Rumex

Tutin, T. G., Heywood, V. H., Burges, N. A., Moore, D. M., Valentine, D. H., Walters, S. M. & Webb, D. A., 1964, Flora Europaea - Volume 1. Lycopodiaceae to Platanaceae, Cambridge University Press : 85

Subgen. Rumex (Subgen. Lapathum ). All or most flowers hermaphrodite. Valve several times as wide as the nut, with or without tubercles. Basal and lower cauline leaves never hastate or sagittate.

Many species of Subgen. Rumex hybridize freely. Most hybrids are highly sterile, the pollen grains being of irregular size or remaining clumped together in the anthers. Hybrids may be recognized by the lax and untidy habit, the stems often taller than their parents, the mostly sterile flowers shed prematurely from the primary inflorescence, the occurrence of secondary flowering branches below the primary inflorescence, the valves of different shape and sizes on the same plant, and the nuts empty or failing to develop.