33. Ptilimnium Raf. (mock bishop’s weed)

(Easterly, 1957)

Plants annual, glabrous. Stems erect or ascending. Leaves alternate (basal leaves usually absent at flowering), short-petiolate or more commonly sessile, the sheathing bases not or only slightly inflated. Leaf blades narrowly ovate to oblong-ovate in outline, pinnately 2–3 times dissected, the usually numerous ultimate segments narrowly linear, usually threadlike. Inflorescences terminal and axillary, compound umbels, short- to more commonly long-stalked. Involucre of few to several bracts. Rays 4–25. Involucel of 2–5(–7) bractlets, these mostly shorter than the flower stalks, linear. Flowers 5 to numerous in each umbellet. Sepals minute, narrowly to broadly triangular scales. Petals obovate, often appearing shallowly notched, but narrowed or tapered abruptly to a short, slender tip, white. Ovaries glabrous. Fruits broadly ovate to nearly circular in outline, slightly flattened laterally, glabrous, the mericarps with the 5 ribs rounded. Four species, eastern and central U.S.