Sunday, June 25, 2023

Plant profile: Cow parsnip

Caution: The sap of cow parsnip and other members of the carrot family can cause skin rashes and blisters. See below for more information.

Cow parsnip, Heracleum maximum, is a big plant with a big name. This 4- to 8-foot-tall native plant of damp meadows and fields, streamsides, ditches, and low, open woods is named for Heracles or Hercules, the mythic Greek hero of superhuman strength. Even the species name, maximum, hints at its size. Few herbaceous plants are as robust.

A biennial or short-lived perennial in the carrot family, cow parsnip has alternate, divided leaves up to 2 feet across, with smaller, undivided leaves higher on the stem. The leaflets are irregularly lobed, coarsely toothed, and hairy. The petioles of lower and middle leaves are 3 to 10 inches long with sheaths where they meet the stem. Stems are stout, hollow, ridged, and hairy.

Lower leaves of cow parsnip are divided into three lobed, toothed leaflets. This leaf blade (left) is about 18 inches long. Petioles are long with sheaths where they meet the stem (right).

Cow parsnip flowers from late May into early July. Small, white, 5-petaled flowers are in flat-topped, compound umbels, clusters that resemble a collection of little umbrellas. (See Flower Parts for Plant ID to learn more about types of flowers and flower clusters, called inflorescences.) The flowers are pollinated by honeybees and many kinds of native bees and flies, the variety so great that some consider cow parsnip a pollinator magnet.

Cow parsnip flowers are arranged in compound umbels. Each spoke of the umbel extends to another, smaller umbel, called an umbellet. The tiny, white flowers have five petals. 

Fruits are flattened, up to 1/3 inch long and 1/4 inch wide, and brown with dark, vertical lines when they mature in late summer or early fall. They are winged on their edges and so can be dispersed a limited distance by wind. Eventually the fruits split apart and release two seeds. Cow parsnip reproduces only by seed.

These immature fruits of cow parsnip will turn brown when they mature in late summer.

Although the plant is native here and in much of North America, in some states it’s introduced and invasive. In North Carolina, for example, cow parsnip is described as aggressive and insidious and is classified as a noxious weed.

Be Careful

Cow parsnip is rarely considered an ecological problem here, but it should be handled with care. The leaves and stems contain furanocoumarins, compounds that sensitize skin to ultraviolet light. If skin is exposed to plant sap and then sunlight, blistering rashes may result. The condition, called phytophotodermatitis, can take weeks to heal. Always wear gloves, long sleeves and pants when handling this plant, and wash off and cover skin if exposed to the sap. The sap can also damage the eyes, so it’s best to wear eye protection if the plant will be disturbed.

Watch Out for a Look-alike

Giant hogweed (Heracleum mantegazzianum), a similar but much larger plant, is introduced and invasive. So far, this 10- to 15-foot-tall plant hasn’t been found in Minnesota, but it is present in Wisconsin, and it’s known to be especially hazardous. The Minnesota Department of Agriculture includes giant hogweed on its list of noxious weeds that should be eradicated if found. Report the plant’s location using Report a Pest or EDDMapS and handle it using extreme caution.

Invasive Plants in the Carrot Family

Cow parsnip isn’t one of Minnesota’s “bad carrots,” but several other species are, including not only giant hogweed but also wild parsnip, burnet saxifrage, Queen Anne’s lace, and several others. A guide to identifying these plants is available in the Downloads tab.



Friends of Eloise Butler Wildflower Garden

Minnesota Wildflowers

BWSR Featured Plant: Cow Parsnip

Illinois Wildflowers

USDA, NRCS. 2023. The PLANTS Database (, 06/21/2023). National Plant Data Team, Greensboro, NC USA.

Giant hogweed – Minnesota Department of Agriculture

Giant hogweed (Heracleum mantegazzianum) – Minnesota Department of Natural Resources

Friday, June 9, 2023

Plant Profile: Starflower

Starflower blooming in late May in a mixed coniferous-deciduous forest in north-central Minnesota.

