Wood-poppy (Stylophorum diphyllum) COSEWIC assessment and status report: chapter 4

• Previous page
• Table of contents
• Next page

Distribution

Global range 

Stylophorum diphyllum is restricted to eastern North America. A general distribution map is given in Figure 2.

Figure 2. Global distribution of Stylophorum diphyllum.

This map is based on distribution information provided by individual state authorities and other records from herbarium specimens and the literature (Bowles and Oldham, 1993). Fernald (1950) gives the range as western Pennsylvania to Wisconsin, south to southwestern Virginia, Tennessee and Missouri, but no herbarium records exist confirming the existence of Stylophorum diphyllum in Wisconsin (Wisconsin SH, 2006). The inclusion of Pennsylvania in the range appears to be based on a single specimen, probably from western Pennsylvania, but lacking precise location information, and on unconfirmed reports of the species in Allegheny County (Buker and Thompson, 1986). Three locations of the species are currently known for Pennsylvania, but none are in natural settings and Buker and Thompson (1986) could not confirm its current or historical native occurrence there.

Canadian range 

Stylophorum diphyllum is known from three extant locations near London, Ontario at the northern limit of the Eastern Deciduous Forest Region or Carolinian Zone in Ontario (Figure 3).

Figure 3. Distribution of Stylophorum diphyllum in Ontario.

It appears always to have been very rare in Canada. All historic records are from the same region. The Canadian range makes up less than 1% of the global distribution.

Only four historic collections are known. The three extant populations (Ilderton, Fanshawe, London) are from near Plover Mills, Middlesex County. For one of the historic records, the only locality given is "Thames River". Because of the vague locality information given for these historic records, it is uncertain as to which, if any, of the extant populations these refer to. Until 1987 no collections had been made since 1889. Keddy (1987) assumed the species to be extirpated from Ontario. Phipps (pers. comm. 1993) reported seeing a small clump of Stylophorum diphyllumwith flowers near Ilderton, Ontario, in 1972. Dufton (pers. comm. 1993) photographed a population near Fanshawe, Ontario, also in the early 1970s. A copy of this photograph is deposited in the University of Western Ontario (UWO) Herbarium. In 1987,Stylophorum diphyllum was discovered by David Stephenson on a small tributary of the Thames River near London, Ontario (Stephenson, 1987). In 1994 the senior author and Marjory Dufton rediscovered the population near Fanshawe, and in 1996 the senior author and James Phipps rediscovered the population near Ilderton.

The Extent of Occurrence (EO) in Ontario was calculated by drawing a perimeter connecting the three sites and calculating the area using a Geographic Information System (GIS) computer program. The EO is about 150 km². The total area actually occupied by the populations, calculated by drawing a perimeter line around each population mapped into GIS, is <1 ha., with the three sites contributing 0.48 ha, 0.45 ha and 19.5 m². Using a 1 km² grid overlay, the Area of Occupancy (AO), based on COSEWIC criteria, would occupy 3 km² and based on a 2x2 km grid would occupy 12 km².