This section is from the book "Wild Flowers Of New York", by Homer D. House. Also available from Amazon: Wild Flowers Of New York.
Stems slender, erect, 1 to 2 feet high, simple or branching, from a thick, perennial root, downy-pubescent below, slightly viscid above. Lower and basal leaves spatulate or oblanceolate, 2 to 4 inches long; upper leaves lanceolate or linear-lanceolate, opposite and sessile, the uppermost leaves reduced to small bracts; flowers pink, purplish, blue, or white, three-fourths to 1 inch broad, in many-flowered panicles at the summit of the stems; calyx one-fourth of an inch long, ten-nerved, cylindrical, becoming campanulate in fruit, its apex with five triangular, pointed teeth; petals five, narrowly clawed, the spreading limbs each cleft into four linear lobes, of which the middle pair is longest.
Memoir 15 N. Y. State Museum
Plate 54

A. Cuckoo-Flower; Ragged Robin - Lychnis flos-cuculi
Moist meadows, fields and waste places, New Brunswick to New Jersey and Pennsylvania. Frequent in cultivation. A native of Europe but thoroughly naturalized in many places in the eastern states. Flowering in July and August.
 
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