Weed Research. 1995. Volume 35. 141-148 Clonal growth and fragment regeneration of Rumex obtusifolius L. J. PINO,* R. J. HAGGAR, F. X. SANS,* R. M. MASALLES* AND R. N. SACKVILLE HAMILTON BBSRC Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth, Dyfed, SY23 3EB UK, and *Departamento de Biologia Vegetal, Universitat de Barcelona, Barcelona, Spain Received 1 December 1993 Revised version accepted 11 March 1994 Summary Clonal growth and fragment regeneration of Rumex obtusifolius L. were analysed in two dif- ferent studies. Clonal growth system was des- cribed by a morphological study of underground structure of different-aged individuals, using maximal branching order in the stem system as an age estimator. Glasshouse experiments were conducted, testing the regenerative capacity of different below-ground parts and the estab- lishment of above root-collar fragments planted at different depths under contrasting water regimes. Results showed the presence of a 'phalanx' type clonal growth system in grassland populations of Rumex. The main structure in- volved in clonal growth proved to be the stem system; the region above the root collar was also the only part able to regrow after damage. Stem fragment regeneration occurred to depths of 15 cm, but was prevented in soils maintained at waterlogging and field capacity. The significance of these results in relation to nonchemical con- trol of Rumex populations in grasslands is discussed. Introduction Broad-leaved dock (Rumex obtusifolius L.) is one of the most troublesome of grassland weeds, especially in intensively managed grasslands (Haggar, 1980; Hongo, 1986). In a nationwide survey of Rumex incidence in UK grasslands, Haggar (1980) found that infestations are en- couraged by slurry and nitrogen applications, which increase soil fertility, and by low sward density resulting from cutting for silage and soil disturbances. The species can be considered as a noxious weed because it is able to decrease grass herbage (Oswald & Haggar, 1983; Courtney, 1985). Long-term control of dock by herbicide application h'as proved variable in effectiveness (Savory & Soper, 1970; Speight & Whittaker, 1987). Seed output is considered the main regenera- tive system of the species. Large mature plants can produce ripe seeds twice during a growing season, totalling some 60000 seeds per year (Cavers & Harper, 1964; Foster, 1989). More- over, seeds can remain viable for several years when buried deeply in soil (Cavers & Harper, 1964) and germinate rapidly after soil disturb- ance (Weaver & Cavers, 1979; Roberts & Totterdell, 1981). In dense swards, however, seedlings seldom establish, and are restricted to bare soil gaps (Cavers & Harper, 1967). Vegetative regeneration plays a minor role in Rumex establishment. The species does not appear to have a true clonal growth mechanism, common in grassland species, although under- ground system fragments produced in field operations such as ploughing or rotavating are able to regenerate new individuals (Cavers & Harper, 1964; Hongo, 1989). Data on the re- generative capacity of different parts of sub- terranean structure are, however, unclear as a result of the confusion existing in the distinction ® 1995 European Weed Research Society