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| 1 Leaf blades sagittate or cordate (at least some of the leaves on a plant with sagittate or cordate basal lobes); some species are keyed both here and below). |
| ..2 Sepals appressed in fruit; lower flowers bisexual, the stamens either functional or not; stamen filaments roughened with minute scales (except glabrous in S. spatulata); [subgenus Lophotocarpus]. |
| ....3 Leaves primarily phyllodial, lanceolate or spatulate (sagittate leaves rare in the population and few on a given plant); flowers in 1-2 (-3) whorls; stamen filaments glabrous (use 10×); [native, tidal marshes] |
| ....3 Leaves primarily sagittate (phyllodial leaves rare in the population and few on a given plant); flowers in 3-12 whorls; stamen filaments roughened with minute scales (use 10×); [either introduced aliens, sometimes in tidal marshes, or native, in inland alkaline sites]. |
| ......4 Plants with floating, sagittate blades; inflorescences floating; achene faces tuberculate |
| ......4 Plants with emersed, sagittate blades; inflorescences emersed; achene faces smooth. |
| ........5 Petals white, immaculate; stamens of pistillate flowers functional; [inland sites, native or introduced at a given locality] |
| ........5 Petals white, with a purple spot at the base; stamens of pistillate flowers generally nonfunctional; [exotic, introduced around coastal ports] |
| ..2 Sepals reflexed or at least widely spreading in fruit; lower flowers pistillate; stamens glabrous (except roughened with minute scales in S. rigida); [subgenus Sagittaria]. |
| ..........6 Leaves cordate basally, floating; stalks of the pistillate flowers stout, reflexed in fruit; stamens mostly fewer than 15 |
| ..........6 Leaves sagittate basally, emersed; stalks of the pistillate not notably stout, ascending in fruit; stamens 15 or more. |
| ............ 7 Beak of the achene lateral (at a right angle to the long axis of the achene); bracts of the inflorescence 2-15 mm long, boat-shaped, obtuse or broadly acute. |
| ............ ..8 Lowermost (pistillate) flowers sessile or on short pedicels (to 5 mm or rarely 10 mm long), the pedicels of the lowermost flowers notably shorter than those in whorls above; inflorescence normally bent at the lowest whorl of flowers; stamen filaments minutely roughened with minute scales |
| ............ ..8 Lowermost (pistillate) flowers on long pedicels (at least 20 mm), the pedicels of the lowermost flowers longer than those in whorls above; inflorescence normally not bent; stamen filaments glabrous. |
| ............ ....9 Basal lobes of the leaf > 2× as long as the blade body (the terminal lobe); basal lobes of the leaf narrow, < 2.5 cm wide even at their bases; achene beak 1-2 mm long, lateral and horizontal; achene faces tuberculate; [OK and TX westwards] |
| ............ ....9 Basal lobes of the leaf < 1.5× as long as the blade body (the terminal lobe); basal lobes of the leaf broad or less commonly narrow, usually > 2.5 cm wide at their bases; achene beak 0.1-0.6 mm long, lateral and ascending; achene faces smooth; [widespread in our region]. |
| ............ ......10 Leaf blades glabrous; achene faces with resin ducts |
| ............ ......10 Leaf blades rather densely fine-pubescent; achene faces lacking resin ducts |
| ............ 7 Beak of the achene terminal (extending along the long axis of the achene); bracts of the inflorescence 5-40 mm long, either blunt or acuminate, not boat-shaped. |
| ............ ........11 Bracts of the inflorescence thick and herbaceous, 5-25 mm long, rounded at the tip; flowers in 2-4 whorls; achenes with facial resin-ducts; [acidic, blackwater habitats of the Coastal Plain] |
| ............ ........11 Bracts of the inflorescence papery and tan, 7-40 mm long, acuminate at the tip; flowers in 5-12 whorls; achenes without resin-ducts; [primarily other habitats, collectively widespread]. |
| ............ ..........12 Bracts connate at least ¼ total length, leaves emersed but also often floating or submerged. |
| ............ ..........12 Bracts distinct or connate much less than ¼ total length; leaves emersed only. |
............ ............ 13 Petiole sharply 5-wing-angled in cross-section; inflorescence unbranched; fruiting heads 1.0-1.5 cm in diameter, globular |
