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| 1 Leaves cauline, opposite; spikes on peduncles from the leaf axils; [subgenus Psyllium, section Psyllium] |
| 1 Leaves basal; spikes on scapes from the base of the plant. |
| ..2 Leaves pinnatifid; [subgenus Coronopus, section Coronopus] |
| ..2 Leaves unlobed and either entire or toothed (if so, obscurely so in most species). |
....3 Leaf venation pinnate, some major veins departing from the midvein well above the leaf base; summer and winter leaves dimorphic, the winter leaves lanceolate (typically submersed), the summer leaves ovate or cordate (emersed except in floods); plants perennial from a thick, fleshy rootstock that is typically 3-8 cm wide near its summit, with a cavity below (like an inverted bowl), and with 3-10 fleshy roots 3-15 mm thick descending or spreading from the bowl rim; capsule 2-4-seeded; scapes hollow and terete; [aquatic or semi-aquatic]; [subgenus Plantago, section Heptaneuron] |
| ....3 Leaf venation parallel, with all of the major veins separating at the base of the leaf blade; leaves not dimorphic; plants either perennial from thin, fibrous roots or an erect caudex, or annual from a small taproot; capsule 2-30-seeded; scapes solid, terete or 5-angled; [terrestrial or wetland]. |
| ......4 Leaves ovate to broadly lanceolate or broadly oblanceolate, 1-10× as long as wide, distinctly broadened upward from a petiolar base, the larger leaves > 1 cm wide. |
| ........5 Leaves broadly ovate-elliptic, the blades 1-3× as long as wide, distinctly petiolate; scapes solid and terete. |
| ..........6 Bracts and sepals flat or slightly keeled; seeds 2-4 per capsule; primary roots thickened, tuberous near junction with the stem and leaves; spikes grayish or whitish, shiny, densely flowered such that the corolla lobes of adcent flowers often overlap; [subgenus Plantago, section Lamprosantha] |
| ..........6 Bracts and sepals conspicuously keeled; seeds 4-22 (-34) per capsule; primary roots all slender and filamentous; spikes brownish or greenish, dull, sparsely to moderately densely flowered, such that the corolla lobes of adjacent flowers do not overlap. |
| ............ 7 Fruit (3-) 4-6 mm long, dehiscent below the middle (the terminal portion about 2× as long as the basal); sepals narrowly elliptic, 2-4× as long as wide, mostly acute; petioles usually purple and glabrous at the base; well-developed leaves with 5-7 major veins; seeds 4-10 per capsule, each 1.5-2.0 (-2.5) mm long; [subgenus Plantago, section Pacifica] |
| ............ 7 Fruit (2-) 2.5-4 mm long, dehiscent near the middle (the terminal portion about as long as the basal); sepals broadly ovate, ca. 1.5× as long as wide, mostly obtuse; petioles usually green and pubescent at the base; well-developed leaves with 3-5 major veins; seeds (4-) 6-22 (-34) per capsule, each 0.7-1.7 mm long; [subgenus Plantago, section Plantago]. |
| ............ ..8 Fruit rounded to pointed at apex; seeds (4-) 6-11 (-13) per fruit; leaf blades membranaceous to fleshy-herbaceous, glabrous or pubescent; petioles elongate and slender; [widespread in our region] |
| ............ ..8 Fruit broadly rounded at apex; seeds 14-22 (-34) per fruit; leaf blades subcoriaceous-fleshy, usually pubescent; petioles short and broad; [estuarine shores, DE northwards] |
| ........5 Leaves mostly broadly oblanceolate, broadly lanceolate, or spatulate, (3-) 4-10× as long as wide, attenuate to the only somewhat petiolar base; scapes solid and 5-angled, or hollow (to solid) and terete. |
| ............ ....9 Bracts and calyx glabrous; perennial, flowering Apr-Nov. |
| ............ ......10 Spikes very densely flowered, the rachis hidden; scape 5-angled; [widespread weedy alien]; [subgenus Plantago, section Lancifolia] |
