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Schoenoplectus

See list of 11 species in this genus

Achene measurements in the following key do not include the persistent style beak, the prominence of which varies by species and is taxonomically informative. Hybridization is frequent between some members of this genus, especially within the Schoenoplectus lacustris (L.) Palla complex (e.g., S. acutus, S. heterochaetus, S. tabernaemontani). Hybrid plants typically show reduced pollen viability and fruit set. Reference: Smith (2002b).

  • 1a. Plants submerged aquatics with flaccid leaves, often forming extensive vegetative colonies; spikelets solitary on a stiff, emergent stem
  • 1b. Plants rarely submerged, the leaf blades, when present, commonly stiffer, associated 
with reproductive shoots; spikelets usually 2 or more per inflorescence
    • 2a. Plants annual, with cespitose stems; rhizomes absent or very short (i.e., ca. 1 mm long); anthers 0.4–0.6 mm long; stems ca. 0.5–1 mm thick at the midpoint
      • 3a. Leaf-bearing nodes confined to the very base of the stem; achenes pitted to nearly smooth [Fig. 126], with or without perianth bristles; amphicarpic flowers absent
        • 4a. Achenes noticeably pitted, 1.75–2 mm long, rounded near base, biconvex; floral scales with a distinct midvein, lacking a green midstrip; perianth bristles, when present, stout and distinctly tapered apically; primary involucral bract often divergent [Fig. 125]
        • 4b. Achenes nearly smooth, 1.5–1.8 mm long, wedge-shaped near base, mostly plano-convex; floral scales with an obscure midvein, possessing a broad green midstrip; perianth bristles, when present, slender throughout [Fig. 126]; primary involucral bract usually erect
      • 3b. Leaf-bearing nodes basal and one on the stem; achenes with prominent, transverse, wavy ridges, almost always lacking perianth bristles; amphicarpic flowers frequently present, enclosed in the basal leaf sheaths
    • 2b. Plants perennial, often forming extensive colonies from elongate rhizomes; anthers 1.5–3.5 mm long; stems ca. 1–10 mm thick at the midpoint
      • 5a. Stems terete or nearly so in cross-section; basal sheaths lacking elongate blades
        • 6a. Spikelets all or mostly single at the ends of the pedicels; floral scales smooth along the margin; achenes trigonous in cross-section, with a style beak 0.3–1 mm long, with 4 (or 5) perianth bristles, usually 2 much shorter than the others
        • 6b. Spikelets all or mostly in glomerules of 2–7 at the ends of the pedicels; floral scales ciliate, at least near the apex; achenes plano-convex or with a low, abaxial ridge, with a style beak 0.1–0.5 mm long, with (5–) 6 (–7) perianth bristles, generally 
of subequal length
          • 7a. Stems firm, with 10–12 aerenchymal lacunae in cross-section at stem height, each lacuna 0.3–0.5 mm in diameter; spikelets mostly in glomerules of 3–7; floral scales with a gray background, (3–) 3.5–4 mm long, with a contorted (rarely straight) awn 0.5–2 mm long; achenes 2–2.8 mm long, with a style beak 0.2–0.5 mm long
          • 7b. Stems soft, with 2–4 aerenchymal lacunae in cross-section at stem height, each lacuna 1–2.5 mm in diameter; spikelets mostly in glomerules of 2 or 3; floral scales with a pale orange-brown to dark red-brown background, 2–3.5 mm long, with a usually straight awn 0.2–0.8 mm long; achenes 1.7–2.3 mm long, with a style beak 0.1–0.3 mm long
      • 5b. Stems sharply trigonous or even triquetrous in cross-section; basal sheaths producing elongate blades
        • 8a. Achenes equilaterally trigonous to compressed-trigonous in cross-section, with 
a prominent style beak 0.5–2 mm long; floral scales essentially entire at apex, with 
a central nerve and 2–10 faint to evident veins on the sides; leaves often half to fully as tall as the stem; apical appendage of anthers rounded, smooth
          • 9a. Inflorescence congested, lacking elongate branches, usually with 1–4 spikelets; floral scales 4–5 mm long; style beak 0.5–1 mm long
          • 9b. Inflorescence open, with elongate branches, with 3–20 pedicellate spikelets; floral scales 5–7 mm long; style beak 0.7–2 mm long
        • 8b. Achenes plano-convex to obscurely compressed-trigonous in cross-section, with a tiny style beak shorter than 0.5 mm; floral scales with an apical notch 0.1–1 mm deep from which the awn emerges, with only a single central nerve, the sides lacking veins; leaves often half as tall as stem or shorter; apical appendage of anthers elongate, spinulose along margin
          • 10a. Stems with deeply concave sides and wing-angles; primary involucral bract 1–6 cm long; floral scales with an apical notch 0.1–0.4 mm deep, with an awn 0.2–0.5 mm long; uppermost leaf blade shorter than to about equaling the length of its associated sheath
          • 10b. Stems with shallowly concave to flat sides and sharp angles; primary involucral bract 3–20 cm long; floral scales with an apical notch (0.3–) 0.5–1 mm deep, with an awn 0.5–1.5 (–2.5) mm long; uppermost leaf blade usually several times longer than its associated sheath

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