Readers have asked what the tall, yellow flowering plants are growing along the roadside in the same vicinity as poison hemlock. Though there are many yellow flowering plants this time of year, the two most visible from the windshield would be yellow sweetclover and wild parsnip.
A yellow flower, biennial life cycle and height of the flower stalk are the only things these two plant species have in common. Sweetclover is a member of the legume/bean family, and wild parsnip is a member of the carrot/parsley family.
Sweetclover, Melilotus officinali (L.) Pall, is not even in the same genus as the true clovers (Trifolium ssp.). Its architecture and leaves are more like alfalfa. The sweet part of its name comes from the smell of the forage caused by the chemical coumarin, which can convert to a toxic anticoagulant, dicoumarin.
Sweetclover is a non-native plant brought in by early settlers from Europe as a hay and green manure crop. It is known as an excellent nectar source for honey bees.
Sweetclover plants complete their life cycle in two years. Flowers are produced the second year on the upper part of three to five feet tall stems. Single flowers are formed along a central stalk that contain four petals (called a banner, keel, and two wings) that have a unique shape associated with plant flowers of the legume family.
Livestock producers who grow hay that contains sweetclover must make sure plants are properly dried and cured to prevent the production of dicoumarin. The toxin is generally produced when cut sweetclover plants become moldy and then baled for hay, which may then may cause bleeding disease in animals.
Both yellow and white sweetclover are on the Ohio Invasive Plants Council’s invasive plant list. One sweetclover plant can produce over 100,000 seeds, which can remain viable for 30 years. During the second year of growth, sweetclover plants may outcompete native plants for sun, water, and nutrients.
The other plant that may be found with a yellow flower along field edges and roadways at this time is wild parsnip, Pastinaca sativa L. Plant and leaf shape will be similar to poison hemlock except wild parsnip is generally somewhat shorter and the leaves have a more green-yellow coloration. Poison hemlock flowers will not be yellow, but white.
Like other members of the carrot family, plants generally live for two years growing as a rosette the first year and producing a three to five foot stem with flowers the second year. Clusters of flowers (called umbels) are arranged in a way that resembles small umbrellas. Individual flowers are small and have five petals.
Wild parsnips are the same plants as those grown in gardens except they have escaped the cultivated area. The edible tap root in the garden develops during the first year of growth. However, an individual should avoid harvesting these wild roots since they may confuse the plant with poison hemlock, which are toxic and may cause death.
Parsnips also produce a toxin that may irritate the skin but does not cause death. The sap or plant juices contain the chemical compound called furanocoumarin. Furanocoumarin reacts to sunlight on the skin and may cause a chemical burn similar to sunburn.
The level of burn depends on the amount of the chemical on the skin. Its effects may range from redness of skin to painful blisters (similar to first and second degree sunburn). The burning effects may occur from a relatively short exposure to sunlight. The skin will become discolored (dark brown) and remain that way for over a year in some cases.
People inadvertently may come in contact with parsnip sap as a result from walking among plants along the roadway, hunting for a lost golf ball, or chasing an escaped pet. Other cases occur while mowing or using weed trimmers.
The key to protection is not exposing bare skin to the sap — wear shirts with long sleeves and pants and shoes rather than shorts and sandals. Thus when working in areas of wild parsnips (or any parsnip):
• Keep arms and legs covered with long sleeves and pants
• Work with the plant on cloudy days and wash your skin immediately if contact has been made with plant sap
• Wear eye/face protection along with long sleeve shirt, pants, and gloves when mowing or using a weed trimmer
• Be careful not to touch your face or bare skin since hands may have come in contact with contaminated clothing
• Wash skin immediately if skin comes in contact with plant sap
• Protect skin for 48 hours from sunlight that may have been in contact with plant juices
Animals and livestock fur or hide will protect them but they are also susceptible if the plant juices come in contact with bare skin. Also individuals may come in contact with the sap if animals have been running through a parsnip area and get sap or juices on their fur.
It is important to know the different plant species when outdoors. More information may be found on sweetclover and wild parsnip at the following websites: http://bygl.osu.edu/node/775; https://www.agry.purdue.edu/ext/forages/publications/ay233.htm; and http://www.oipc.info/uploads/5/8/6/5/58652481/16factsheetwhiteyellowsweetclovers.pdf
Lentz is extension educator for agriculture and natural resources for The Ohio State University Extension Service in Hancock County. He can be reached at 419-422-3851 or via email at firstname.lastname@example.org.
Lentz can be heard with Vaun Wickerham on weekdays at 6:35 a.m. on WFIN, at 5:43 a.m. on WKXA-FM, and at 5:28 a.m. at 106.3 The Fox.
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