1 Cauline leaves expanded at the base, usually auriculate.

  2 Siliques strongly compressed parallel to the plane of the septum (latiseptate), orbicular in outline, > 3× as wide as thick; valves pubescent with a mixture of large, simple, bulbous-based trichomes and smaller branched trichomes; flowers yellow

  2 Siliques not compressed, or slightly to somewhat compressed at right angles to the plane of the septum (angustiseptate), nearly globose, subglobose, pyriform, or slightly bilobed, < 2× as wide as thick; valves variously glabrous, pubescent with only a single type of trichome, or pubescent with a mixture of large, simple, bulbous-based trichomes and smaller branched trichomes; flowers white (to pale lavender) or yellow.

    3 Petals white or pale lavender (the claws yellowish); siliques pyriform, depressed globose, or slightly bilobed; septum (of the silique) perforate or nearly absent (rarely complete).

      4 Siliques glabrous or very sparsely pubescent, subpyriform; valves (of the silique) papery, densely pubescent on the interior; styles glabrous

      4 Siliques densely pubescent, depressed globose or slightly bilobed; valves (of the silique) glabrous on the interior; styles hirsute

    3 Petals light to rich yellow (sometimes drying purplish); siliques globose to subglobose; septum (of the silique) complete.

        5 Siliques slightly to strongly compressed at right angles to the plane of the septum (angustiseptate); fruiting pedicels recurved (bending downwards); filaments not dilated at the base; petals pale yellow (sometimes drying purplish); valves of silique densely hairy.

          6 Fruits not inflated, the valves V-shaped or even keeled in ×-section; trichomes of the stems and leaves usually simple (sometimes with an understory of smaller, branched trichomes); [s. TX]

          6 Fruits inflated, the valve outer surface rounded in ×-section; trichomes of the stems and leaves of long, coarse simple trichomes over an understory of smaller branched trichomes; [s. TX, northwards to c. TX]

        5 Siliques not compressed; fruiting pedicels straight, ascending; filaments dilated at the base; petals rich yellow; silique valves glabrous (densely hairy in P. densipila).

             7 Siliques densely hairy; styles pubescent, at least near their bases; [c. and e. TN and nc. AL]

             7 Siliques glabrous; styles glabrous; [nw. AL, OK, TX]

               8 Siliques 3-4 × 3-4 mm; ovules 4-8 per ovary; septum of silique thick, opaque; [nw. AL]

               8 Siliques 4-6 (-8) × 4-6 mm; ovules (8-) 12-28 (-40) per ovary; septum of silique thin, translucent or transparent; [OK, TX].

                 9 Lower stem hirsute with spreading, simple trichomes; lower stem leaves strongly auriculate; petals 4-5 mm wide

                 9 Lower stem pubescent with appressed, branched trichomes; lower stem leaves slightly auriculate; petals 6-9 mm wide