Flower:

Flowers are single at the tip of a leafless stem, about ¼ inch across with 2 to 5 yellow petals that quickly fade to whitish and wither. In the center is a bulb of tiny green pistils surrounded by a ring of yellow stamens.

Around the base are 5 erect to spreading, narrowly egg-shaped sepals that are as long as or slightly shorter than the petals. Stems and sepals are densely covered in white, woolly hairs.

Leaves and stems:

Leaves are basal, up to 1½ inches long and to ½ inch wide, spatula-shaped in outline with 3 to 5 blunt-tipped, linear lobes that may be further divided into 2 or 3 smaller lobes. Flowering stems are erect to ascending, single or more often multiple from the base, and green. Leaves and stems are covered in white, woolly hairs.

Fruit:

The center bulb elongates to an oval to cylindric seed head up to about 2/3 inch long, maturing from green to light brown. Seeds are about 2 mm long, densely covered in woolly hairs and have a broad, sharply pointed, persistent beak about 1/8 inch long, making the seed head rather prickly.

Notes:

Bur Buttercup, also known as Ceratocephala testiculata, is a tiny thing, usually less than 4 inches tall, and easily overlooked. It is much more common in western North America where it is something of an agricultural pest and toxic to livestock, but is spreading eastward. Interestingly, in Minnesota all recorded locations so far have been in campgrounds, which means seed are likely spreading on car and camper tires. Expect to see more of this in the coming years. It is not likely to be confused with any other species. The short stature, woolly hairs, finger-like divided basal leaves, yellow flowers with 2 to 5 petals, and the prickly seed heads make it easy to ID. One reference noted that the flowers are only open for a few hours in the early afternoon, but we can't confirm that.