| ............ ............ 13 Petiole corrugated but not wing-angled in cross-section; inflorescence often branched at the base; fruiting heads (1.2-) 1.7-2.2 cm in diameter, often globular-depressed |
| 1 Leaf blades linear, lanceolate, or ovate, or modified as linear, bladeless phyllodia, these often of spongy texture. |
| ............ ............ ..14 Stalks of the pistillate flowers reflexed in fruit, often stout; stamen filaments glabrous (except roughened with minute scales in S. platyphylla and S. calycina). |
| ............ ............ ....15 Sepals appressed in fruit; lower flowers bisexual, the stamens either functional or not; [subgenus Lophotocarpus]. |
| ............ ............ ......16 Leaves generally primarily sagittate (phyllodial leaves generally rare in the population); flowers in 3-12 whorls; stamen filaments roughened with minute scales (use 10× magnification); [inland alkaline sites] |
| ............ ............ ......16 Leaves primarily phyllodial, lanceolate or spatulate (sagittate leaves rare in the population and few on a given plant); flowers in 1-2 (-3) whorls; stamen filaments glabrous (use 10× magnification); [tidal marshes] |
| ............ ............ ....15 Sepals reflexed or at least widely spreading in fruit; lower flowers pistillate; [subgenus Sagittaria]. |
| ............ ............ ........17 Plant generally with erect, emersed leaves with well-developed blades with firm texture, the blades 2-8 cm wide. |
| ............ ............ ..........18 Fruiting pedicels ascending, filaments not dilated |
| ............ ............ ..........18 Fruiting pedicels spreading to recurved, filaments dilated |
| ............ ............ ........17 Plant with all leaves phyllodial, if expanded at the summit, the expanded blade of weak texture, floating. |
| ............ ............ ............ 19 Leaves 2-10 (-30) cm long, 3-8 mm wide (sometimes with dilated tip to 20 mm wide); [tidal, fresh to brackish waters] |
| ............ ............ ............ 19 Leaves 30-300 (or more) cm long, either 1-3 or 7-14 mm wide; [nontidal waters]. |
| ............ ............ ............ ..20 Leaves very variable from population to population, in swiftly flowing black water typically about 100 cm long and 1-3 mm wide, in more stagnant water (or when emersed by dropping water levels, typically with lax petioles and floating blades, the blades lanceolate, or elliptic, the base cuneate, rounded, or cordate; [blackwater streams and ponds, MA south to FL, west to s. AL] |
| ............ ............ ............ ..20 Leaves 100-300 (or more) cm long, 7-14 mm wide; [springs and spring-runs, endemic to FL] |
| ............ ............ ..14 Stalks of the pistillate flowers ascending or spreading in fruit, not notably stout; stamen filaments roughened with minute scales (except glabrous in S. engelmanniana, S. papillosa, and S. ambigua). |
| ............ ............ ............ ....21 Stamen filaments linear, less thick than the anther, changing little in diameter from near base to near summit. |
| ............ ............ ............ ......22 Leaves all phyllodial, without flattened blades; bracts of the inflorescence strongly papillose; [s. MS westward] |
| ............ ............ ............ ......22 Leaves with flattened blades; bracts of the inflorescence smooth, papillose, or longitudinally striate; [collectively widespread] |
| ............ ............ ............ ........23 Bracts of the inflorescence firm or delicate in texture, smooth; stamen filaments glabrous; [of inland wetlands] |
| ............ ............ ............ ..........24 Achenes 1.5-2.1 mm long, 0.8-1.5 mm wide; [inland circumneutral wetlands, west of the Mississippi River] |
| ............ ............ ............ ..........24 Achenes 2.4-4 mm long, 1.5-3.8 mm wide; [inland acidic wetlands, east of the Mississippi River] |
| ............ ............ ............ ........23 Bracts of the inflorescence either papillose or longitudinally striate-ribbed; stamen filaments roughened with minute scales; [estuarine areas and associated nontidal wetlands]. |
