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 adjacent 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 (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 exotic]; [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