This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Annual or perennial, diffuse or erect, branching mostly glabrous herbs, with opposite or verticillate (rarely alternate) sessile or short-petioled leaves, entire or nearly so, and small axillary peduncled red blue white or pink flowers. Calyx 5-parted, the lobes lanceolate or subulate, spreading, persistent. Corolla deeply 5-parted, rotate, the segments entire or erose, convolute in the bud, longer than the calyx. Stamens 5, inserted at the base of the corolla, filaments subulate, or filiform, puberulent, or pubescent, distinct, or united into a narrow ring at the base; anthers oblong, obtuse. Ovary globose, ovules numerous; stigma obtuse. Capsule globose, circumscissile, many-seeded. Seeds minute, flat on the back. [Greek, delightful.]
Annual, diffuse, usually much branched; branches 4'-12' long, 4-sided. Leaves ovate or oval, membranous, opposite or rarely in 3's, sessile or somewhat clasping, obtuse or acutish, 3"-10" long, black-dotted beneath; peduncles filiform, 1/2'-1 1/2' long, recurved in fruit; calyx-lobes keeled, rather rigid, slightly shorter than the crenate glandular-ciliate or glabrous corolla-segments; flowers scarlet or blue, sometimes white, usually with a darker center, 2"-3" broad, opening only in bright weather; capsule glabrous, about 2" in diameter.
In waste places, Newfoundland to Florida, west to Minnesota, Texas and Mexico, and on the Pacific Coast. Naturalized from Europe. Red chickweed. Burnet-rose. Shepherd's-clock. Bird's-eye or-tongue. Sunflower. Eyebright. Wink-a-peep. Shepherd's-delight. May-Aug.