Flower:

Single flowers at the tip of a naked stalk arising from the leaf axils. Flowers are about 1 inch diameter with 7 to 12 shiny yellow petals, each 10 to 15 mm long. In the center is a tiny greenish bulb of pistils surrounded by numerous yellow stamens.

The calyx surrounding the base of the flower has 3 or 4 light green, egg-shaped sepals that are more or less half as long as the petals. Sepals and flower stalks are all hairless.

Leaves and stems:

Leaves are mostly basal with a few alternate and/or opposite, up to about 1½ inches long and wide (1.8-3.7 x 2-4 cm), heart to kidney-shaped to nearly round, heart-shaped at the base, rounded or blunt at the tip, the edges toothless or scalloped, and surfaces hairless. Stems are branched, erect or prostrate from the base and rising toward the tip (decumbent), light green and hairless.

Plants can form dense mats from underground tubers that send out new shoots.

Fruit:

The center bulb develops into a round seed head 6 to 8 mm in diameter. One plant can produce about 70 seeds, which may or may not be viable. After flowering, tiny round, white bulbils develop in leaf axils, which drop off and form new plants.

Notes:

Lesser Celandine, formerly Ranunculus ficaria, is low-growing, mat-forming, and can start blooming even before all the snow has melted, as early as late March. Its primary methods of reproduction are from the tuberous roots and bulbils, which cause it to form dense monocultures that effectively crowd out native spring ephemerals. It bears a vague resemblance to Marsh Marigold (Caltha palustris), which is a much, much larger plant with much larger leaves and flowers. The leaves also bear a resemblance to another invasive species, Garlic Mustard (Alliaria petiolata), with which it may grow. Some references mention several vars, but these are not universally accepted.

Lesser Celandine is not currently widespread in Minnesota but was designated a Restricted Noxious Weed in Minnesota in 2023, presumably due to its propensity to form dense mats and preferred floodplain habitat where flood waters can easily transport its tubers and bulbils to new locations. The Minnesota Dept. of Agriculture reports it covering a 400-acre area in Ohio. Yikes.