Flower:

Rounded clusters about ½ inch across of 5 to 10 star-shaped, nearly stalkless flowers at the end of a naked stalk, ½ to 2 inches long, arising from the leaf axils, which are typically just under the water surface. Flowers are 1/16 to 1/8 inch across with 5 small white to green petals and 5 spreading white stamens.

Leaves and stems:

Leaves are round to kidney-shaped, ¾ to 3 inches wide, with 3 to 7 rounded toothed, shallow lobes around the edge and a deep cut at the base, on a smooth stalk 2 to 12 inches long rising far above the flowers.

The leaf stalk is attached on the underside of the leaf at the base of a deep sinus, appearing to be in the center of the blade. The blade is held horizontal, parallel to the ground. Stems are on or just below the water's surface, horizontal, heavily branched, rooting at the nodes and often creating dense colonies with a thick tangle of roots.

Notes:

Floating Pennywort in Minnesota is a disjunct population of what is primarily a southern species. The Shakopee Mdewakanaton Sioux Community first documented the species on their lands in Scott County in 2007, where there is a stable population in three wetlands. It was possibly transported here by waterfowl. It is rumored to have been discovered in Dakota County as well but, as far as we know, has not been confirmed. Sold around the world as a water garden plant, it has become invasive in Australia and parts of Europe due to its propensity to form dense colonies. Also discovered in Wisconsin in 2010 at Delavan Lake, the WI DNR declared it a non-native invasive species, too, and is apparently working on eradication. A similar species is American Water Pennywort (Hydrocotyle americana), a Minnesota Special Concern species, which is decidedly branched with stalkless flower clusters in the leaf axils, and not typically found in open water. The leaves of Floating Pennywort somewhat resemble those of a few buttercup (Ranunculus) species but the aquatic forms all have very finely divided submersed leaves which Hydrocotyle lacks, as well as distinctly yellow flowers.