A foliar morphometric approach to the study of salicaceae

An assemblage of leaves of four species of willows (Salix viminalis, S. alb a, S. fragilis, and S. caprea), two of their hybrids (S. alba x fragilis an d S. caprea x viminalis), two species of poplars (Populus alba and P. tremu la), and two "external" species (Elaeagnus angustifolia and Pyrus salicifol ia) was analyzed. The study was designed to determine whether leaves that a re very close in shape but belong to different species, particularly the el ongated leaves of S. viminalis, S. alba, S. fragilis, E. angustifolia, and P. salicifolia, could be discriminated by continuous foliar characters (tha t is, vegetative characters), despite both the great foliar polymorphism me t in Salicaceae (especially in the genus Populus) and hybridization problem s. Our results show that multivariate analyses (principal component analysi s [PCA] and cluster analysis) of an appropriate character set enable leaves to be classified in their own species at more than 98 %, even in these dif ficult conditions. It can be seen from this work that PCA is a good tool wh en it keeps a maximum of total variability; that is, when there are few tax a; on the other hand, cluster analysis is more appropriate with many taxa. One can then envisage the application of this morphometric approach to foss il-imprint determination, in which even fragmentary paleobotanical remains could be included. This would give access to real biodiversity of tertiary flora and to intraspecific variability.