Introduction

The creation of this Checklist of the Vascular Plants of Wisconsin was motivated by an acute awareness by state biologists, wildlife managers, educators, and others for a current, comprehensive, and authoritative listing of vascular plant diversity for the entire state. There are many individuals and organizations statewide and nationwide who require an accurate inventory of the Wisconsin flora for documenting overall biodiversity, rare and endangered species, and other systematic and ecological projects on the plants of Wisconsin. Therefore, the staff at the University of Wisconsin-Madison Herbarium (WIS) have undertaken to produce this Checklist in the hope that it will be useful to the many people wanting information about our flora. It may assist local amateurs in the identification of plants growing in their areas; furnish information which professional botanists can use in phytogeographical studies; document the decline of native plants as well as the spread of adventive and weedy ones; and stimulate interest in the conservation of our native flora.

Although there have been local floras (more recent ones include Eddy, 1996; Hartley, 1960; Judziewicz & Koch, 1993; Lange, 1998; Musselman et al., 1971; Peck & Taylor, 1980; Rill, 1983; Seymour, 1960; and others in manuscript) and treatments of certain plant groups, there has not been a comprehensive checklist for Wisconsin since the one published over a century ago by Swezey (1883). Many families and genera have been treated in the ongoing "Preliminary Reports on the Flora of Wisconsin" series, published between 1929 and 1988 in the Transactions of Wisconsin Academy of Sciences, Arts and Letters. Several book-length treatments of various Wisconsin families or groups have been published as well (Fassett, 1939, 1951; Fuller, 1933; Tryon et al., 1940, 1953; for a complete list of these treatments, see Iltis et al., 1994).

This Checklist provides an authoritative listing of all known native and introduced vascular plants that occur - or once occurred - and reproduce in Wisconsin outside of cultivation. It is based exclusively on herbarium specimens in established collections, a standard that allows individual species records to be verified at any time. Because herbarium specimens from Wisconsin date back to 1811 (Thomas Nuttall's collections along the Wisconsin and Mississippi Rivers as part of the Astoria Expedition), the Checklist includes species that are less common than they once were. Many native species continue to decline, and five species are now believed to be extinct in the wild in Wisconsin. Conversely, non-native species are continually appearing and becoming established in Wisconsin as either naturalized, adventive, or escaped members of the flora; although some may not persist or may remain innocuous, to anticipate any population explosions of these often potentially harmful weeds, it is important to accurately track their presence and spread in the state (Hoffman & Kearns, 1997).

Because the Checklist is a synthesis of the current taxonomic status of the included species, there are likely to be some changes from previous reports. Therefore, we list pertinent synonyms under their accepted names and provide a section of "Excluded Taxa" to call attention to records and reports that are doubtful, incorrect, or unvouchered by herbarium collections. Common names are provided, and special symbols are used for taxa of particular conservation and ecological interest to enhance the usefulness of the Checklist.

The completion of this Checklist represents an important step toward an eventual flora of Wisconsin. The next step toward this goal is to make available detailed distribution maps for all spontaneous vascular plant taxa. By the end of June 1999, in conjunction with the electronic version of this Checklist, we will be posting on the Herbarium’s web site approximately 700 distribution maps for Wisconsin taxa. Within two years we plan to have maps posted for all of the 2,436 native and 792 introduced Wisconsin taxa. With Wisconsin distribution maps thus becoming available, and with other floristic treatments already published, such as Michigan Flora (Voss, 1972, 1985, 1996), Plants of the Chicago Region (Swink & Wilhelm, 1994), and Vascular Plants of Minnesota, a Checklist and Atlas (Ownbey & Morley, 1991), the Upper Midwest is becoming one of the floristically better-known areas of North America.