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1 Leaf margins conspicuously serrate; stem flattened; fruit beak 2-3 mm long; turions commonly formed, hard |
1 Leaf margins entire (sometimes crispate, but without serrations); stem terete; fruit beak < 1 mm long; turions rarely formed. |
2 Submersed leaves clasping the stem; floating leaves absent. |
3 Leaf apex boat-shaped (curved upward adaxially), splitting when pressed; stipules usually persistent, conspicuous; rhizomes with rusty-red spots; [n. PA northward] |
3 Leaf apex not boat-shaped (instead, flattened and not curved upward); stipules deciduous or becoming fibrous; rhizomes without spots; [collectively widespread]. |
4 Leaves orbicular to ovate, often lanceolate in soft water, 1-6 cm long, with 3-25 delicate veins; stipules deteriorating and deciduous (otherwise delicate and lacking fibers), absent on lower portions of stem |
4 Leaves ovate- lanceolate to narrowly lanceolate, 1.6-13 cm long, with 3-35 coarse veins; stipules disintegrating to persistent fibers, even on lower portions of stem |
2 Submersed leaves not clasping the stem (sometimes slightly clasping in P. alpinus), with or without petioles; floating leaves absent or present. |
5 Submersed leaves with petioles 1-13 cm long. |
6 Larger submersed leaves acute at the apex with a sharp awl-like tip; fruit gray-green to olive-green, with well-developed lateral ridges |
6 Larger submersed leaves acute at the apex but lacking a sharp awl-like tip; fruit red to reddish-brown, with muricate lateral ridges |
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7 Submersed leaves 27-37 veined, distinctly arcuate; lacunae absent |
7 Submersed leaves with 3-19 veins, not arced; lacunae in 1-6 rows on each side of midvein ( lacunae occasionally absent in P. alpinus). |
8 Stems conspicuously black-spotted; submersed leaves crisped along the margin; floating leaves 15-21 veined |
8 Stems lacking spots or inconspicuously spotted; submersed leaves entire or crispate; floating leaves 3-29 veined |
9 Submersed leaf blades typically reddish-green colored (especially upon drying), with 7 veins (sometimes with 6 additional obscure veins) and a conspicuous reticulate pattern along midvein; fruit stalked, turgid; [NJ and PA, northward] |
9 Submersed leaf blades green or brownish-green, with 7-19 ( P. illinoensis) or 3-9 conspicuous veins ( P. gramineus), without a reticulate portion along midvein; fruit sessile, laterally compressed; if submersed leaves with < 7 veins, then leaves typically 1.5-4.5 cm long and and stipules acute; [collectively widespread]. |
10 Stems commonly branched; submersed leaves with (3-) 5-9 veins, rarely crispate; lacunae in 1-2 rows on each side of midrib; fruit 1.7-2.8 mm long, with obsolete or rounded keel, reddish-brown colored; [n. VA west to s. IL, northward] |
10 Stems rarely branched; submersed leaves with 7-19 veins, often crispate; lacunae in 2-5 rows on each side of midrib; fruit 2.5-3.5 mm long, with well-developed keel, gray-green or olive-green colored; [throughout our flora region] |