Branched bartonia (ssp. paniculata) COSEWIC assessment and status report: chapter 7

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Population Sizes and Trends

In early September of the 1991 field season, the writer investigated and confirmed two branched bartonia sites. Other field botanists had confirmed additional sites around that time and their field data is incorpo­rated below. The region in which branched bartonia is found is well known for its Atlantic Coastal Plain Disjuncts. It has been extensively surveyed over a period of many years by knowledgeable botanists and naturalists. At the time of the original status report, there were five populations known in the province, all of which had been verified since 1973. Four of the populations occur in Muskoka District and one occurs just outside Muskoka in Parry Sound District. A sixth population (Site 4) was found in 1990 (Oldham, 2002) but was not listed in the original status report (White, 1991).

Since the time of the original status report, one new location has been found (Site 5) to bring the total known to seven. For the present update, the writer conducted three days of fieldwork (Sept. 11-13, 2002). A population at site 2, confirmed in 1991, could not be relocated in 2002 despite a careful search in a well-defined location and it may have disappeared. Since branched bartonia is a small annual plant that is difficult to locate, it is not possible to say at most sites if the species is increasing or declining.

A total of 213 plants were located in 2002. Some considerable variation in total numbers is apparent at some sites over the course of several years (cf. Sites 4 and 5) but it is uncertain whether these represent gradual changes or more abrupt fluctuations. It is likely that the total numbers of plants are much higher than presently recorded. 

The following is an overview of the seven documented sites (locations are mapped in Figure 3):

• Site 1supported a small colony of branched bartonia in a rather unusual habitat at the edge of a sand spit. It was discovered in 1983 by Irene Wisheu. Approximately 10 to 20 plants were found (I. Wisheu, pers. com., 1991). It has not been searched for since its discovery in 1983 and its current status is unknown. Given the isolated nature of the site, branched bartonia is presumed to be still extant there.
• Site 2supported a small population that was first located by Jim Goltz in 1975 with the discovery of one plant. The species was not seen there again despite searches for it (R.E. Whiting, pers. com., 1991) until the author's fieldwork in 1991. Two separate subpopulations were located, one with two plants and the other with 14 plants. This site is rather vulnerable due to the presence of the Canadian National Railway that passes along the lakeshore within several metres of the plants. The colony could be eliminated if the railway embankment was widened with additional fill along the shore. Despite careful searching of the site by the author in 2002, no branched bartonia could be found and the species may have disappeared there.
• Site 3 is the site of the plant's first discovery in the province in 1973 by R.E. Whiting and represents one of the larger known populations. Branched bartonia occurs in this bog as a number of apparently discrete colonies. The author found three such colonies in 1991 of from 22 to 32 plants within an area of about 50 m by 500 m. Additional site(s) were found in the same bog after the original discovery independently by J. Soper and B. Bowles (R.E. Whiting, pers. com., 1991). In 2002, the author found 4 subpopulations of from one to 16 plants totalling 20 plants.
• Site 4 is an extensive open bog that supports a small population of branched bartonia (12 widely scattered plants). This colony was discovered in 1990 by Jim Goltz but was not listed in the original Status Report (White, 1991). In 2002, the author found 6 subpopulations of from one to 45 plants totalling 122 plants.
• Site 5 is an extensive open fen that supports a large population of branched bartonia (over 200 plants seen in three subpopulations). This colony was discovered in 1997 by Jim Goltz, Richard Aaron, and Shirley Lee. In 2002, the author found six subpopulations of from one to 25 plants totalling 52 plants.
• Site 6 is a small bog that contains a small colony of branched bartonia. It was discovered in 1977 by Jim Goltz but only a few plants were located at that time (R.E. Whiting, pers. com., 1991). About 30 plants were found in 1979 (Oldham, 2002). In 2002, the author found three subpopulations of from one to 16 plants totalling 19 plants.
• Site 7 is an extensive bog that supports at least a small colony of branched bartonia. This site is now protected by its inclusion within the O'Donnell Point Nature Reserve. This colony was discovered in 1977 by Stephen Darbyshire, Bill Crins, Vivian (Brownell) Catling, and Loney Dickson. Approximately 20 to 30 plants were seen at the site although extensive searches were not carried out (B. Crins, V. (Brownell) Catling, and S. Darbyshire; pers. com., 1991). It has not been searched for since its discovery in 1977 and its current status is unknown. Given the isolated nature of the site, branched bartonia is presumed to be still extant at the site.

A summary of populations and sizes is provided in Table 1.