Despite its size and the somewhat doubtful mutual relationships, this family is rather uniform and easily recognizable.
Most are herbaceous annuals or perennials, dying off above ground each year. A few species are shrubs or small trees, such as some Acanthophyllum species. Most plants are non-succulent; i.e. having no fleshy stems or leaves. The nodes on the stem are swollen. The leaves are almost always opposite, rarely whorled. The blades are entire, petiolate, and often stipulate. These stipules are not sheath-forming.
The hermaphroditic flowers are terminal, blooming singly or branched or forked in cymes. The inflorescence is usually
dichasial at least in the lower parts, which means that in the axil of each peduncle (primary flower stalk) of the terminal flower in the cyme, two new single-flower branches sprout up on each side of and below the first flower. If the terminal flowers are absent, then this can lead to
monochasia, i.e. a monoparous cyme with a single flower on each axis of the inflorescence. In the extreme, this leads to a single flower, such as in
Githago or Arenaria. The flowers are regular and mostly with five petals and five sepals, but sometimes with four petals. The sepals may be free from one another or united. The petals may be entire, fringed or deeply cleft. The calyx may be cylindrically inflated, as in Silene. The stamens number five or 10 (or more rarely four or eight), and are mostly isomerous with the perianth. The superior gynoecium has two to five carpels (members of a compound pistil) and is syncarpous; i.e. with these carpels united in a compound ovary. This ovary has one chamber inside the ovary. The fruit may be a utricle with a single seed or a capsule containing several seeds.