They are mostly herbaceous plants, either annual or perennial; a few are subshrubs. The leaves are mostly opposite or whorled, alternate in a few species, simple, and ovate to lanceolate in shape. The flowers have four petals often notched. These are usually smallish and pink in most species, but red, orange or yellow in a few, and large and bright magenta in the Chamerion group. The fruit is a slender cylindrical capsule containing numerous seeds embedded in fine, soft silky fluff which disperses the seeds very effectively in the wind.