THE GENECOLOGY OF LAWN WEEDS. V. THE ADAPTIVE SIGNIFICANCE OF DIFFERENT GROWTH HABIT IN LAWN AND ROADSIDE POPULATIONS OF PLANTAGO MAJOR L.

Abstract

SUMMARYThe differential responses of two genetically‐determined growth forms of Plantago major L. ‐prostrate plants from lawns and erect plants from roadsides ‐ were studied in experiments involving clipping and reciprocal transplants.Under a regime of clipping at 2 cm above soil level in a pot experiment, plants from roadsides were severely damaged and all reproductive structures were lost, whereas plants from lawns were able to produce several thousand seeds per plant. In a reciprocal transplant experiment of ‘mown’ and ‘tall grass’ plots, a small number of erect inflorescences of the roadside plants survived mowing and were able to produce a minute quantity of seed. Lawn plants in mown plots produced significantly more seeds. In the tall grass plots, the roadside plants exhibited significantly greater vegetative and reproductive dry wt than lawn plants.Estimates of coefficients of selection were calculated for both experiments. Although values varied with different estimates of performance, in general: (1) selection against the roadside plants in the clipping treatment of the pot experiment and in the mown plots of the reciprocal transplant experiment was high (c.s. values based on reproductive features ranged from 078 to 1 00); and (2) coefficients of selection against lawn plants in the control of the pot experiment and in the tall grass plots of the reciprocal transplant experiment were also high (c.s. values in the reciprocal transplant experiment ranged from 0‐74 to 0‐77).Plants from lawns flowered significantly earlier than those from roadsides, and both lawn and roadside plants flowered significantly later in tall grass plots than in mown plots.Some problems and advantages of reciprocal transplant experiments are discussed.Our experiments provide strong evidence that differences in growth habit in Plantago major are of adaptive significance.