Intraspecific variation in leaf morphology and anatomy (with special reference to ecotypic differentiation within Geranium sanguineum L., Trollius europaeus L., and Ranunculus acris L.).

(i) Intraspecific variation in leaf morphology and anatomy within Geranium sanguineum, Trollius europaeus and Ranunculus acris has been investigated against a background of the ecological (including edaphic), taxonomic, historical and cytological factors involved in the evolution of each species. Cultivated material, population samples and herbarium specimens have been used. (ii) Genotypically-determined ecoclinal variation in leaf dissection, leaf size, stomatal density and leaf thickness has been found. Leaf dissection increases from oceanic to continental habitats (G.sanguineum, R.acris), from high to low altitudes (T.europaeus, R.acris). Leaf size decreases from shaded to open habitats (G.sanguineum), and with increasing altitude and latitude (T.europaeus, R.acris). Leaf thickness and stomatal density increase from shaded to open habitats (G.sanguineum). (iii) Environmental modification ("reaction pattern") of leaf morphology in G.sanguineum parallels the genotypically-determined variation. (iv) Genotypically-determined variation in height and habit, phenology, pubescence and flower colour has also been investigated. With the exception of flower colour, the variation is shown to be ecologically correlated. (v) The adaptive significance of the observed ecotypic differentiation is discussed at length and compared with information from the fields of morphogenesis, physiognomic plant geography and physiology. Convergence or parallelism in leaf structure at the different evolutionary levels is considered as strongly suggestive of direct survival value. The possible role of genetic assimilation in ecotypic differentiation is discussed. (vi) Experimental evidence is presented which demonstrates the profound influence of leaf shape on the physiological processes of the plant. Gaseous exchange and heat transfer rates are much higher in small and/or narrow leaves. The ecological importance of this is discussed and the observed differentiation of leaf morphology is considered to be directly adaptive.