Perennial forest herbs with sympodial fibrous or woody rhizomes and aerial stems bearing distichously arranged leaf sheaths or foliage leaves, both kinds eligulate, each stem ending in an ‘inflorescence’ (the synflorescence of Andersson, 1976). This is a compound bracteate cyme (synflorescence) with fragile flowers in pairs. This is a mainly New World family, with relatively few species in Africa, Asia and the Pacific area.

The leaves have open sheaths ± a false petiole, but always with a pulvinus (calloused portion) next to the leaf blade. In Megaphrynium and Thaumatococcus the pulvinus is particularly long, about 10 cm. The leaf blade is entire, ± ovate-elliptic and asymmetrical, one margin being ± parallel to the midrib, the other curved. Venation is close and pinnate, cf. Chapter 33, Zingiberaceae. In the bud, the straight-edged leaf half is rolled round the other half (ptyxis supervolute). Usually, corresponding halves of the leaf blade are either straight or curved (homotropy, Trachyphrynium), but occasionally leaves on one side of the stem will show symmetry consistently opposite to that of leaves on the other side (anitropy, Marantochloa congensis).

The aerial stems appear forked, often in a zig-zag way, but bear true lateral branches. Each branch bears a two-keeled prophyll (scale) as its first leaf on the adaxial side.

Various developmental patterns exist in the family, according to the relative development of aerial stems and petioles.