Eastern prairie fringed-orchid COSEWIC assessment and status report: chapter 6

Distribution

Global Range

The Eastern Prairie Fringed-orchid once occurred from Maine west to southern Ontario and Michigan, southern Wisconsin, southeastern Iowa and south to Oklahoma, Louisiana and Arkansas (Sheviak 1987), east to central Virginia and Pennsylvania with a higher concentration of occurrences (many extirpated) in the area of the southern Great Lakes (particularly the prairie peninsula). It has been reliably reported from 13 states and 1 province (Sheviak and Bowles 1986, Bowles 1991). It is now known from 50 populations in 7 states (Illinois, Iowa, Maine, Michigan, Ohio, Virginia and Wisconsin) (Bowles 1991, Engel 1992) and 20 extant populations in southern Ontario. The northeastern distribution limit is apparently Aroostook County, Maine based on the most comprehensive map available (Sheviak and Bowles 1986).

An earlier map produced by Bowles (1983) shows an occurrence in New Brunswick, which is an error (see Hinds 1986). It is not included in the most recent work on the flora of Nova Scotia, Roland’s Flora of Nova Scotia, Vol. 2 (Zinck 1998). Reports from Nova Scotia (e.g. Case 1987) therefore are excluded.

Canadian Range

Brownell (1984) indicated that Platanthera leucophaea occurs in Manitoba and Ontario; however, as discussed in section 4.0 on taxonomy, in Canada the Eastern Prairie Fringed-orchid occurs only in southern Ontario. Figure 2 indicates the distribution of the 34 known current and historical reliable occurrences. Lambton County, and southwestern Essex County contain many concentrated occurrences and, therefore, Figure 2 shows only 25 dots. Distinct occurrences are considered to be separated by at least 1 km.

Figure 2. Map of southernOntarioshowing locations of Platanthera leucophaea. Dots show populations believed to be currently existing and half-dots show populations that are not extant. A population was considered no longer extant if: 1) not seen or reported for over 20 years; or 2) known to be destroyed by urbanization, conversion to agriculture, loss due to succession etc.; or 3) not seen in the 1990s despite at least 4 searches during the flowering period.

Figure 2. Map of southernOntarioshowing locations of Platanthera leucophaea. Dots show populations believed to be currently existing and half-dots show populations that are not extant.

Almost all occurrences are based on specimens or photographs in various herbaria in North America (see Brownell 1984). Unsupported locations have been accepted based on personal observations of the authors and/or another reliable field botanist. Detailed location information including site name, UTM, latitude and longitude, are in a confidential file, maintained by the Ontario Ministry of Natural Resources, which is available on a "need to know" basis for conservation purposes.

An additional site near Brockville was previously known but not reported in Brownell (1984) due to confusion in labelling data. The new sites are outlined in Table 1. Intensive field studies from 1984-86 in Lambton County and additional interest due to COSEWIC designation of the species probably contributed to the finds. There has been a generally increasing interest in natural history and field botany over the past decade as evidenced, for example, by the organization of the Field Botanists of Ontario in 1987, but focussed field studies have been most productive in finding new locations.

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