Eryngium

1. Leaves all netted-veined, of various shape (basal petioled with broad subcordate blades, upper and midcauline nearly sessile and lobed); bracts more than half as long as the head; petals blue; escapes from cultivation.

E. planum

1. Leaves all parallel-veined, simple and elongate (yucca-like); bracts subtending heads less than half their length; petals white; rare native species.

E. yuccifolium