Small-flowered sand-verbena COSEWIC assessment and status report: chapter 2

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Executive Summary

Species information

Small-flowered sand-verbena Tripterocalyx micranthus (Torr.) Hook. is an annual species and a member of the four o'clock family (Nyctaginaceae). It is a much-branched plant, 2-5 dm high with trailing branches, up to 6 dm long, with ascending tips. The succulent, pale stems are enlarged at the nodes. The paired leaves are entire, somewhat round, and have prominent veins. Leaf blades are 2-6 cm long, 1-3 cm wide. The tiny greenish-white flowers are quite showy as they are arranged in dense clusters with a ring of bracts underneath. Flowers lack petals but have 5 petal-like lobes formed into a long tube, 5 mm in width. When the ovary ripens into the fruit, the base of the calyx tube becomes transformed into a winged structure, closely enclosing the fruit and aiding in its dispersal. These winged fruits are pale green with a pink blush. The fruit is about 2 cm long with 2-3 thin, papery, strongly veined nerves.

Distribution

Small-flowered sand-verbena is confined in the wild to western North America. In Canada the species is restricted to southeastern Alberta (6 sites) and southwestern Saskatchewan (1 site) near the Alberta border along the South Saskatchewan River.

Habitat

Small-flowered sand-verbena is found in dry habitats, particularly in loose sands of dune and sand hill areas. Some element of active sand is usually required. Common species associated with small-flowered sand-verbena are spear grass (Stipa comata), sand grass (Calamovilfa longifolia), buckbrush (Symphoricarpos occidentalis), rose (Rosa acicularis), chokecherry (Prunus virginiana), silverberry (Elaeagnus commutata), Indian rice grass (Oryzopsis hymenoides), scurf pea (Psoralea lanceolata), June grass (Koeleria macrantha), sand dropseed grass (Sporobolus cryptandrus), golden aster (Heterotheca villosa) and petiolate sunflower (Helianthus petiolaris).

Biology

Small-flowered sand-verbena is an ephemeral species. Flowering occurs mostly in middle June with fruit set in middle July at Canadian sites. Seeds are disseminated by wind or water. Since the species is an annual, establishment of seedlings can be expected downwind or downstream from the original population. This assumption can be useful in relocating old populations.

Small-flowered sand-verbena is superbly adapted for survival within its sand dune habitat. Adaptation of annuals in arid conditions requires prompt response to irregularly occurring favorable growth periods, rapid completion of the reproductive process, and production of massive numbers of durable seeds that can survive long periods of unfavorable environment. The formation of a viable seed bank is vital for the future survival of the species within its sandy habitat.

Population sizes and trends

Only one plant was found at the Bow Island site in Alberta during the 2001 survey of all known Canadian sites. In 1994, 1 plant was found at the Suffield National Wildlife Area site. Population numbers have crashed from the 1000 plant total population reported in the previous status report for the species (1992). Habitat loss due to dune stabilization and severe drought conditions are the most likely primary factors contributing to the population crash.

Limiting factors and threats

There has been a major loss of habitat over the Canadian range of small-flowered sand-verbena as a result of dune stabilization. Small-flowered sand-verbena requires some element of active sand for its survival. No suitable habitat remains at two of the five known Alberta sites. Little suitable habitat remains at any of the other Alberta sites or the single Saskatchewan site. The likely factors contributing to dune stabilization are the discontinuation of historical fire and browsing patterns. Also, the potential spread of the species has been limited by historical and recent changes in land use. The cultivation of lands surrounding the sites limits potential habitat. The primary Canadian site is located in a major oil and gas field. Finally, the spread of weedy species into dune areas may contribute to the process of dune stabilization.

Special significance of the species

Small-flowered sand-verbena has no known commercial uses. It has limited horticultural uses as a result of its preference for drifting sand.

COSEWIC Mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) determines the national status of wild species, subspecies, varieties, and nationally significant populations that are considered to be at risk in Canada. Designations are made on all native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fish, lepidopterans, molluscs, vascular plants, lichens, and mosses.

COSEWIC Membership

COSEWIC comprises representatives from each provincial and territorial government wildlife agency, four federal agencies (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biosystematic Partnership), three nonjurisdictional members and the co-chairs of the species specialist groups. The committee meets to consider status reports on candidate species.

Definitions

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.

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.