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Agrostis

When determining the presence of an awn borne from the keel of the lemma, refer to the spikelets near the distal portions of branches. Spikelets from near the base of the branches may show shorter awns that are positioned closer to (or at) the tip of the lemma. Reports  of Agrostis pallens Trin. from MA (e.g., Kartesz 1999, Sorrie and Somers 1999) were based on a specimen of Agrostis stolonifera. Reference: Harvey (2007).

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1a. Palea 2-nerved, 0.6–1.4 mm long, (40–) 50% or more as long as the lemma; plants mostly with rhizomes and/or stolons
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  A. capillaris
  2a. Ligules 0.5–2 mm long, usually wider than long; branches of panicle bearing flowers only in the distal half; horizontal stems (i.e., rhizomes or stolons) up to 5 cm long
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  2b. Ligules 2–6 mm long, usually longer than wide; branches of panicle bearing flowers  in both distal and proximal halves [Fig. 180]; horizontal stems usually longer than 5 cm
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    A. gigantea
    3a. Inflorescence with spreading branches during and after anthesis [Fig. 180],  (8–) 10–25 cm tall, usually red-purple; plants with rhizomes and erect stems; leaf  blades 3–9 mm wide
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    A. stolonifera
    3b. Inflorescence with ascending to appressed branches after anthesis [Fig. 182], 3–10 (–15) cm tall, usually yellow-brown; plants without rhizomes, but with stolons  and basally decumbent stems; leaf blades 2–5 mm wide
See list of 7 species in 1b
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1b. Palea unnerved and up to 0.5 mm long or absent, less than 33% as long as the lemma; plants cespitose, without prolonged rhizomes or stolons (except A. canina, which often  has stolons)
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  A. elliottiana
  4a. Plants annual; lemmas usually with a delicate, flexuous awn (3–) 6–10 mm long; callus of the lemma densely pubescent with hairs to 0.6 mm long
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  4b. Plants perennial; lemmas with or without awns, the awns, if present, straight or geniculate and up to 5 mm long; callus of the lemma glabrous or sparsely to moderately pubescent with hairs to 0.3 mm long
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    A. exarata
    5a. Panicle dense and spike-like, with ascending to appressed lower branches  1–2 (–4) cm long that are partly concealed by the spikelets
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    5b. Panicle open, with ascending to wide-spreading lower branches 2–12 cm long that are readily visible
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      6a. Lemmas awnless (very rare individuals of A. perennans producing some spikelets with short awns to 2 mm, but these usually not exserted beyond the glumes)
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        A. perennans
        7a. Leaf blades flat, 2–5 mm wide, the basal ones usually withered by anthesis
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        7b. Leaf blades involute, 0.5–2 mm wide, the basal ones persisting all year in a tuft
        
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        A. hyemalis
        8a. Anthers globose, 0.2–0.3 (–0.5) mm long; glumes 1–2 mm long; lemmas 0.8–1.2 mm long; spikelets ± evidently clustered near the tips of the panicle branches; pedicels 0.3–2 mm long; reproductive stems often with more than  3 leaf-bearing nodes; plants flowering March through July
        
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        A. scabra
        8b. Anthers oblong, 0.4–0.8 mm long; glumes 1.8–3.4 mm long; lemmas 1.4–2 mm long; spikelets not appearing clustered; pedicels 0.5–5 mm long; reproductive stems with 3 or fewer leaf-bearing nodes; plants flowering  June through November (in part)
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      6b. Some or all lemmas with an awn (0.2–) 1.3–5 mm long, the awn produced from near or below the middle of the lemma and commonly exserted from the apex of the glumes [Fig. 181]
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        A. scabra
        9a. Leaf blades involute, 0.2–2 mm wide, the basal ones persisting all year in a tuft; reproductive stems with 3 or fewer leaf-bearing nodes (in part)
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        9b. Leaf blades flat, 1–3 mm wide, the basal ones usually withered prior to anthesis; reproductive stems with usually more than 3 leaf-bearing nodes
        
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        A. canina
        10a. Glumes 1.7–3 mm long; anthers 1–1.5 mm long; caryopses 0.8–1.2 mm long; stolons usually present
        
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        A. mertensii
        10b. Glumes 2.5–3.8 mm long; anthers 0.5–0.8 mm long; caryopses 1.4–2 mm long; stolons absent

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