Bidens discoidea (Discoid Beggarticks)
|Also known as:||Swamp Beggarticks|
|Habitat:||part shade, sun; swamps, mucky lake margins|
|Bloom season:||July - September|
|Plant height:||12 to 30 inches|
|Wetland Indicator Status:||GP: FACW MW: FACW NCNE: FACW|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Flower heads are numerous on branching stalks at the tips of stems and arising from leaf axils in the upper plant. Heads are small, petal-less (no ray flowers), the yellow central disk 1/8 to about 1/3 inch across. The 5 to 7 inner bracts are light green with numerous vertical lines, oblong to lance elliptic, smooth, overlapping, erect with the pointed tips flaring outward slightly, and just about as long as the flower head is tall. The 3 to 5 leafy outer bracts are spreading, linear to spatula shaped, several times longer than the flower head is wide, with or without sparse cilia-like hairs around the edges.
Leaves and stems:
Stem leaves are opposite, on slender stalks, and mostly compound in 3s but may be simple near the flower heads. Leaflets are oval to narrowly lance-shaped, coarsely toothed, gradually tapering to a sharply pointed tip, and mostly hairless except for sparse hairs around the edges or along the veins on the underside. The middle leaflet is the largest, up to 4 inches long and 1½ inches wide, and longer stalked than the lateral leaflets. Stems are smooth and slender, much branched, often purple.
With a broad range throughout the eastern US and a preference for watery habitats, one might assume Bidens discoidea would be common in Minnesota. But surprisingly its occurrence is restricted to a relatively few lakes in our northeast central counties where it is found along boggy shorelines and floating mats. While its obscure profile and non-recreational habitat may impact its under-reporting, the Minnesota DNR had categorized it as a tracked species and elevated it to Special Concern in 2013. Most similar are Devil's Beggarticks (Bidens frondosa), which has leaves compound in 3s or 5s and up to 12 outer bracts that are conspicuously hairy around the edges, and Purple-stem Beggarticks (Bidens connata), which does not have compound leaves but also has more than 5 outer bracts.
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Photos courtesy Peter M. Dziuk taken at Lake Eleven in Kanabec County.
Have you seen this plant in Minnesota, or have any other comments about it?