Helianthemum canadense (Canada Frostweed)
|Also known as:||Common Frostweed|
|Habitat:||part shade, sun; dry sandy soil; prairies, dunes, savanna, barrens|
|Bloom season:||May - June|
|Plant height:||8 to 24 inches|
|Wetland Indicator Status:||none|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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A single stalked flower at the tip of the stem or branch, sometimes 2 but only one flower open at a time. Flowers are ¾ to 1¼ inch across, with 5 yellow petals and 10 or more orange-tipped stamens fanning around a small central column, the stamens often clustered on one side of it. Later in the season, tight clusters of petal-less, self-pollinating (cleistogamous) flowers develop in the axils and tips of branches.
Behind a flower are 5 green to red-tinged sepals, the inner 3 broadly triangular, the outer 2 very narrow and half as long to nearly as long as the inner. Sepals are covered in a mix of short star-shaped hairs and long, spreading to ascending hairs.
Leaves and stems:
Leaves are alternate, up to 1¼ inch long and to 1/3 inch wide, narrowly elliptic or wider above the middle, pointed or blunt at the tip, tapering at the base, and stalkless. The upper surface is shiny but covered in short star-shaped hairs mixed with scattered, long, unbranched hairs. Leaves on branches are typically smaller than those on the main stem, and do not typically have the long, unbranched hairs.
Leaf undersides are densely covered in only the short, star-shaped hairs, giving a gray-green appearance. Stems are round and hairy, green or brown, and initially unbranched, developing several ascending branches after the initial yellow-petaled flower has finished blooming. The branches rise well above the top of the stem.
Fruit is a round capsule enclosed by the persistent sepals, very much resembling the cleistogamous flowers. Fruit developed from yellow-petaled flowers are larger and contain more seeds than fruit developed from cleistogamous flowers.
Minnesota is on the western fringe of this species' range, and Canada Frostweed was tracked in the state for a number of years. In the DNR's big Rare Species overhaul of 2013 it was designated Special Concern, citing its fragile, remnant sandy habitats are all at risk from grazing as well as encroachment of woody and non-native invasive species. It is very similar to the more common Hoary Frostweed (H. bicknellii) but with 2 distinct differences: H. bicknellii lacks the long, unbranched hairs on leaves and sepals, and its later branches do not rise much above the tip of the stem. H. canadense starts and ends blooming 2 or 3 weeks earlier than H. bicknellii, but there is overlap. Many references also note on H. bicknellii the base of leaves is wedge shaped (not tapering) and the narrow, outer sepals are all about as long as the inner, but these traits are not always distinct or consistent. Our observations were the length of outer sepals in particular can be variable on both species. We also observed that H. bicknellii tends to be more leafy than H. canadense, particularly on the later branches. In some references, H. canadense goes by the synonym Crocanthemum canadense.
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Where to buy native seed and plants ↓
- Canada Frostweed plants
- branches rising above the main stem
- a pollinator
- comparison to Hoary Frostweed
- sepal comparison to Hoary Frostweed
Photos courtesy Peter M. Dziuk taken at Sand Dunes SNA, Houston County, Sherburne National Wildlife Refuge, Sherburne County, and Whitewater Wildlife Management Area, Winona County.
Have you seen this plant in Minnesota, or have any other comments about it?