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Key to Apiaceae, Key A: Apiaceae with simple leaves

Apiaceae

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1 Leaves linear, lanceolate, or oblanceolate, > 4× as long as wide.
  2 Leaves phyllodial (septate, hollow or flat, segmented); flowers white or purple; [plants of wetlands].
    3 Umbels simple; leaves spatulate, broader towards the tip, often somewhat flattened in ×-section, rounded or obtuse at the apex
    3 Umbels compound; leaves tapering to a pointed tip, either flat or terete in ×-section.
      4 Leaves flat in ×-section, with obvious parallel venation and less obvious septae / cross-partitions
      4 Leaves terete in ×-section, the septae obvious.
        5 Plants 1-11 dm tall, annuals, sometimes mat-forming and adventitiously perennial; fruits 1-3 mm long, with lateral ribs; rays 3-15
        5 Plants 6-24 dm tall, perennials from rhizomes or tubers; fruits 4-9 mm long, with lateral wings; rays 5-20
  2 Leaves “normal” (non-septate, flat, continuous, and in some cases lobed, toothed, or spinose-margined); flowers blue, yellow, white, or whitish-green; [plants of wetlands or uplands].
          6 Flowers borne in involucrate heads; corolla blue or greenish-white
          6 Flowers in compound umbels; corolla yellow or white.
             7 Stem leaves similar to the basal, all simple; corollas yellow; [non-native, of upland disturbed areas]
             7 Stem leaves palmately 3-5-foliolate with linear leaflets, differing from the simple basal leaves; corollas white; [native, of swamps, blackland prairies, and associated disturbed areas, from AL and TN westward]
1 Leaves orbicular, ovate, or elliptic, < 4× as long as wide.
               8 Leaves orbicular, about as wide as, or wider than, long; base peltate or cordate.
                 9 Leaves leathery, with spinose margins; inflorescence a head; flowers blue; [rare introduction]
                 9 Leaves herbaceous or somewhat fleshy. toothed or lobed, but not spinose; inflorescence umbellate or verticillate; flowers white, greenish, or purplish; [collectively common and widespread].
                   10 Foliage and fruits (or ovaries) glabrous; leaves toothed, sometimes also lobed; [common natives and exotics]
               8 Leaves ovate or elliptic, 1.2-4× as wide as long; base cordate, peltate, or truncate.
(c) Fleming, Gary P.
                     11 Leaves perfoliate; flowers yellow; [rare exotics].
                     11 Leaves cordate or truncate at the base; flowers white, green, yellow, blue, or purple;
                          13 Flowers greenish or blue; leaves all simple (sometimes stem leaves lobed); inflorescence a head or very congested (subcapitate) umbel; [plants of wetland situations, prostrate, creeping, or erect].
                            14 Inflorescence a very congested (subcapitate) umbel, with 4-9 flowers; leaves cordate at the base, long-petiolate, the petioles characteristically 2× as long as the leaf
                            14 Inflorescence a head, with > 20 flowers; leaves cuneate to truncate at the base, sessile to short petiolate, the petioles < 1× as long as the leaf (except E. prostratum)
                          13 Flowers yellow or purple; basal leaves simple, stem leaves usually compound; Inflorescence a compound umbel; [erect plants of upland situations].
                              15 Fruits (partly to fully mature) with thin-edged wings; flowers yellow or purple; central flower of each umbellet staminate and pedicelled; fruits all pedicelled in all umbellets
                              15 Fruits ribbed (with rounded, cordlike ribs), lacking thin-edged wings; flowers yellow; central flower of each umbellet either staminate and pedicelled, or pistillate and sessile; fruits all pedicelled in some umbellets (those with a staminate central flower), or the central fruit sessile in some umbellets (those with a pistillate central flower)
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Key to Apiaceae, Key C: Apiaceae with 1-pinnate leaves

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1 Larger leaves 20-50 cm wide, 3 (-5) foliolate, many of the leaflets deeply lobed into segments often > 10 cm wide; fruits 8-15 mm long, pubescent; petioles sheathing and also strongly dilated
1 Larger leaves 3-25 cm wide, 5-15 (or more) foliolate, the leaflets variously toothed, if also deeply lobed, the segments < 3 cm wide; fruits 1-7 mm wide; petioles sheathing, not dilated.
  2 Leaves septate (phyllodial), the lateral leaflets attached at septae
  2 Leaves non-septate, non-phyllodial.
    3 Leaflets entire or with a few teeth (rarely as many as 7 on each side), these usually near the midpoint of the leaflet; fruits 4-7 mm long; corolla white
    3 Leaflets rather finely toothed (and sometimes also deeply lobed), the teeth evenly disposed along the margins; fruits 1-6 mm long; corolla white or yellow.
      4 Corolla yellow; fruits 5-6 mm long; longer rays in each compound umbel > 5 cm long
      4 Corolla white or pink; fruits 1-5 mm long; longer rays in each compound umbel < 4 cm long.
        5 Leaflets obtuse to broadly rounded, < 1.5× as long as wide; upper leaves often dramatically more dissected (i.e., bipinnate) and with narrower leaflets or segments than the basal and lower leaves; [plants of disturbed upland situations].
          6 Bracteoles present subtending the umbellets; outer flowers of the umbellet asymmetric, with the outer petals larger and often bifid (raylike); annuals; stems solid
          6 Bracteoles absent; all flowers radially symmetrical; biennials or perennials; stems hollow or solid
        5 Leaflets acute to acuminate at the apex, > 1.5× as long as wide; upper leaves similar to the basal in shape and degree of dissection, smaller or with fewer leaflets if they differ at all; [plants of wetlands].
             7 Umbels on stout peduncles 4-10 cm long; leaf margins sharply serrate; highly dissected submersed leaves sometimes present (submersed leaves also occasionally simple)
               8 Basal leaves usually many, mildly carrot-scented; mericarp ribs filiform, oil ducts 14 on abaxial face, 3 on commissure; [rare in c. TX]
               8 Basal leaves 1 or 2, not aromatic; mericarp ribs corky-thickened, oil ducts 1-3 in intervals, 2-6 on commissure; [east and north of c. TX].