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The Red Lake Peatland, situated in N-central Minnesota, is the largest continuous mire in the northern portion of the contiguous United States. It consists of a mixture of ombrotrophic bogs and minerotrophic fens organized into a complex of highly distinctive landforms, including open bogs, wooded bogs, Sphagnum lawns, strings, flarks, fen-pools and wooded islands. The bogs are poor in species and occupy acid sites with water poor in mineral salts; the minerotrophic areas are floristically richer and can be divided into poor-and rich-fen sites. Ditching and roadbuilding in certain portions of the peatland have produced drastic changes in the vegetation and landscape as a result of obstructed water tracks flooding upstream and drying out downstream. The peatland, which occupies a large area of gentle slope and poor drainage, has a flora that is relatively impoverished. In all, 331 plant taxa were recorded from the mire, including 195 vascular plants, 67 bryophytes and 69 lichen taxa. Members of the Cyperaceae account for 23 % of the vascular flora, and the largest genus in the mire is Carex with 29 species. Each landform feature is distinctive in its floristic composition, and the vascular and nonvascular taxa associated with the different physiographic features are discussed. This paper provides an account of Carex in the peatland and discusses the differential response by members of the genus to gradients of nutrition, shading and hydrology. Some carices grow best under acid conditions, thus frequenting ombrotrophic and poor-fen sites, whereas other species grow best in rich-fen sites. Carex species useful in separating areas of ombrotrophy from those of poor fen are indicated, as are those carices that serve as obligate rich-fen indicators. The floristic similarities between the Red Lake Peatland and 14 other peatlands in North America and northern Europe are discussed, and the ombrotrophic bog flora of the Red Lake Peatland is compared to the bog floras of the Hudson Bay lowlands and northern Fennoscandia.

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1992. A major floristic boundary in Minnesota: an analysis of 280 taxa occurring in the western and southern portions of the state. Can. J. Bot. 70: 319-333. A prominent floristic boundary is identified by combining distribution maps based on herbarium records of 280 taxa that occu; in western and southern Minnesota. A set of b o u n d a j dots was plotted for each taxon with the help of a grid overlay, and the coordinates of the dots in the set were tabulated and mapped by computer. The map shows a band of concentration of species limits that runs roughly north-south in the west and bends eastward in the central and eastern parts of the state. When subsets of the 280 taxa based on habitat preference are mapped independently, the band remains distinct. Single factors of climate and landscape alone are inadequate to explain the position and strength of the floristic boundary. The next most simple hypothesis proposes that the boundary results from an abrupt change in ecosystem type, from a woodland kept open by the interaction of fire with vegetation, topography, and soils to a closed forest where fire was less frequent. The concentration of limits implies that for many species migration had reached an equilibrium with ecosystem factors under the present climate. . 1992. A major floristic boundary in Minnesota: an analysis of 280 taxa occurring in the western and southern portions of the state. Can. J. Bot. 70 : 319-333. En combinant les cartes de distribution et les donnCe d'herbier de 280 taxa du sud et de l'ouest du Minnesota, les auteurs ont identifie une importante frontibre floristique. Une frontibre en pointillCs B CtC enregistree pour chaque taxon en superposant une grille, et les coordonnCes des points ainsi obtenues ont CtC tabulees et cartographiees par ordinateur. Les cartes montrent une bande de concentration de limites d'espbces qui coure gCnCralement du sud au nord dans la partie ouest et gagne vers l'est dans la partie centrale et vers l'est de 1'Ctat. Lorsque des sous-ensembles de ces 280 taxa sont cartographiks indkpendamment en se basant sur I'habitat, ces bandes demeurent distinctes. Les facteurs du climat pris un B un et le paysage seul ne peuvent expliquer la position et la force de cette frontibre floristique.L'hypothbse suivante, la plus simple, serait que la frontibre rCsulte d'un changement abrupte dans le type d'Ccosystbme, allant d'une forkt maintenue ouverte par les interactions du feu avec la vCgCtation, la topographie, et les sols, B une forkt oh l'incendie est moins frCquent. La concentration des limites implique que pour plusieurs espbces la migration a atteint un tquilibre avec les facteurs CcosystCmique, sous le climat actuel.

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