White campion (white cockle)
Silene latifolia (Melandrium album)

White campion is in the Caryophyllaceae or pink family. It behaves as a biennial or short-lived perennial plant and grows from 1 1 /2 to 3 1 /2 feet tall. Stems are jointed and hairy at the base, but hairless at the tip. Leaves are also hairy, simple, ovate or lanceolate, and originate on opposite sides of the stem. In the spring, perennial plants appear as rosettes and produce flowering stems by mid-May. As the stems elongate, the basal leaves wither. Seedling plants have a taproot that gradually thickens. As plants mature, roots thicken and spread laterally to form short rootstalks. New plants often arise 4 to 8 inches from a mother plant and remain attached by horizontal root segments.
White campion is dioecious, meaning that male and female flowers are borne on different plants. The sex ratio is most often female-biased with male plants ranging from 25–50% of a population. Flowers are white, sometimes pink, with five notched petals. Petals are longer than the calyx. Sepals are fused together to form a sticky tubular calyx surrounding the flower. In male plants, the calyx is 1 /2 to 3 /4 inches long, with 10 veins. In female plants, the calyx is 3 /4 to 1 1 /4 inches long and has 20 veins. Plants will flower from May to September and produce some viable seed within the normal cutting interval of alfalfa and timothy hay. Flowers open in the evening but close by noon. Green seed capsules, if cut from the plant and allowed to dry will often contain viable seeds. Seeds are kidney shaped, grayish-brown to bluish-gray in color, and similar in size to alfalfa or clover seed. The seed surface is covered with pointed tubercles (wart-like projections) arranged in three or four rows on each side, giving the seed a rough appearance. Cotyledons of seedlings are fleshy. First true leaves are covered with short dense hairs. Seedlings are tap-rooted. Root structure changes to a branched system as the plant matures.
Night-flowering catchfly (Silene noctiflora) is often mistaken for white campion. However, night-flowering catchfly, an annual, is a very sticky plant and has perfect flowers, i.e., both male and female structures occur on the same flower on all plants. It also has a simple taproot. Bladder campion (Silene vulgaris) is also similar, but lacks hairs. Its flowers are also perfect. Cow cockle (Vaccaria pyramidata) is an annual, with pink, perfect flowers.