. The Canadian field-naturalist. 354 The Canadian Field-Naturalist Vol. 91 frequent and, in fact, a serious weed of cornfields in the extreme southwest. Its weedy nature has been documented by Alex and Switzer (1976). Panicum dichotomiflorum, or at least this ecotype (which may be of recent origin), is a tough plant tolerant of extremely dry, exposed habitats with levels of certain metals in the soil that would be toxic to many plants. Not surprisingly h appears to be spreading. Most of the specimens cited above may be clearly segregated as var. geniculatum (Wood) Fern. Panicum rigidulum Nees
. The Canadian field-naturalist. 354 The Canadian Field-Naturalist Vol. 91 frequent and, in fact, a serious weed of cornfields in the extreme southwest. Its weedy nature has been documented by Alex and Switzer (1976). Panicum dichotomiflorum, or at least this ecotype (which may be of recent origin), is a tough plant tolerant of extremely dry, exposed habitats with levels of certain metals in the soil that would be toxic to many plants. Not surprisingly h appears to be spreading. Most of the specimens cited above may be clearly segregated as var. geniculatum (Wood) Fern. Panicum rigidulum Nees Hastings County: about 1 mi ( km)south of Stoco. W. G. Dore 13490, 15 August 1951. (sub. P. agros- toides) (DAO). On shore of Moira River at the bridge, Stoco. W. G. Dore 13493, 15 August 1951 (sub. P. agrostoides) (DAO). Wet rocky flood-shore of bay of Stoco Lake, Tweed. W. G. Dore 13496, 15 August 1951 (sub. P. agrostoides) (DAO). Muskoka District: Wood township, Concession VI, Lot 37, Hurling Point, 1 mi ( km) west of Bala. R. E. Whiting, L. Jewitt 1437, 23 August 1972 (sub. P. agrostoides) (herb. R. E. Whiting, TRT)* Morrison township, VIII-31, northeastern shore of Sparrow Lake, km west southwest of Kilworthy Station. A. A. Reznicek, R. Bobbette 2391, 1 Sept- ember 1975 (herb. R. E. Whiting, TRT). This very rare species is apparently native on rocky shores near the southern edge of the Canadian Shield (Figure 1). The two recent Muskoka collections are both from crevices in Precambrian rock directly on the shores of lakes. They were not widely separated and the species is likely scattered on other, similar shores in this region. The plant is reported by Stroud (1941) from Wellington County, Ontario, apparently based on a specimen alleged to be from Guelph: "meadows and pastures, Guelph, Ontario, L. McDougall, July 1937" (DAO). It is very likely that the specimen has been mislabelled as per annotations on the sheet by W. G. Dore and B. Boivin. Panicum rig
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