Ranunculus flammula L.
Family: Ranunculaceae
creeping spearwort, spearwort buttercup
Ranunculus flammula image
from USDA Plants website  
Etymology: Ranunculus: from Latin rana, "little frog," because many species tend to grow in moist places
Plants: creeping, perennial, 4"-20" long, semi-aquatic forb with some form of the plant submersed; stems the same width as the leaves
Leaves: in small clusters from the stem nodes, linear, not tapered, blunt tipped; not deeply lobed
Flowers: yellow, 5-parted, 1/4"-1/2" wide, the petals about twice as long as the sepals, oblong, and with a wider tip; solitary flower on 1"-6" stalk from some of the stem nodes; blooms July-Sept.
Fruits: dry seed with a short, erect beak fruit drawing
Habitat: wet to moist; shallows, shores, water to 7' deep; in sandy, gravelly soil
Hazardous: Careful, this plant is hazardous!
Conservation Status: Native