Flora of the Southeastern United States
2022 Edition

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Key to Eleocharis, Key B: spikerushes with the spike about as thick as the culm (subgenus Limnochloa)

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1 Culm transversely nodose-septate (appearing jointed); culms 2-9.5 mm in diameter.
..2 Spike distinctly thicker than the culm; culms < 3 mm in diameter
..2 Spike not distinctly thicker than the culm; culms > 5 mm in diameter.
....3 Pistillate scales delicate, papery, purplish-brown with a wide greenish midrib but no other conspicuous nerves; achene faces finely, shallowly reticulate; [rare in peninsular FL]
....3 Pistillate scales (except for the hyaline margins) leathery, pale yellowish-brown, with numerous closely spaced parallel nerves; achene faces obscurely to boldly rugulose.
......4 Achene faces with longitudinal rows of enlarged linear cells separated by obscure longitudinal lines; perianth bristles slender and flexuous, finely spinulose, shorter than to equaling the achene (to 2.5 mm long); culm septae widely (>10 mm) and ± evenly spaced; [widespread in our area]
......4 Achene faces with 20-40 bold transverse-rugulose lines; perianth bristles stiff and stout, coarsely spinulose, exceeding the achene (to 2.9 mm long); culm septae concentrated proximally (below spikelet); [of Panhandle FL and s. AL]
1 Culm not transversely nodose-septate (septae incomplete, if present); culms 1-5.5 mm in diameter.
........5 Spike 3-5 mm in diameter, to 5 cm long, rounded to obtuse at the tip, densely flowered, the flowers (scales) 50-100 per spike, arranged in obvious spiral rows; culm 2-5 mm in diameter; [of estuarine and riverine marshes, or brackish interdune swale ponds on barrier islands].
..........6 Culms 3-5 mm in diameter, live culms terete when fresh; tubercle base confluent with the summit of the achene
..........6 Culms 2-4 mm in diameter, sharply 3-4-angled when fresh; tubercle base distinctly constricted, forming a "waist"
........5 Spike 1-2 mm in diameter, to 2.5 cm long, sharply pointed at the tip, loosely flowered, the flowers (scales) 10-25, few enough that the spiral arrangement is not readily apparent; culm 0.5-1.5 (-2) mm in diameter; [of limesink (doline) ponds and Carolina bay lakes of the mainland].
............7 Achene body 0.8-1.5 mm long; scales mostly ca. 3.5 mm long; culms terete when fresh
............7 Achene body 1.5-2.5 mm long; scales mostly ca. 5 mm long; culms 3-angled when fresh