Bacopa rotundifolia (Water-hyssop)
|Also known as:||Disk Water-hyssop, Round-leaf Water-hyssop|
|Habitat:||sun; mud or shallow water; pools, ponds, lakes, ditches|
|Bloom season:||May - June|
|Plant height:||sprawling to 2 feet|
|Wetland Indicator Status:||GP: OBL MW: OBL NCNE: OBL|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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1 or 2 stalked flowers arising from leaf axils along most of the stem. Flowers are about 1/3 inch long, tubular with 5 white, rounded, spreading lobes. The lobes are slightly shorter than the tube and are yellow at the base and into the throat of the tube. Inside the tube are 4 white-tipped stamens that turn black and a 2-parted style. Flower stalks are hairy and not longer than the associated leaf.
Leaves and stems:
Leaves are opposite, ¼ to 1¼ inch long and to 1 inch wide, round to elliptical, toothless, stalkless, clasping the stem, and with 6 or more veins radiating from the base. New growth is typically hairy. Stems are stout and succulent, smooth to finely hairy, green to reddish, floating when in shallow water and sprawling when stranded in mud, rooting at the nodes and creating dense mats.
Fruit is a round to oval capsule containing numerous small, tan seeds.
Water-hyssop is widely distributed in the central US, typically found in the shallows of pond and lake edges, wet ditches, and muddy shores. In Minnesota, its habitat is more restricted to the short-lived, rainwater pools of rock outcrops and prairie ponds. These pools typically dry up in early summer and Water-hyssop disappears soon thereafter. According to the DNR, there were only 22 known occurrences in the state, mostly small populations, and most of these at risk from grazing, herbicide use, and from bedrock mining in particular. It was listed as a Special Concern species in 1984 and elevated to Threatened in 2013. In 2014, however, significant new populations were discovered in the quiet waters and mud flats of the Mississippi River along the Dakota-Washington county border. Its status as a Threatened species may or may not change with these new finds.
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- early growth, floating in a vernal pool
- first blooms
- a mat of Water-hyssop
- a mat of Water-hyssop in a drying pool
- Water-hyssop rock outcrop habitat
- Water-hyssop in quiet waters of the Mississippi River
Photos courtesy Peter M. Dziuk taken at Blue Mound State Park, Rock County, and in Big Stone County. Photos courtesy Terry Serres taken in Dakota County.
Have you seen this plant in Minnesota, or have any other comments about it?