The effects of competition on growth and form in Glechoma hederacea

Morphological responses to competition were analysed in Glechoma hederacea, a clonal herb with plagiotropic shoots. Ramets of clones were grown either in isolation or in competition with cut or uncut Lolium perenne swards. G. hederacea produced the same above ground biomass, but different morphologies when grown with short and tall grass. Despite considerable reductions in biomass and stolen branching when grown with competition rather than in isolation, the capacity for lateral extension of primary stolons was maintained. All other measured variables were reduced by competition, except for stolen internode length and petiole length and mass. These variables reached their greatest values in the uncut grass treatments. These responses could promote avoidance of competition by escape in both the horizontal and vertical planes; growth through vegetated sites would be rapid, and sites where competitors are absent would be occupied more densely. Reductions in PAR and in the R/FR ratio incident on the plant are both implicated in inducing these morphological changes. Differences in relative humidity, caused by the proximity of neighbours, also appeared to exert a considerable influence upon growth and morphology of G. hederacea. Connected parts of G. hederacea clones grown with and without competition developed different morphologies; each primary stolen behaved as an integrated physiological unit, developing a morphology appropriate for the conditions in which it was growing.