| ............ ............ ............ ............ 25 Bracts and sepals striate-ribbed; stamen filaments 2-5 mm long; [rare, from e. SC southward] |
| ............ ............ ............ ............ 25 Bracts and sepals papillose; stamen filaments 1.5-3.5 mm long; [common, throughout our coastal area] |
| ............ ............ ............ ....21 Stamen filaments either distinctly dilated toward the base (often broadly conic) or thickened throughout, the filament (at least basally) as thick or thicker than the anther. |
| ............ ............ ............ ............ ..26 Lowermost (pistillate) flowers sessile or on short pedicels (to 5 mm or rarely 10 mm long); inflorescence normally bent at the lowest whorl of flowers |
| ............ ............ ............ ............ ..26 Lowermost (pistillate) flowers on longer pedicels; inflorescence normally not bent. |
| ............ ............ ............ ............ ....27 Leaves all phyllodia, the phyllodia terete or nearly so. |
| ............ ............ ............ ............ ......28 Phyllodia of emersed flowering plants elongate (1/2-1× as long as scape), slender, emersed or laxly ascending and submersed in water; phyllodia of stranded flowering plants elongate (1/3-1× as long as scape, but may be shorter), relatively stiff; [se. NC and southward] |
| ............ ............ ............ ............ ......28 Phyllodia of emersed flowering plants short (2-8 cm), very thick, deeply submersed; when plants are stranded, phyllodia of stranded flowering plants elongate (1/2-1× as long as scape), slender, stiffly erect; [DE-MD and northward] |
| ............ ............ ............ ............ ....27 Leaves with blades and petioles, or if all phyllodia, the phyllodia flattened on upper surface or triangular in cross-section; [collectively widespread]. |
| ............ ............ ............ ............ ........29 Plants with corms and/or stolons, lacking coarse rhizomes. |
| ............ ............ ............ ............ ..........30 Blades of emersed leaves lanceolate, narrowly spatulate, > 5 mm wide; [Mountain and upper Piedmont bogs, swamp forests, and adjacent ditches] |
| ............ ............ ............ ............ ..........30 Blades of emersed leaves linear (< 3 mm wide, rarely to 4 mm) or phyllodial; [Coastal Plain depression ponds and impoundments] |
| ............ ............ ............ ............ ............ 31 Achenes 1.5-2.0 (-2.5) mm long; achene faces with 3 or more keels and 2 or more resin ducts; inflorescence bracts connate for > 50% of length; [se. NC and southward] |
| ............ ............ ............ ............ ............ 31 Achenes (2.2-) 2.4-3.0 mm long; achene faces with 2-3 keels and 1-2 resin ducts; inflorescence bracts connate for < 40% of length; [restricted to Sandhills region of NC and SC, likely in e GA] |
| ............ ............ ............ ............ ........29 Plants with coarse rhizomes, lacking corms and stolons. |
| ............ ............ ............ ............ ............ ..32 Abaxial wing of fruit scalloped or toothed; [n. AL and nw. GA] |
| ............ ............ ............ ............ ............ ..32 Abaxial wing of fruit entire; [collectively widespread]. |
| ............ ............ ............ ............ ............ ....33 Larger phyllodes 0.8-2.5 cm wide, the apices blunt (rarely acute); longer pistillate pedicels 2-5 (-6.5) cm long; median resin duct of mature achene linear, about as wide as the posterior duct (or ducts absent) |
| ............ ............ ............ ............ ............ ....33 Larger phyllodes to 1 cm wide (except sometimes wider in S. chapmanii), the apices acute; longer pistillate pedicels 1-4 cm long; median resin duct of mature achene club-shaped and 2× the diameter of the posterior duct. |
| ............ ............ ............ ............ ............ ......34 Inflorescence branched at the base (in at least some plants of a population); bracts of the inflorescence only slightly connate, the free tips narrowly triangular, 6-15 mm long |
| ............ ............ ............ ............ ............ ......34 Inflorescence unbranched at the base; bracts of the inflorescence slightly to almost fully connate |