Open-pollinated seed was collected from several seed parents in each of 16 British populations of Rumex crispus L., representing the three principal variants of this species. Progeny of these seed parents (family lines) were grown in a garden trial, which revealed statistically significant differences between and within the populations sampled.
(1) Coastal plants had denser inflorescences, fewer flowering stems, later anthesis and a greater development of corky perianth tubercles than inland plants.
(2) Plants from riverine tidal mud at Tintern were distinct in their exceptional height, more or less uncrisped leaves, lax inflorescences, very early flowering and tubercle pattern intermediate to coastal and inland plants.
(3) There was considerable variation between populations within coastal and inland habitats and within family lines. This spectrum of variation suggested that both outbreeding and inbreeding might occur in R. crispus.
(4) Many plants from inland populations, with the exception of those from Tintern, flowered in their first year of growth, whereas populations from coastal areas and Tintern flowered in their second (or a later) year of growth.
(5) There was evidence of gene flow between coastal and inland variants of R. crispus at ‘points of contact’, especially where coastal habitats had been disturbed. Plants from a few inland sites appeared to be hybrids between R. crispus and R. obtusifolius.
(6) In cultivation, inland populations flowered consistently earlier than coastal plants. A similar difference in flowering time was recorded in a field study of a coastal area of Suffolk.