The genus Biscutella (Brassicaceae) is distributed mainly in S. Europe, N. Africa and SW. Asia with around 40 species. The morphologically highly variable, polyploid (2n = 18, 36 or 54) perennial B. laevigata, however, is centred in Central Europe: tetraploids occur in the Alps, while diploids are found in the adjacent regions to the north and east, hexaploids grow in N. Spain. Within B. laevigata around 20 subspecies have been described by different authors. A combined morphometric and nuclear genome size study allows to estimate infraspecific variation and its role in the evolution of this group, with special emphasis on the origin of the polyploids. The morphometric study uses 60 characters including branching pattern, leaf shape, hair-covering and fruit shape. Factor analysis and discriminant analysis show that morphological variation within populations is very high, leading to a much smaller number of subspecies. Nuclear genome size was studied by flow cytometry (propidium iodide staining). Infraspecific genome size variation is of special interest, because there are numerous reports in literature about high variation within species, even related to environmental factors - meaning that genome size would be a doubtful character for taxonomic use. In B. laevigata, the DNA C-values exhibit a very low variation of 1 - 2.5 % (c.v.) within populations and up to 4% between populations. Central European taxa show a basic C-value of 0.94 pg DNA (1C) for the diploids, while the tetraploids have exactly the double value but exhibit a higher variation. For the populations of N. Spain, probably representing another species, the basic C-value is much lower: the diploids have 0.82 pg DNA. An enzyme study presently in progress will help to clear up the relationship between the subspecies. This work was supported by the Austrian National Bank, project 6855.

Key words: Biscutella, Brassicaceae, genome size, infraspecific variation, morphometry, polyploidy