Battling invasion by five prohibited plant species
This season we are continuing our work to map, manage and contain populations of five NR-40 listed plant species that have invaded our 8-county region:
Wild chervil (Anthriscus sylvestris) (left) is an herbaceous biennial that grows up to 3.25 feet with hollow stems that are covered in hairs. Plants grow aggressively to out-compete native vegetation and are forming extensive stands in Ozaukee, Sheboygan and Washington Counties.
Lesser celandine (Ranunculus ficaria) (right) grows as an herbaceous groundcover with kidney to heart-shaped leaves and yellow buttercup flowers. Plants appear soon after snow melt and rapidly spread into new areas. After flowering in March and April, plants die back by June providing a very narrow window in which to search, identify and control this invader which is spreading in Milwaukee, Racine, Kenosha, Walworth and Washington Counties.
Hairy willow herb (Epilobium hirsutum) (left) is a semi-aquatic perennial herb that grows 3-6 feet tall, with fine, soft hairs covering the entire plant. Tall, branching stems form dense, monotypic stands that can be found in open riparian areas along streams, ditch banks, wetlands and moist waste places. The plant is flood tolerant and spreads by seeds and stolons, which develop into rhizomes after growing into the ground. The rhizomes branch extensively, and are growing up to 2 meters in length in Kenosha, Racine and Sheboygan Counties.
Giant hogweed (Heracleum mantegazzianum) (right) is an herbaceous biennial or monocarpic perennial that grows as a bushy rosette the first year, and then bolts during the second year to 8-20 feet tall. The hollow, ridged stems are covered in coarse white hairs and reddish-purple mottling. Leaves are compound, 1 to 5 foot wide, palmate, deeply lobed and pointed. Flowers are large flat-top umbels, up to 20 inches wide, with white, 5-petaled flowers that bloom from May-July. To-date giant hogweed has been contained in Sheboygan County. Sap from giant hogweed plants can cause severe burns and blisters!
Manchu Tubergourd (Thladiantha dubia) (left), also known as golden creeper, is a perennial herbaceous 6 to 20 foot vine with showy, bright yellow flowers that bloom from July to September. Leaves are ovate with a heart-shaped base and stems are slender, climbing over other vegetation by means of tendrils. Plants reproduce by very persistent, widely spreading, fleshy, underground, potato-like tubers, making the species extremely difficult to eradicate in Waukesha County.