The purpose of this project is to compile morphological, ecological and taxonomic information on worldwide, contemporary Salix to better recognize and interpret fossil remains of that genus. Leaves from 52 species of all four subgenera and from 36 sections were cleared, stained and scanned on a high-resolution flatbed scanner. These specimens, together with extensive herbarium material, were examined, and classified by overall shape, form of leaf base and apex, venation patterns, and epidermal and marginal traits. The modern genus includes a much broader spectrum of leaf forms than is widely recognized as "typical". Some broad-leaved species occur in riparian habitats, together with narrow willow-like forms. Nanophyllic and leptophyllic taxa grow in high mountain habitats and are usually only found in Quaternary deposits. Venation is pinnate camptodromous (eucamptodromous with a varying tendency towards brochidodromous loops) in the vast majority of species. Several members of subgenus Chamaetia show a more scale-like venation with three or more strong secondaries emerging from the petiole. "Willow-like" leaves are found in numerous families from tropical to alpine or arctic habitats; for extra-generic demarcation, leaf shape, venation pattern, leaf base, characteristics of the margin (salicoid teeth, presence or absence of a fimbrial vein) and epidermal traits are the most important criteria. For infra-generic classification, leaf shape, secondary vein patterns, and margin characteristics are used. Marginal teeth and glands vary considerably in size, shape, and frequency within the genus and are therefore important tools in paleobotanical taxonomy. This study is part of a larger project which will include 1) an examination of fossil and modern pollen, and modern stipules, inflorescences, and infructescences, and 2) a worldwide classification of the contemporary genus (G. Argus).

Key words: fossil, salicoid teeth, Salix, worldwide classification.