| ............ ......10 Spikes loosely flowered, the rachis visible its entire length; scape terete; [rare native of Coastal Plain pinelands and adjacent fire-plow lines and ditches]; [subgenus Plantago, section Pacifica] |
| ............ ....9 Bracts and calyx pubescent, at least on the keels; annual or perennial; flowering late Mar-Aug; [subgenus Plantago, section Virginica]. |
| ............ ........11 Perennial from a caudex; flowering Jun-Aug; upper leaf surface floccose; [local adventive, Panhandle FL] |
| ............ ........11 Ephemeral annual from a taproot, flowering late Mar-Jun, and then senescing; upper leaf surface glabrate or pilose; collectively widespread and common]. |
| ............ ..........12 Mature seeds 2.5-3 mm long, dark red, nearly flat on both sides; sepals 2.7-3.6 mm long, with an excurrent midrib; leaves typically toothed; [rare adventive in western part of our area] |
| ............ ..........12 Mature seeds 1.5-2 mm long, yellowish, tan, or brown, concave on one side, convex on the other; sepals 1.5-2.4 mm long, obtuse to rounded; leaves entire; [common in our area] |
| ......4 Leaves linear or narrowly lanceolate, (8-) 10-25× as long as wide, only slightly (if at all) broadened upward, the base not petiolar, the leaves typically < 1 cm wide. |
| ............ ............ 13 Leaves fleshy; corolla tube pubescent on its outer surface; plants perennial; [of sea beaches, in our region from e. VA northwards]; [subgenus Coronopus, section Maritima] |
| ............ ............ 13 Leaves herbaceous; corolla tube glabrous on its outer surface; plants annual; [of various habitats, collectively widespread]. |
| ............ ............ ..14 Seeds (3-) 4-25 (-30) per capsule; corollas radially symmetrical, the lobes 0.5-1 mm long; stamens 2; [subgenus Plantago, section Micropsyllium] |
| ............ ............ ....15 Seeds 0.5-0.8 mm long; capsules with 10-25 (-30) seeds |
| ............ ............ ....15 Seeds 0.8-2.5 mm long; capsules with (3-) 4-9 (-12) seeds. |
| ............ ............ ......16 Corolla lobes spreading to even reflexed; capsules with (3-) 4-9 (-12) seeds; seeds 1.5-2.5 mm long |
| ............ ............ ......16 Corolla lobes erect, connivent into a beak; capsules with 4 seeds; seeds 0.8-1.3 mm long |
| ............ ............ ..14 Seeds 2 per capsule; corollas bilaterally or radially symmetrical, the lobes 1.3-3.6 mm long; stamens 4; [subgenus Psyllium, section Gnaphaloides]. |
| ............ ............ ........17 Corollas radially symmetrical; bases of the corolla lobes obtuse or slightly cordate; [c. and nc. TX and westwards] |
| ............ ............ ........17 Corollas bilaterally symmetrical; seeds 3.2-3.8 mm long; [collectively widespread]. |
| ............ ............ ..........18 Stems (below the lowermost flowers) 20-40 cm long; bracts subtending the flowers either 2-3 mm long or 10-30 mm long. |
| ............ ............ ............ 19 Bracts subtending the flowers 10-30 mm long; uppermost corolla lobe 1.4-2.3 mm long |
| ............ ............ ............ 19 Bracts subtending the flowers 2-3 mm long; uppermost corolla lobe 2.4-3.0 mm long |
| ............ ............ ..........18 Stems 0-15 mm long; bracts 1.5-10 mm long; [mainly OK and TX westwards, rarely adventives eastwards]. |
| ............ ............ ............ ..20 Leaves 4-10 mm wide, the margins toothed, the teeth to 4 mm long (rarely entire); corolla lobes 2.2-2.5 mm long |
| ............ ............ ............ ..20 Leaves 1-4 mm wide, the margins entire (rarely toothed); corolla lobes 1.6-2.1 mm long |
| 1 Leaves peltate. |
| ..2 Leaf blades oval in shape, ca. 1.5-2× as long as wide, at maturity floating on the water’s surface; underwater portions of fresh plant coated in transparent mucilage |
