. The Canadian field-naturalist. Figure J. Population of fruiting, ca. 3 m high Marsh Sow-thistle (Sonchus palustris) in cat-tail {Typha spp.) dominated ditch by fen forest (Albion Wetland, Gloucester, September 1993); note 12 cm high drink can at base of tallest plant (centre right) for scale. were any references noted in a survey of appropriate regional, national and continental floristic sources (, Morton and Venn 1990; Scoggan 1979; Kartesz and Kartesz 1980; Fernald 1950). That leads us to conclude that this Ontario record represents the first report of S. palustris for North America.
. The Canadian field-naturalist. Figure J. Population of fruiting, ca. 3 m high Marsh Sow-thistle (Sonchus palustris) in cat-tail {Typha spp.) dominated ditch by fen forest (Albion Wetland, Gloucester, September 1993); note 12 cm high drink can at base of tallest plant (centre right) for scale. were any references noted in a survey of appropriate regional, national and continental floristic sources (, Morton and Venn 1990; Scoggan 1979; Kartesz and Kartesz 1980; Fernald 1950). That leads us to conclude that this Ontario record represents the first report of S. palustris for North America. As S. palustris is not described in North American literature a summary of important differences between it and S. arvensis is provided below (Table 1).. Figure 2. Illustration of key features of Marsh Sow-thisde (Sonchus palustris), right, and Prickly Sow-thistle {Sonchus arvensis), left (from Fitch and Smith 1946). Although the Gloucester, Ontario site contains a number of locally and regionally rare or uncommon introductions (Dugal 1990, 1992) a pattern of occur- rence which might help to explain the presence of S. palustris is not evident. Sonchus palustris is reported to be rare and declining in Great Britain (Hutchison 1955; Fitter and Fitter 1974). While this impHes that the Gloucester, Ontario population more likely has its origin elsewhere in its western Eurasian range (central Europe to Armenia) (Clapham et al. 1987), its origin remains unknown. A survey of the surrounding area east and south of Ottawa in 1992 failed to discover additional popula- tions of S. palustris. Two small additional stands were discovered elsewhere along the edge of the Albion Fen in September 1993; 24 mature plants were observed along the east side of Albion Road 50 m north of Delzotto Road and two inmiature plants were noted 300 m west of Albion Road along Leitrim Road. The disturbed, peaty fen habitat in which all plants were found is rare here and throughout southern Ontario (Dugal 1990; R
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