Genetic variability in Plantago species in relation to their ecology : 4. Ecotypic differentiation in P. major.

Twelve Plantago major plants, good representatives of their populations, appeared to be genetically different for several characters which are important for adaptation to the respective habitat conditions. These characters are: juvenile growth, leaf morphology, production of secondary rosettes, flowering time, seed production, seed size and adult leaf production. The adaptive value of some of these characters was investigated by transplantation experiments in the field and by intraspecific competition experiments. The roadside type of ssp. major was adapted to trampling by being erect and elastic. The lawn type of ssp. major was adapted to a short, frequently cut, vegetation by being prostrate and by producing leaves with short petioles throughout the growth season. In the natural situations in which ssp. pleiosperma occurs, growth rate and first-year seed production of this subspecies were considerably higher than that of ssp. major. In a number of experiments, F1s and F2s were included, derived from crosses between the original plants. The F1s were generally rather well adapted to both parental habitats, whereas the F2s appeared to be less fit. The various alternatives in spending resources relevant for fitness optimization in different habitats are discussed.