Eryngium planum L.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Perennial to 1 m from a thickened, woody taproot; lvs net-veined, the basal and lower cauline with elliptic-oblong to elliptic-ovate, crenate to spinulose-serrate blade 4–10 cm rounded or cordate at base to the long petiole, the others progressively less petiolate (or sessile), more sharply toothed or cleft, and often broader; heads bluish, ± ovoid, 1.5–2 cm, subtended by spreading, narrow, spinulose-toothed to entire bracts 1.5–3 cm; bractlets firm, 5–6 mm, the lower tricuspidate; 2n=16. Native of Europe, sparingly intr. in fields and waste places, as in N.Y. June, July.
Two other taprooted European spp. are also rarely intr. with us. E. maritimum L. has very firm, broad, palmately veined (and often lobed), very strongly spiny-margined lvs. E. campestre L., also very spiny, has more pinnate and more dissected lvs, the principal ones with a broad, green, spiny-toothed midstrip