BUECHLER, WALTER K.1* and GEORGE W. ARGUS2. 11408 Shoshone Street, Boise, ID 83705; 2R.R.3-310 Haskins Rd., Merrickville, Ontario, Canada K0G 1N0. - Is this a willow leaf? - A review of diagnostic traits in modern Salix (Salicaceae) for use in fossil identification.
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.