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Key to Brassicaceae, Key A: plants in flower, trichomes of plant absent or, if present, unbranched

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1 Flowers (all, or at least many) solitary on scapes
1 Flowers in racemes.
  2 Flowers yellow.
    3 Leaves auriculate, sagittate, or amplexicaul at base.
      4 Upper stems glaucous.
        5 Petals 6-30 mm long, clawed
        5 Petals 2-4 mm long, not clawed
      4 Upper stems green.
          6 Stems angular distally; blooming Apr to early Jun
          6 Stems not angular distally; blooming Apr to Oct
    3 Leaves not clasping at base.
             7 Petals with contrasting dark yellow, brown, maroon, or purple veins; [tribe Brassiceae]
               8 Petals yellow; basal leaves with 3-10 lobes per margin; stems usually sparsely to densely hispid basally; cauline leaf blades usually lobed (but fewer than basal leaves)
               8 Petals yellow or creamy white; basal leaves with 1-4 lobes per margin; stems sparsely to densely pubescent; cauline leaf blades often undivided
             7 Petals mostly uniform in color.
                 9 Ovaries and young fruits 2-segmented; petals 5-30 mm long; [tribe Brassiceae]
                   10 Stem leaves pinnatifid
                   10 Stem leaves entire, serrate, or sinuate
                     11 Valves of the fruit 1-veined; sepals erect or ascending (rarely spreading); terminal segment of fruit conic, usually seedless
                     11 Valves of the fruit 3-7-veined (1-veined in Rhamphospermum nigrum); sepals spreading to reflexed; terminal segment of fruit either linear or ensiform (flattened and 2-edged).
                       12 Terminal segment of fruit linear 0.1-1.6 cm long, seedless or 1-seeded.
                       12 Terminal segment of fruit ensiform (flattened and 2-edged), (1-) 1.5-2.5 (-3) cm long, seedless
                 9 Ovaries and young fruits unsegmented; petals 1-8 mm long.
                          13 Inflorescence leafy bracteate (most of the pedicels subtended by bracts)
                          13 Inflorescence not bracteate (occasionally with some lower pedicels bearing bracts).
                            14 Stigmas distinctly 2-lobed; [tribe Sisymbrieae]
                            14 Stigmas entire, rarely indistinctly 2-lobed; [tribe Cardamineae]
  2 Flowers white, cream, pinkish, purple, lavender, or blue.
                              15 Leaves strictly basal, or both basal and cauline and also auriculate.
                                16 Plants with only basal leaves or cauline leaves much reduced.
                                  17 Plants annual; flowers zygomorphic; petals 0.5-2.5 mm long; [tribe Iberideae]
                                  17 Plants annual or perennial; flowers actinomorphic; petals absent, rudimentary, or to 16 mm long; [tribe Cardamineae]
                                16 Plants with some well-developed cauline leaves.
                                    18 Ovaries and young fruits ovate, orbicular or cordate.
                                       19 Ovules 1 per ovary; [tribe Calepineae]
                                       19 Ovules >1 per ovary.
                                         20 Ovules 2 (rarely 4) per ovary; [tribe Lepidieae]
                                         20 Ovules 6-16 per ovary.
                                           21 Leaves mostly entire; plants not fetid; [tribe Noccaeeae]
                                           21 Leaves often toothed; plants fetid; [tribe Thlaspideae]
                                    18 Ovaries and young fruits linear.
                                             22 Plants aquatic or semi-aquatic; rooting at nodes; [tribe Cardamineae]
                                             22 Plants terrestrial, though sometimes growing partially submerged; not rooting at nodes.
                                               23 Flowers blue, rarely pink or white; petals 12-32 mm long; [tribe Brassiceae]
                                               23 Flowers white, sometimes pink or purple; petals <16 mm long.
                                                 24 Petals larger, conspicuous, 7-16 mm long.
                                                    25 Cauline leaves simple or pinnately to palmately compound, typically not auriculate; if simple and auriculate, then plants usually with a mix of compound and simple cauline leaves and the simple leaves ovate or oblong and never deeply pinnatifid (as in C. clematitis)
                                                    25 Cauline leaves conspicuously or slightly auriculate, always simple; blades elliptic, lanceolate, ovate, or oblong, deeply pinnatifid to entire
                                                      26 Basal leaves oblanceolate, unlobed; petals white to cream
                                                      26 Basal leaves incised or lyrate-lobed; petals white to pinkish-purple
                                                 24 Petals smaller, inconspicuous, < 7 mm long.
                                                        27 Cauline leaves sessile; [tribe Boechereae]
                                                        27 Cauline leaves usually petiolate; [tribe Cardamineae]
                              15 Leaves basal and cauline but not auriculate (basal leaves sometimes withering upon flowering, thus only appearing alternate).
                                                          28 Plants aquatic, rooting at nodes; [tribe Cardamineae].
                                                            29 Submersed leaves dissected into filiform segments
                                                            29 Leaves not dissected into filiform segments
                                                          28 Plants terrestrial, though sometimes growing partially submersed; not rooting at nodes.
                                                              30 Stamens 2 or 4 (per individual flower).
                                                                 31 Ovaries and young fruits linear; [tribe Cardamineae]
                                                                 31 Ovaries and young fruits ovate, orbicular or cordate.
                                                                   32 Flowers zygomorphic; filaments appendaged; [tribe Iberideae]
                                                                   32 Flowers actinomorphic; filaments not appendaged; [tribe Lepidieae]
                                                              30 Stamens 6 (per individual flower).
                                                                     33 Petals 15-30 mm long; fruit conspicuously coin-like, oblong to suborbicular and latiseptate (flattened parallel to septum); [tribe Lunarieae]
                                                                     33 Petals rarely to 20 mm long; fruit ovate to linear (if rounded not strongly flattened like a coin, or if flattened the fruit long and slender as in Warea).
                                                                       34 Inflorescence corymbose; claws (of the petals) strongly differentiated from blades; fruit latiseptate and stipitate, linear in shape; [natives of sandhills and coastal plain, NC to s. MS]
                                                                       34 Inflorescence elongate or corymbose (if so, not also collectively as above); claws differentiated or not from blades; fruit terete, latiseptate, or augustiseptate (flattened perpindicular to septum), stipate or not, linear to ovate in shape; [widespread natives and non-natives]
                                                                         35 Ovaries and young fruits 2-segmented; [tribe Brassiceae]
                                                                         35 Ovaries and young fruits unsegmented.
                                                                           36 Ovaries and young fruits ovate, orbicular or cordate; [tribe Lepidieae]
                                                                              37 Ovules 8-12 per ovary
                                                                              37 Ovules 2 (-4) per ovary
                                                                           36 Ovaries and young fruits linear.
                                                                                38 Petals with contrasting dark veins; [tribe Brassiceae]
                                                                                38 Petals mostly uniform in color.
                                                                                  39 Leaves smelling of garlic when crushed, reniform or cordate, dentate; [tribe Thlaspideae]
                                                                                  39 Leaves not smelling of garlic, rarely reniform or cordate, with margins various.
                                                                                    40 Cauline leaves sessile; [tribe Boechereae]
                                                                                    40 Cauline leaves usually petiolate; [tribe Cardamineae].
                                                                                      41 Base of plant usually glabrous; seeds not winged
                                                                                      41 Base of plant pubescent; seeds winged