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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

Key to Brassicaceae, Key C: plants in fruit, trichomes of plant absent or, if present, unbranched

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1 Fruits silicles (< 3× as long as wide).
  2 Fruits 2-segmented
    3 Plants succulent, leaves usually fleshy
    3 Plants herbaceous, not succulent, leaves not fleshy
  2 Fruits unsegmented.
      4 Fruits 2 cm or more wide
      4 Fruits < 2 cm wide.
        5 Fruits with 20 or more seeds
        5 Fruits with 16 or fewer seeds.
          6 Fruits with 1 seed.
             7 Plants > 5 dm tall
             7 Plants < 5 dm tall
          6 Fruits with 2-16 seeds.
               8 Fruits with 2 seeds
               8 Fruits with more than 2 seeds.
                 9 Leaves pinnately lobed
                   10 Stems 5-12 (-20) dm tall; leaf blades of basal leaves (3-) 5-12 (-17) cm long
                   10 Stems 0.5-1.5 (-2) dm tall; leaf blades of basal leaves 0.3-1.5 (-2) cm long
                 9 Leaves not lobed.
                     11 Plants not fetid; seeds usually smooth, yellowish to medium brown
                     11 Plants fetid; seeds striate or alveolate, dark gray to dark brown or black
1 Fruits siliques (> 3× as long as wide).
                       12 Fruits indehiscent or breaking into 1-seeded segments.
                          13 Fruits not segmented, 1-seeded
                          13 Fruits segmented, usually more than 1-seeded.
                            14 Styles obsolete; plants glabrous; [coastal]
                            14 Styles 1-5 mm; plants pubescent; [inland]
                       12 Fruits dehiscent, more than 1-seeded.
                              15 Fruits segmented.
                                16 Cauline leaf blade bases auriculate (except B. juncea); terminal silique segment seedless (rarely 1-2-seeded), conic
                                16 Cauline leaf blade bases not auriculate; terminal silique segment 1-5-seeded (sometimes 0).
                                  17 Fruit valves 1-veined
                                  17 Fruit valves 3-7-veined.
                                    18 Valves of the fruit 3-5 (-7) veined.
                                       19 Terminal segment of fruit linear 0.1-1.6 cm long, seedless or 1-seeded.
                                       19 Terminal segment of fruit ensiform (flattened and 2-edged), (1-) 1.5-2.5 (-3) cm long, seedless
                              15 Fruits unsegmented.
                                         20 Fruits (all, or at least some) solitary, borne on scapes
                                         20 Fruits in racemes (or corymbose clusters).
                                           21 Fruits latiseptate (flattened parallel to the septum).
                                             22 Replums strongly flattened; fruit valves dehiscing elastically, coiled
                                             22 Replums terete or rounded; fruit valves not dehiscing elastically or coiled.
                                               23 Seeds not winged.
                                                 24 Fruit stipitate; cauline leaves entire, not auriculate; flowers pink to purple (or white in W. carteri), [natives of sandhills and coastal plain, NC to s. MS]
                                                 24 Fruit sessile or short-stipitate; cauline leaves usually lobed or at least dentate, the bases auriculate or somewhat clasping; flowers yellow; [non-natives, widespread]
                                               23 Seeds winged at least distally.
                                                    25 Cauline leaves pinnatifid or pinnatisect
                                                    25 Cauline leaves entire or dentate
                                           21 Fruits terete or 4-angled.
                                                      26 Plants aquatic or semi-aquatic; rooting at nodes
                                                      26 Plants terrestrial, though rarely growing partially submersed; not rooting at nodes.
                                                        27 Fresh leaves smelling of garlic when crushed, reniform or cordate, dentate
                                                        27 Fresh leaves not smelling of garlic when crush, rarely reniform or cordate, dentate or not.
                                                          28 Seeds biseriate
                                                          28 Seeds uniseriate.
                                                            29 Stigma lobes obviously decurrent
                                                            29 Stigma lobes sometimes distinct but not decurrent.
                                                              30 Lower cauline leaves entire or dentate.
                                                                 31 Cauline leaves spaced, not concealing stem, spreading to slightly ascending; petals 7-12 mm long
                                                                   32 Basal leaves obovate to oblanceolate, unlobed; cauline leaves entire; siliques 8-13 cm long
                                                                   32 Basal leaves incised or lyrate-lobed; cauline leaves with dentate to serrate margins; siliques 2-4 cm long
                                                                 31 Cauline leaves usually ascendant and concealing stems (at least basally); petals 2-5 mm long (except for 5-10 mm long in B. missouriensis)
                                                              30 Lower cauline leaves pinnatifid or pinnatisect.
                                                                     33 Terminal leaflet lobes nearly entire to crenate or undulate
                                                                     33 Terminal leaflet lobes sharply toothed or cut
                                                                       34 Basal leaves usually withered by flowering; cauline leaf lobes entire to lyrately lobed; usually petals white to pink; [native of riparian habitats]
                                                                       34 Basal leaves usually present at flowering or after; cauline leaves with linear, filiform, lyrate, or runcinate lobes (occasionally unlobed, but if so then leaves usually linear or otherwise thin); petals yellow; [non-natives of various habitats]