Pollen grains are considered to be species specific. Therefore, they can be used to establish phylogenetic relationships among plant taxa and to identify source plants during the analysis of palynological samples, e.g., air (aeropalynology) or honey (melissopalynology). To fully develop this potential, a large reference pollen collection is essential and enables palynologists to expand their expertise. Moreover, because the identity of reference pollen depends upon the plant from which the pollen was obtained, that plant must be accurately identified and preserved as a voucher specimen.
Ideally, a pollen grain description or identification for a taxon should be based upon several pollen samples taken from voucher plants collected across a wide geographical range. In addition, the pollen samples should represent different years and should be prepared by using different techniques. Although a pollen description or identification can be determined from a single specimen, the result is often of limited value because of the possible variation within the taxon. The probability of proper identification of pollen grains becomes greater as the maintenance and expansion of the reference collection increases.
Few palynological texts or atlases explain how to collect voucher plants or how to remove and preserve polleniferous material from either a fresh or dried plant. Both processes are essential to the production of a pollen reference slide and micrograph collection. Wodehouse (1965) suggested collecting pollen from the first open flowers and recommended collecting pollen from taxa that are allowed to shed their pollen indoors. With this method, take care to prevent contamination of other taxa and the work area.
Traverse (1965) suggested collecting polleniferous material from herbarium specimens. With this technique, flower buds at the time of opening (anthesis) are preferred. Traverse recommended using unopened pollen-producing structures for the study of amentiferous trees (those with catkins) or gymnosperms.
Ogden et al. (1974) briefly described the preparation and storage of pollen packets and also briefly discussed the collection and preparation of herbarium specimens. Likewise, Faegri et al. (1989) discussed the merits and proper maintenance of a pollen reference collection. Although neither author expounded on acquisition of polleniferous material, they described several preparation techniques and different mounting media for slide preparation.
A voucher plant specimen is a plant that has been collected, identified, and permanently stored in an herbarium. Vouchers must be retained for a reference pollen slide collection because these specimens allow research on both the plant and its pollen to be verified and repeated. Voucher specimens enable a researcher to re-examine the preserved plant material and reprocess and re-examine the pollen grains taken from the specimen.