Flower:

Several flat clusters (umbels) at the tips of branching stems and arising from upper leaf axils. Umbels are 1 to 2 inches across, made up of 10 to 20 smaller clusters (umbellets), each with 20+ 1/8-inch white flowers. Individual flowers have 5 petals, notched at the tip, 5 stamens and a greenish white center. Flowers around the perimeter of an umbellet typically have enlarged petals on the outer edge.

Around the base of an umbellet are 3 or 4 conspicuous, linear bracts that are hairless, much longer than the flower stalks, and bend down away from the flowers (reflexed). The main umbels lack bracts, though a small leaf resembling a bract may be at the base of the umbel stalk. Flower, umbel and umbellet stalks are ribbed with minute hairs along the ribs.

Leaves and stems:

Leaves are 2 or 3 times compound, up to 5 inches long and wide, triangular in outline. Leaflets are divided and fern-like, medium to dark green, hairless, and somewhat shiny on the upper surface. Basal and lower leaves are largest and long stalked, becoming smaller and stalkless as they ascend the stem.

Stem leaves are sheath-like where the stalk joins the stem, the sheath ribbed and hairless with whitish, membranous edging. Stems are erect, much branched, ribbed, and may have minute hairs along the ribs especially in the upper plant.

Fruit:

Fruits are broadly egg-shaped, slightly flattened, about 1/8 inch (to 4mm) long, and split into 2 seeds.

Seeds are thick-ribbed and narrowly winged. The remains of the style persists at the tip.

Notes:

If you do a web search for Fool's Parsley, you'll get gobs of results praising its medicinal values, notably as a remedy for milk allergies in children as well as a variety of mental conditions. It is, however, quite poisonous. “A Manual of Weeds” by Ada E. Georgia notes “its Greek name means ‘to burn’, which indicates the sort of agony that its victims feel”. Since the leaves look much like the garden variety Italian parsley, the common name seems rather fitting. Fool's Parsley joins the list of non-native carrot introductions that includes Wild Carrot (Daucus carota) a.k.a. Queen Anne's lace, Wild Parsnip (Pastinaca sativa), Poison Hemlock (Conium maculatum), Caraway (Carum carvi), Japanese Hedge-parsley (Torilis japonica), and Wild Chervil (Anthriscus sylvestris). More will come, of that we are pretty certain.

The only collection of Fool's Parsley in Minnesota dates back to 1878 in Lake City, Wabasha County. While this may indicate a hardiness issue, it was more recently discovered at the MN Landscape Arboretum, so it might be persisting after all. The resemblance to Queen Anne's Lace and other white carrot species spreading along roadsides across the state is possibly masking its actual distribution here. Fool's Parsley is most easily distinguished by its hairless leaves, sheaths and stems, the 3 or 4 long, drooping, linear bracts at the base of an umbellet, the main umbels lacking bracts, and the hairless, ribbed fruits. The fern-like leaves are probably most similar to Japanese Hedge-parsley, which has stiff appressed hairs on leaves and stems, 2 to a few thread-like bracts at the base of umbels but not the umbellets, and hooked hairs on its fruit.