are unsettled (see, for example, Catalan et al. 1997, 2004; Soreng and Davis 1998). In this flora, some previously recognized tribes have been combined with the Poeae. Recognition of some of these as subtribes is well supported; among these is the Hainardieae Greuter (which, at the subtribal level, is called the Parapholiinae Caro). Members of other traditional tribal groupings, such as the Aveneae Dumort., appear to be widely dispersed within the Poeae sensu lato. Further work will probably support the division of the expanded Poeae into additional tribes; there is as yet no clear indication as to what the boundaries of such tribes should be. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 24, p. 177. | FNA vol. 24, p. 57. | ||||||||||||||||||||||||||||||||||||
Parent taxa | Poaceae > subfam. Pooideae > tribe Stipeae > Nassella | Poaceae | ||||||||||||||||||||||||||||||||||||
Sibling taxa | ||||||||||||||||||||||||||||||||||||||
Name authority | (Nees) Hack, ex Arechav. | Benth. | ||||||||||||||||||||||||||||||||||||
Web links |