Morphological Variation in Populations of Ranunculus repens from the Temporary Limestone Lakes (Turloughs) in the West of Ireland

An unusual form of Ranunculus repens L. occurs in turlough basins (temporary lakes) in the West of Ireland. It is characterized by more highly-dissected and glabrous leaves than the more typical broad-leaved form. Leaf dissection of both forms was quantified using seed-derived plants which were cultivated in standard conditions. Leaves of both forms showed heteroblastic development and became increasingly dissected with each successively produced leaf until the adult leaf shape was attained around leaf 8. The dissection index of adult leaves was genetically based and had a high heritability. Changes in leaf dissection were recorded across a relatively deep, undulating turlough basin. The most dissected leaf form was found deep within the basin among a highly specialized species-poor community which was subjected to the most prolonged period of inundation. An intermediate-leaved form occurred higher up the sides of the basin in a damp grassland community, where the period of inundation was more transient. A broad-leaved form occurred around the upper fringes of the basin among a dry pastureland community. The intermediate-leaved form may have resulted from gene flow between the broad- and dissected-leaved populations, or may have evolved a distinct leaf shape adapted to the prevailing conditions at that point within the basin.