Starflower (Trientalis borealis, aka Lysimachia borealis) is a spring-blooming, perennial wildflower of coniferous and deciduous forests. In early spring, stems emerge from overwintering tubers and grow 4–8 inches tall, their slender stems bearing six to eight lance-shaped leaves of unequal size. In May and June, one, two, or rarely three flowers grow from the leaf axils. Each flower is about ½ inch wide and typically has seven white, pointed petals and orange anthers that later turn brown.

The flowers are self-incompatible, so they can’t pollinate themselves. To form seeds, they must receive pollen from another patch of starflowers, delivered primarily by native mining bees (andrenid bees), sweat bees (halictid bees) and hover flies (syrphid flies). If the bees are present, if the patches are close enough for the bees to transit, and if pollination is successful, small seed capsules eventually form at the tips of the stems.

That’s a lot of ifs and little assurance of a next generation. Starflower doesn’t depend only on seeds for reproduction, however. In fact, very little of its energy is dedicated to flowering and seed set. Most of its reproductive effort is spent on rhizomes, underground stems that extend the plant’s reach and give rise to new plants. It’s a faster way of reproducing, and in a stable environment, it’s more reliable. The downside is that the parent plant and its vegetative offspring are genetically identical, so if the environment changes, the plants may not have what it takes for a population to survive.

If conditions remain favorable, though, the rhizomes grow and form patches of new plants. By midsummer, tubers begin forming at their tips. Aided by the cool nights of late summer and fall, they fill with starch to fuel next year’s growth. Rhizome connections then wither and the leaves yellow and fall. Bare stems topped with capsules are all that remain above ground, while tubers below ground carry their incipient roots and shoots through winter, ready to resume growth in spring. Starflower seeds also overwinter, but they don’t germinate until fall of the second year.

Starflower range in North America (left ) and the Upper Midwest (right). Maps from USDA Plants Database.

As with many plants, Starflower is facing challenges brought by climate change. The cool nights needed for maximum tuber development are warmer now, and researchers have found that flowering and seed set lessen toward the southern edge of the plant’s range. These changes raise questions and concerns about whether the species can adapt, because in some places, it isn't. Starflower is state-listed as endangered in Georgia and state-listed as threatened in Illinois.

Populations in Minnesota and other northern locations are responding to warmer May temperatures by flowering earlier. That may or may not be beneficial, but so far, starflower seems to be holding its own here. The species name borealis, meaning “of the north,” may be truer than ever.


Minnesota Wildflowers

Illinois Wildflowers

USDA, NRCS. 2023. The PLANTS Database (, 06/03/2023). National Plant Data Team, Greensboro, NC USA.

Roger C. Anderson. June 1970. The role of daylength and temperature in tuber formation and rhizome growth of Trientalis borealis Raf. Botanical Gazette, Volume 131, Number 2, pp. 122-128.

Roger C. Anderson and Orie L. Loucks. July 1973. Aspects of the biology of Trientalis borealis Raf. Ecology, Volume 54, Issue 4, pp. 798-808.

Roger C. Anderson and Michael H. Beare. March 1983. Breeding system and pollination ecology of Trientalis borealis (Primulaceae). American Journal of Botany, Volume 70, Issue 3, pp. 408-415.

Emily Dangremond. No date. Climate change and starflower in the Midwest. Illinois Native Plant Society.

Emily Dangremond, Christopher H. Hill, Shahd Louaibi, and Ivette Muñoz. 2021. Phenological responsiveness and fecundity decline near the southern range limit of Trientalis borealis (Primulaceae). Plant Ecology, Volume 223, pp. 41-51.  

Linda G. Chafin. 2020. Trientalis borealis Raf. Georgia Biodiversity Portal, Georgia Department of Natural Resources/Wildlife Resources Division.

Plant Profile: Wild Ginger

A single flower emerges between a pair of leaves of wild ginger, Asarum canadense . In spring, wild ginger is one of the first plants to eme...