Integrated Vouchers: A Method Towards Archiving Population-Level Variation in Herbaria

Herbarium specimen use has increased and diversified in recent decades, yet plant collection methods have remained largely unchanged. Here, we describe a new approach for collecting and curating herbarium specimens to more comprehensively document seasonal and population-level variation across phenological, morphological, and life history characteristics of a species. This new specimen model, which we call “integrated vouchers,” combines multiple collection methods, archiving variation across seasons (“phenophase vouchers”), within populations (“mass collections”), and across ontogenetic stages (“life history vouchers”). The method also connects an array of field images and metadata to specimen records through the community science platform iNaturalist. Integrated vouchering requires collecting multiple specimens within the same year and location that are then digitally linked and physically stored together as a unit in a single herbarium folder. We use the Reynoutria Houtt. (Polygonaceae) hybrid species complex as a test case to exemplify the method and describe a new set of integrated vouchers made in southwestern Pennsylvania, U.S.A. Considering herbarium space constraints, time required, and other considerations, integrated vouchers should be viewed as complementing, not replacing, traditional herbarium specimens. This approach provides a standardized framework to document site-specific intraspecific variation and connect other ancillary information rarely found in existing collections. Integrated vouchers implement the emerging “extended specimen” concept in new collections.