Small-flowered tonella (Tonella tonella) COSEWIC assessment and status report: chapter 2

Executive Summary

Small-flowered Tonella
Tonella tenella

Species Information

Tonella tenella (small-flowered tonella; Figwort family) is a slender, ascending to sprawling, annual herb from a delicate taproot. The smooth, often branched stems are 5-25 cm tall with opposite leaves. The leaves are smooth (or soft-hairy on the upper surface). The lowermost leaves are stalked, ovate to round, 1-2 cm long and few-toothed. The middle and upper leaves become un-stalked upward and are deeply 3-lobed with the segments progressively narrowing upward. The uppermost leaves are reduced and often entire. The inflorescence consists of one to several long-stalked flowers in the axils of the bracts with smooth or minutely glandular-hairy stalks. The corollas are blue and white, short-tubular, 2-4 mm wide, and 2-lipped with the upper lip 2-lobed, the lower lip 3-lobed, and the middle lobe the largest. The calyces are up to 3 mm long, and deeply 5-lobed with the lobes longer than the tube. The 4 stamens are exserted and the fruits are ovate to globe-shaped capsules. The 2 to 4 seeds are large, 1-1.5 mm long and wingless.

Distribution

The southwestern British Columbia occurrence of Tonella tenella is disjunct from its main range in southern Washington (Columbia River gorge), through Oregon to central California. In Canada, T. tenella is known only from the west side of Saltspring Island in the Gulf Islands of southwestern British Columbia.

Habitat

Tonella tenella occurs on west-facing slopes on stable talus. This talus occurs in open Acer macrophyllum(big-leaf maple)-Arbutus menziesii(Arbutus)forests, where associates include Galium aparine(cleavers), Cardamine oligosperma (little western bitter-cress), Claytonia perfoliata(miner’s-lettuce), Bromus sterilis (barren brome), and Collinsia grandiflora (large-flowered blue-eyed Mary) or in open Douglas-fir -Arbutus –Quercus garryana (Garry oak) forests with Kindbergia oregana (Oregon beaked moss), Dicranum sp. (heron’s-bill mosses), Melica harfordii (Harford’s melic), Torilis japonica(upright hedge-parsley) and Bromus sterilis(barren brome).

Biology

Species of Tonella, along with its sister genus, Collinsia (blue-eyed Mary) of the tribe Collinsieae, are self-compatible annuals. Tonella tenellais considered a small-flowered type and doesn’t maintain spatial separation of anthers and stigmas early in flowering and therefore, doesn’t experience the subsequent delay in self-pollination. Instead, anther-stigma contact and self-pollination occur early. Furthermore, the stigmas are receptive to pollen-tube growth early in Tonella species. Low elevation pollinators for the tribe include a variety of bees including Bombus (bumblebees).

Population sizes and trends

Four small subpopulations of Tonella tenella were recently confirmed in 2002 at the Saltspring Island site. These subpopulations, plus an earlier (1976) subpopulation record from the same site but not relocated in 2002, occur in a narrow band extending up the mountainside for approximately 425 m. The subpopulations consisted of 30 to 150 plants with areas of 1 to approximately 40 , respectively. Since the plant is inconspicuous and extremely difficult to detect, it is quite likely other subpopulations occur on the slope.

Limiting factors and threats

The most immediate threat to Tonella tenella in British Columbia is habitat destruction through a housing development at the single location on private waterfront property. Suppression of both natural and human-induced fires could also affect T. tenella survival. In the absence of fires, high fuel loads build and catastrophic fires could result. The vegetation at the site is dominated to a large extent by introduced species, particularly grasses, including Bromus.

Special significance of the species

Tonella tenella occursin one location within a unique habitat in Canada, the Garry oak ecosystem, which is restricted to southeastern Vancouver Island, several islands in the Gulf of Georgia and a narrow strip of adjacent mainland in British Columbia. This vegetation type has been greatly reduced by urban development in the last one hundred years, and contains a high number of rare species. Furthermore, the populations are unique as they are at the northern extent of their geographic range. Peripheral populations are often genetically and morphologically divergent from central populations and therefore provide plasticity for the species as a whole.

Existing protection or other status designations

The British Columbia Ministry of Sustainable Resource Management Conservation Data Centre ranks T. tenella as an S1 or “red-listed” species in British Columbia. This is the most critical rank that can be applied to species at the provincial level and indicates that the species is "critically imperiled because of extreme rarity.” The T. tenella site occurs on private land with no active stewardship in place by land owners. Furthermore, no provincial endangered species legislation exists. Federal legislation applies mainly to federal lands but may be invoked if provincial actions fail to adequately address the conservation of a species on private lands.

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. Species designated at meetings of the full committee are added to the list. On June 5th 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 for 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 or genetically distinct 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)Footnote1
A species of special concern because of characteristics that make it particularly sensitive to human activities or natural events.

Not at Risk (NAR)Footnote2
A species that has been evaluated and found to be not at risk.

Data Deficient (DD)Footnote3
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.

 

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