Flower:

Single 1/3 to ½ inch flower on a slender stalk arising from leaf axils along branching stems. Flowers are tubular with 5 lobes, the 3 lower lobes round to oval and about equal in size, the upper lip shallowly lobed in 2 parts. Color is white to light blue or violet in color, typically with deeper colored markings on petal edges, throat and tube. Inside the tube are 2 fertile stamens, 2 club-shaped sterile stamens, and a single style. Sepals are fused with sharp, narrow teeth that extend less than half way up floral tube.

Leaves and stems:

Leaves are opposite, up to about 1 inch long and ½ inch wide, becoming slightly smaller as they ascend the stem, hairless, glossy, egg shaped to elliptical, broadest towards base, tapered to a blunt tip, stalkless to nearly clasping at the base. Edges are toothless or with a few to several widely-spaced, shallow teeth. Stems are multiple from the base, branched, shiny, smooth, square, and erect to ascending to prostrate, often rooting at the lower nodes.

Fruit:

Fruit is an oval-elliptic to nearly round capsule up to ¼ inch long, containing numerous yellowish seeds.

Notes:

False Pimpernel, like most annuals, tends to emerge in different places year after year. My first images of it came from a plant that apparently popped up from the seed bank in a thin patch of lawn in Lino Lakes. A similar species is Hedge Hyssop (Gratiola neglecta), which has yellowish to white flowers, and a round stem covered in short hairs, where False Pimpernel has smooth, square stems and usually violet colored flowers.

Many references list two varieties, both widespread within the same range and both recorded across Minnesota, but Flora of North America considers it a single variable species and we won't dispute it. For the splitters, var. dubia is said to have larger leaves (to 3 cm long) with lower ones more narrow at the base and flower stalks that barely surpass the attending leaf; var. anagallidea (a.k.a. L. anagallidea), has smaller leaves (to 1.5 cm long), mostly broad at base and with flower stalks much longer than attending leaves.