Rare Species Guide

  Synonyms

Helianthemum canadense

  Basis for Listing

Crocanthemum canadense (Canada frostweed) occurs in dry and sandy prairie openings, savannas, and barrens in eastern Minnesota (Eastern Broadleaf Forest and Laurentian Mixed Forest provinces). There are approximately 30 records of this species in the state, which by itself qualifies it as relatively rare. Unfortunately, many of these records are from sites that are known to have already been destroyed or degraded, and the trend is worsening. The habitats are generally small and fragile, and a disproportionate number of them are in the path of various development projects. For these reasons, Crocanthemum canadense was given the status of special concern in 2013. It may soon warrant a status upgrade, if the development trend continues.

  Description

The stems of C. canadense are clustered, erect, and 15-30 cm (6-12in.) tall. Stems are essentially unbranched at the start of the flowering period, developing branches later. Most flowers are cleistogamous and have no petals. They are small self-fertilizing flowers that never open. However, each stem will have 1 chasmogamous flower that has 5 conspicuous yellow petals, which are produced early in the season. Unfortunately, each flower lasts only a single day, so do not count on seeing a petaliferous flower. The fruit of the chasmogamous flowers range from 6-7 mm (0.24-0.28 in.) in length and bear 30-45 seeds, whereas the fruit of the cleistogamous flowers are 2-3 mm (0.08-0.12 in.) in length and have fewer seeds (5-10). Leaves of the main stem are 2-3 cm (0.8-1.2 in) long and 5-8 mm (0.2-0.3 in.) wide. They are elliptic in shape, and the lower surface is densely hairy.

There is a closely related species, Crocanthemum bicknellii (hoary frostweed) that occurs in the same habitat type but is much more common. It differs from C. canadense by having 2-10 petaliferous flowers, instead of just 1, and by having the subsequent non-petaliferous flowers failing to overtop the earlier petaliferous flower (Daoud and Wilbur 1965).

  Habitat

Crocanthemum canadense is found primarily in high quality remnant sand savannas, sand prairies, dunes, and barrens. These habitats are characteristically dry, sunny for all or most of the day, and sparsely vegetated. Habitats that have been plowed or cleared in the past do not appear to support viable populations of this species.

  Biology / Life History

Crocanthemum canadense is unusual, but not unique, in that it produces cross-pollinating petaliferous flowers early in the season and self-pollinating non-petaliferous flowers late in the same season. Both types of flowers will produce viable seeds, though the seedlings that result from the self-pollinated flowers will be genetically identical to the parent plant. This is usually thought to be an adaptation to harsh environments, where cross-pollination cannot be assured.

Several types of bees, including bumblebees, have been observed pollinating the large yellow chasmogamous flowers. Seed capsules produced by both chasmogamous and cleistogamous flowers mature in 3-4 weeks. Seeds lack a specialized dispersal mechanism, falling close to the parent plant. It has been reported that seeds developing from chasmogamous flowers germinate readily; whereas seeds from cleistogamous flowers germinate poorly and may remain dormant in the seed bank until exposed to fire (fide Newell 2007). Apparently, vegetative reproduction does not occur in C. canadense.

Although experimental evidence is not available to reveal the environmental tolerances of C. canadense, it can be surmised from its choice of habitat that C. canadense is drought tolerant, shade intolerant, and fire/disturbance dependent. Disturbance, other than fire, might include wind or water erosion of the soil and the activities of burrowing animals. Such disturbances, however, may be slight, localized, and episodic compared with the likely destructive effects of row-crop agriculture, road building, or gravel quarrying.

  Conservation / Management

A population of C. canadense that is established in an intact and full-functioning savanna or prairie community will need very little, if any, active management. In some cases, dormant season controlled burns may be helpful in managing excessive shrub growth. In all cases, the habitat must be protected from vehicle trespass. The loose and sandy soil is very fragile, and just about any vehicle traffic will cause damage. Livestock grazing is also injurious, especially on slopes and should be excluded from all sites where C. canadense occurs. One inevitable consequence of grazing is the invasion of non-native species, which can severely degrade the habitat. Spotted knapweed (Centaurea stoebe) is perhaps the most serious invader of dry  and sandy soil in Minnesota, and it must be prevented from getting established.

  Best Time to Search

The best time to search for Crocanthemum canadense is when flowers or fruits are present, which is usually between about June 1 and October 15. Prime months would probably be July and August.

  Authors/Revisions

Welby Smith (MNDNR), 2018

(Note: all content ©MNDNR)

  References and Additional Information

Daoud, H. S., and R. L. Wilbur. 1965. A revision of the North American species of Helianthemum (Cistaceae). Rhodora 67:63-82, 201-216, 255-312.

Marinelli, J., and J. M. Randall, editors. 1996. Invasive plants: weeds of the global garden. Brooklyn Botanic Garden, Brooklyn, New York. 111 pp.

Minnesota Department of Natural Resources. 2005. Field guide to the native plant communities of Minnesota: the eastern broadleaf forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 394 pp.

Minnesota Department of Natural Resources. 2006. Tomorrow's habitat for the wild and rare: An action plan for Minnesota wildlife, comprehensive wildlife conservation strategy. Division of Ecological Services, Minnesota Department of Natural Resources. 297 pp. + appendices.

Minnesota Department of Natural Resources. 2009. Map of Minnesota's remaining native prairie 100 years after the public land survey. . Accessed 19 June 2009

Newell, R. E. 2007. Nova Scotia provincial status report on rockrose (Canada frostweed) [Helianthemum canadense (L.)Michx.]. Nova Scotia Department of Natural Resources, Halifax, Canada.