Species Profile: Ironweeds | Vernonia spp.

Scientific Name: Vernonia spp.
Common Name (s): Ironweeds

Arkansas Ironweed – Vernonia arkansana
Photos by Kayla Sayre, Bella Vista POA Fisheries & Water Quality Sr. Technician

Identification:

Ironweed is a genus in the family Asteraceae which also includes asters, sunflowers, and daisies. Ironweed has fuzzy or puffed flowers that are dark purple and sometimes magenta. Secondary stems come off the primary stem and branch continuously to form florets or flowers. There are 50 to 120 flowers per plant. Most, but not all, species in this genus have fuzzy hair covering their leaves and stems, which may make them look green gray from various angles. The leaves are simple and pinnate and are arranged alternately, or in a spiral, around the stem. Some species in this genus have toothed margins along the leaves but may be smooth depending on their distribution. The stem produces a milky sap when broken. There are eighteen species in this genus in North America, with eight species found in Arkansas.

One notable and easily identified species in this genus is the Arkansas ironweed or curly-top ironweed. It can grow to heights of 4 to 6 feet and widths of 3 to 4 feet. It is easily identified by the curly, thin, hair-like green-gray involucre (or whirled) bracts. Involucre bracts are located at the flower head and surround the base of the petals. Arkansas Ironweed is smooth and hairless. It has leaves that are narrow and toothed.

Arkansas Ironweed Range
https://plants.usda.gov/home

Range:

Ironweeds are found throughout the United States. The Arkansas Ironweed has an extensive distribution found in Arkansas, Oklahoma, Kansas, Missouri, Illinois, Wisconsin, Indiana, Ohio, and New York.

Ecology:

Interestingly, if different species of ironweed grow near one another, they will interbreed. Arkansas ironweed often hybridizes with western ironweed or prairie ironweed. This means some wild ironweed plants are a random combination of characteristics from each species.

Arkansas ironweed can spread through seeding in favorable conditions. Arkansas ironweed prefers soil that stays consistently moist. It can grow to its max height and width if the soil moisture is favorable. They prefer conditions with high light and moderate soil fertility. They are found in sunny habitats, such as gravel or sand bars, glades, prairies, open woods, rocky slopes, tickets, and meadows. If conditions are unfavorable for seed development, they will spread by rhizomes. They can form dense clumps and spread aggressively by rhizomes and aggressively by seed if soil conditions are favorable.

Arkansas ironweed is a great low-maintenance native to add to any pollinator garden. Arkansas ironweed blooms between July and October. Their blooms attract pollinator insects such as bees, butterflies, and skippers.  Melissodes vernoniae, a long-horned bee, pollinates exclusively on ironweed species.  Similarly, the aphid Aphis vernoniae exclusively feeds on the sap of Arkansas ironweed. Most importantly, Arkansas ironweed and other species in this genus are deer resistant and avoided by most herbivorous mammals due to their bitter taste.

Special Notes:

In Bella Vista, ironweed species are found along the roads and on hillsides. Additionally, they can be found along stream banks and lakeshores. They bloom from late July to early August in Northwest Arkansas. Historically, ironwood tea made from leaves was used to relieve pain from childbirth and fever.