Branched bartonia (ssp. paniculata) COSEWIC assessment and status report: chapter 2

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COSEWIC Executive Summary

Species information

Branched bartonia (Bartonia paniculata ssp. paniculata) is an annual herb 1 to 4 dm tall with a green or purple angled and occasionally twining stem. Due to its common habit of growing deeply nestled in sphagnum moss, it generally appears much shorter. The leaves are reduced to minute scales arranged in an essential­ly alter­nate fashion. The inflorescence is usually a panicle of few to numerous, small, white, 4-lobed flowers on divergent or curved ascending branches. The capsule tapers to a blunt tip and averages 4.2 mm long. The seeds average 0.19 mm long x 0.12 mm wide with 1000 to 1500 per capsule. In view of the plant's greatly reduced leaves and thus its limited photosynthetic capacity, branched bartonia may be heterotrophic, i.e., dependent on soil fungi directly or indirectly for much of its organic nutrient requirements. The related subspecies iodandra occurs in Atlantic Canada but is not, overall, of conservation concern in the region.

Distribution 

It has a wide range in the eastern United States from New England south to Louisiana and Texas. In Canada, it occurs only in south­central Ontario.

Habitat

The habi­tat is open graminoid (grass-like vegetation) or low shrub sphagnum bog or fen with scattered Larch and Black Spruce. The substrate is peat. The site temperature may be lower than normal due to the saturated nature of the peat and the proximity of Georgian Bay.

Biology

Branched bartonia is an annual, possibly heterotrophic, species with reproduction only by seed. It is not known how large the seed bank might be or what conditions are necessary for germina­tion.

Population sizes and trends

There are six existing populations. Four stations were reconfirmed in 2002: Site 3 with 20 plants (78 plants in 1991); Site 4 with 122 plants (12 plants in 1990); Site 5 with 52 plants (over 200 plants in 1997); and Site 6 with 19 plants (30 plants in 1979). A fifth population occurs on Crown land (Site 7) at an isolated location along the Georgian Bay shoreline. This population has not been visited since 1977 when it had 20-30 plants; however, it is assumed to be still extant. A sixth population (Site 1) has not been visited since 1983 when it had 10-20 plants, but it is also assumed to be extant. A population at Site 2 was confirmed in 1991 when it had 16 plants, but none could be relocated in 2002 and the population may have disappeared. Most recently, 213 plants have been documented, but an estimate of the total number may exceed 500 plants. Since branched bartonia is a small annual plant that is difficult to locate, it is not possible to say with certainty at most sites if the species is increasing or decreasing in numbers.

Limiting factors and threats

The open sphagnum bog or fen habitat for branched bartonia is wide­spread in southcentral Ontario, and there are potential areas that could have populations of the species. When apparently suitable habitat within the known Ontario range is investigated, however, branched bartonia is rarely found. Members of the Atlantic coastal plain flora, to which branched bartonia apparently belongs, are generally restricted to a rather small area of southcentral Ontario. No imminent threats are known; however, peripheral areas of two sites are being taken over by the invasive shrub black buckthorn (Rhamnus frangula). Continued expansion by this shrub could threaten branched bartonia at these sites. Another population, which could not be re-confirmed in 2002, and may have disappeared, is located adjacent to a railway embankment. If this embankment were to be widened the site could be eliminated.

Special significance of the species

Branched bartonia is a rare plant of sphagnum bogs whose natural significance is largely unknown. The Canadian populations could have some biogeographical significance due to their position some 600 km from the northern edge of the plant's range. Branched bartonia is one of a number of so-called Atlantic coastal plain species having disjunct populations in the Muskoka District of Ontario but with a main range along the Atlantic coastal plain. There is no known Aboriginal Traditional Knowledge of branched bartonia.

COSEWIC History

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk.  On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC Mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species and include the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC Membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal organizations (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biosystematic Partnership, chaired by the Canadian Museum of Nature), three nonjurisdictional members and the co-chairs of the species specialist and the Aboriginal Traditional Knowledge subcommittees. The committee meets to consider status reports on candidate species.

Definitions (After May 2003)

Species: Any indigenous species, subspecies, variety, or geographically defined population of wild fauna and flora.

Extinct (X)

A species that no longer exists.

Extirpated (XT)

A species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)

A species facing imminent extirpation or extinction.

Threatened (T)

A species likely to become endangered if limiting factors are not reversed.

Special Concern (SC) ^Footnotea

A species of special concern because of characteristics that make it particularly sensitive to human activities or natural events.

Not at Risk (NAR) ^Footnoteb

A species that has been evaluated and found to be not at risk.

Data Deficient (DD) ^Footnotec

A species for which there is insufficient scientific information to support status designation.

Canadian Wildlife Service

The Canadian Wildlife Service, Environment Canada, provides full administrative and financial support to the COSEWIC Secretariat.