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Click the number at the start of a key lead to highlight both that lead and its corresponding lead. Click again to show only the two highlighted leads. Click a third time to return to the full key with the selected leads still highlighted.

Key to Eryngium

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1 Inflorescence unbranched, the heads solitary on peduncles from the leaf axils of the prostrate to erect stem.
  2 Leaves pinnately lobed or dissected
  2 Leaves entire, irregularly toothed (rarely with some minor, irregular lobing).
    3 Heads subglobose or hemispherical when fully developed, about as wide as long; bracts subtending the head barely extending beyond the base of the head; main stems leaves linear, narrowly elliptic, narrowly oblanceolate, sometime tricuspid apically
    3 Heads cylindrical, longer than wide; bracts subtending the head longer than the radius of the head, thus extending conspicuously beyond the base of the head; main stem leaves elliptic, broader than above
1 Inflorescence branched, the heads in a cyme borne terminally on the erect or prostrate stem.
      4 Basal and cauline leaves unlobed (except sometimes the uppermost; note that bracts in the inflorescence are often lobed), 3-100 cm long; leaf margins without coarse spine-tips (finely spinulose in E. foetidum).
        5 Basal leaves evenly and rather finely toothed with spine-tipped teeth
        5 Basal leaves with entire or crenate margins, lacking spiny tips (though in some species with flexible bristles along the margins).
          6 Blades of basal and lower cauline leaves 3-7 (-10) cm long, acute to obtuse apically, cordate to truncate basally, with a length/width ratio of 1.5-3 (-6)
             7 Head hemispheric, about as wide as high; [native, seeps, bogs, and wet pine savannas, VA, KY, AR, and OK southwards]
             7 Head ovoid, taller then wide; [non-native from horticultural use]
          6 Blades of basal and lower cauline leaves 10-100 cm long, acuminate to acute apically, clasping basally, with a length/width ratio of 5-50.
               8 Leaves with primary veins pinnate-reticulate, with or without marginal bristles; flowers blue.
                 9 Styles 3.0-4.0 mm long at maturity, scarcely exceeding the bractlets (which subtend each flower); heads subglobose to hemispherical, 6-12 mm in diameter; middle cusp of the bractlets elongate, distinctly longer than the lateral cusps
                 9 Styles 4.0-6.0 mm long at maturity, exceeding the bractlets; heads globose, 9-15 mm in diameter; middle cusp of the bractlets about equal in length to the lateral cusps
               8 Leaves with primary veins parallel, with marginal bristles; flowers greenish-white.
                   10 Larger leaves < 1.5 cm wide; marginal bristles in fascicles of 1-3 (-4), those on the lower portion of the leaf usually in fascicles of 2-3
                   10 Larger leaves > 1.5 cm wide; marginal bristles of leaves solitary
                     11 Plant green; marginal bristles triangular (broadened at the base); flowering late
                     11 Plant glaucous; marginal bristles acicular; flowering early
      4 Basal and cauline leaves (all, or at least many of the cauline) definitely deeply lobed into 3 or more divisions, < 10 cm long; leaf lobes tipped with moderately stiff to very stiff spine tips.
                       12 Leaves thickly coriaceous, glaucous blue, palmately lobed, about as wide as long
                       12 Leaves herbaceous to stiff, green to slightly glaucous, pinnately toothed or lobed.
                          13 Heads blue; basal leaves serrate but not divided.
                            14 Heads 20-35 mm tall, purple to reddish; heads capped with conspicuous (1-2 cm long) spinescent bracts
                            14 Heads 4-15 mm tall, bluish to purplish; heads capped with a few, mostly entire, spinescent bracts, or lacking them.
                              15 Plants erect, stem solitary, branching upwards; fruits 1-2 mm long
                              15 Plants diffuse, decumbent, branched from the base and upwards; fruits 1.5-3 mm long
                                16 Cauline tips absent; mericarps 1.5-2 mm long
                                16 Cauline leaves present, spine tipped; mericarps 2.5-3 mm long
                          13 Heads greenish, whitish, or pale lavender; basal leaves pinnately or pinnately-ternately divided.
                                  17 Plants stout, fleshy, usually glaucescent; basal leaves 10-25 cm long and wide, pinnately or pinnate-ternately divided into > 7 segments, the cauline leaves similar but reduced in size and number of divisions; heads 10-15 mm in diameter; [rare ballast waif of disturbed ground]; [subgenus Eryngium]
                                  17 Plants slender, not fleshy, green; basal and cauline leaves 2-6 cm long, 3-5 (-7) pinnately parted; heads 5-8 mm in diameter; [native species of dry pinelands or scrub of the Coastal Plain of e. GA, s. AL, and FL].
                                    18 Basal leaves pinnately lobed; stems decumbent at base, ascending (the mature plant often wider than it is tall); stems leafy throughout their length, usually with 10 or more leaves; [dry pinelands and scrub of the Coastal Plain of e. GA, s. AL, and FL]
                                    18 Basal leaves trilobed; stems ascending at base (the mature plant taller than wide); stems erect, unbranched; stems sparsely leafy, especially upwards, usually with 7 or fewer leaves; [endemic in Florida scrub in Highlands County, c. peninsular FL]
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