| ..2 Leaf blades orbicular in shape, ca. 1× as long as wide, at maturity floating on the water’s surface, emersed, or submersed; underwater portions of fresh plant not mucilaginous (though possibly with green algae, etc.). |
| ....3 Leaves small, < 8 cm in diameter, at maturity emersed or submersed |
| ....3 Leaves large, > 20 cm in diameter, at maturity floating on the water’s surface or emersed |
| 1 Leaves not peltate, the petiole attached at a cuneate, cordate, or sagittate base. |
| ......4 Leaf blades cuneate, rounded, or truncate at the base. |
| ........5 Basal leaves lanceolate, 3-6 mm long |
| ........5 Basal leaves variously shaped, > 10 mm long. |
..........6 Main veins palmate from the leaf base and also diverging from the midvein, the secondary and tertiary veins then reticulating; inflorescence a spike; [Eudicots] |
| ..........6 Main veins either parallel or palmate from the leaf base with cross-veins at nearly right angles to the main veins; inflorescence either a diffuse raceme or panicle of white flowers, or a linear spadix of tightly packed golden-yellow flowers; [Monocots]. |
| ............ 7 Inflorescence diffuse, a raceme or panicle with whorled branches or pedicels, the flowers widely spaced and white; leaves green, “wettable” |
| ............ 7 Inflorescence tightly packed with flowers, an elongate, golden yellow spadix; leaves blue-green, “unwettable” |
| ......4 Leaf blades cordate or sagittate at the base. |
| ............ ..8 Leaf blades sagittate, the two lobes distinctly acute; leaf apex acute; leaf blade 1.3-3× as long as wide |
| ............ ..8 Leaf blades cordate, the two lobes rounded or sub-acute; leaf apex rounded or apiculate; leaf blade 0.8-8× as long as wide. |
| ............ ....9 Leaf blade margins serrate, dentate, and/or incised |
| ............ ....9 Leaf blade margins entire or obscurely crenate. |
| ............ ......10 Flowers 4-5-merous (sepals 4-5, petals 4-5, stamens 4-5); [Eudicots] |
| ............ ........11 Leaves emersed or submersed, on stout, stiff petioles (the submersed and winter leaves cuneate-based and lanceolate); flowers 4-merous (sepals 4, petals 4, stamens 4); inflorescence a spike |
| ............ ........11 Leaves floating, on slender, flexuous petioles (all leaves cordate-based); flowers 5-merous (sepals 5, petals 5, stamens 5); inflorescence an umbel |
| ............ ......10 Flowers 3-merous or many (>5-) -merous; [Basal Angiosperms or Monocots]. |
| ............ ..........12 Perianth parts numerous (usually showing differentiation into sepals and petals, though often with some intergradation), borne in a spiral; stamens numerous; leaves usually > 10 cm long or > 10 cm wide, or both (a few northern species of Nymphaea with leaves as small as 2.5 cm × 2.5 cm); [Basal Angiosperms] |
| ............ ..........12 Perianth parts 3-6 (either differentiated or not into sepals and petals); stamens either 3, or 9-12 (-18), or >20; leaves 1-10 cm long, 1-10 cm wide; [Monocots]. |
| ............ ............ 13 Perianth strongly differentiated, the 3 sepals green, leathery, and persistent, the 3 petals yellow or white, delicate, deciduous; stamens 20 or more |
| ............ ............ 13 Perianth not strongle differentiated, the sepals petaloid and similar in texture and color to the petals; stamens 10 or fewer. |
| ............ ............ ..14 Flowers unisexual, white, the sepals and petals separate; stamens 3, 6, 9, 12, 15, or 18; leaves either with a central area of spongiform cells (most easily seen on the lower leaf surface) (Limnobium), or without spongiform cells (Ottelia) |
| ............ ............ ..14 Flowers bisexual, white to blue, the perianth segments united below into a perianth tube 3-45 mm long; stamens 3; leaves lacking a central area of spongiform cells |