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Wisconsin Plant of the Week

Lysimachia thyrsiflora L.

Primulaceae (Primrose Family)

Common Name:

tufted loosestrife


Tufted loosestrife, one of several “yellow loosestrifes”, is a native perennial that grows in swamps, at the edge of bogs and in wet prairies, where it’s usually partly shaded by taller vegetation. Although it’s not a true bog species, it has a low tolerance for calcium and so is usually found on peaty soil. It spreads by seed and by long rhizomes.

Plants are erect, unbranched, and less than 0.7 m tall.  The leaves are opposite, up to 12 cm long, undivided, with a pointed tip and tapered at the base. Pits or dots are visible on the leaves with a hand lens.  The flower clusters form in the axils of the leaves, but only the leaves in the middle of the stem.

Dense spike-like flower clusters bloom in June on stalks, up to 4 cm long. Each tiny flower has six yellow petals with black or purple spots, also only visible with a lens.

Like all the species in the Primrose Family, Lysimachia petals are joined together and each stamen is fused to the middle of a petal. The Primulaceae are the “true primroses”, not to be confused with the Onagraceae or the “evening-primroses”.  Purple loosestrife (Lythrum salicaria) is in yet another family, Lythraceae, and not at all related to the yellow loosestrifes.

  • Origin of the name: Lysimachia, lysis, Gr., to loosen or release; mache, Gr., a struggle; refers to the practice of putting the flowers under the yoke of oxen to repel insects; thyrsiflora, thyrsos, Gr., thyrse, refers to the pyramid-like arrangement of the individual flowers.
  • Range:  Circumboreal, in N. Amer. south to NJ, MO, CA
  • WI Range:  Statewide; more common north and east
  • Common associates:  Bluejoint grass, horsetails, marsh fern, poison sumac
  • Wetland Indicator Status: OBL
  • Coefficient of Conservatism: C = 6 (MI);  C = 9 (S&W)
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