By David D. Taylor, US Forest Service
Blue mistflower is a late summer to frost flowering species frequently encountered in Kentucky. It is a member of the sunflower family (Asteraceae) and belongs to what is known as the tribe Eupatorieae. This tribe includes some well-known genera including Eupatorium (thoroughworts), Eutrochium (Joe pye-weeds), Ageratina (snakeroots) and Ageratum (the cultivated ageratums).
A name change
Blue mistflower was described and named by Linnaeus in 1753 as Eupatorium coelestinum. Swiss botanist A.P. de Candolle determined it was worthy of its own genus and named the plant Conoclinium coelestinum in 1836. The name was not widely accepted and Eupatorium coelestinum was used well into the 1900s by various botanists. That name can be found in floras and manuals such as Gleason (1952, p. 493), Correll and Correll (1970, pp. 1555–1556), Fernald (1970, p. 1370), and Gandhi and Thomas (1989, p. 78).More recent research, including genetic analysis, supports the separate genus Conoclinium. More recent manuals and floras (e.g., Wunderlin 1982, p. 370; Jones 2005, p. 225; Patterson and Nesom 2006, p. 480; Weakley et al. 2023, p. 1635) use that name.
Four species are found in the eastern, central and southwestern U.S. and northern Mexico. Blue mistflower, is the only species in Kentucky. Another similar species, Pink thoroughwort (Fleischmannia incarnata) is also in Kentucky and the two species are sometimes confused (see below).
The genus name is derived from the Greek words κῶνος (kônos), meaning cone, and κλινίον (kliníon), meaning little bed. The words refer to the shape of the receptacle, the small pad of tissue on which the flowers and fruits are borne in each tiny head of flowers. The specific epithet is derived from the Latin caelistis (also spelled coelestis) meaning celestial or heavenly, in reference to the often-sky-blue color of the flowers.
Culture and botany
It typically grows in moist soil, often along ditches, streambanks, moist disturbed areas, moist shady patches in forest, and less commonly, in drier sunnier locations. It will grow on basic (sweet) to somewhat acid soils. When in ideal growing conditions, plants may reach 2.5 feet (76 centimeters) tall and nearly as wide. Patches of plants can create a ground cover. Leaves are strongly wrinkled ovate to deltoid to triangular, up to 2 inches (5 centimeters) long and almost as wide near the base. They are medium green above and lighter below.
Plants are much branched, with each branch ending in a flat-topped to slightly rounded cluster of generally purplish-blue to light blue, but sometimes pinkish blue flower clusters. Within each cluster is 10–25 flower heads (also called capitula).
Because the plant is in the sunflower family, what may look like a single flower is actually a group (heads, or capitula) of very small flowers. Each head can contain 30–50 individual flowers. All of the flowers are tubular disk flowers. There are no ligulate (strap-shaped) flowers like the ones on a sunflower. The flowers appear fuzzy because the styles/stigmas extend 0.25” or more out of the flower.
This species is cultivated as a garden in many areas. It does especially well in partial shade where soils are moist to average in either gardens or natural settings. Large patches of the plant in flower are striking because of the intense blue to purplish color. Flowers can last for 2–3 weeks depending on temperature and rainfall. The plant will also grow in full sun and in drier soils. It tends to be short in such locations and does not flower for long. It also tends to look somewhat scrappy in these locations.
A number of commercial nurseries sell seed and plants. You may also be able to collect seed from along a road ditch somewhere. It is best to find a source close to where you intend to plant the seed or plants rather than purchasing from many states away. Blue mist flower is a perennial and if growing conditions are suitable, the plant will come back for several year before dying. Allow at least some of the seed to fall to establish replacement plants and increase the size of the patch.
Like many of the species related to Eupatorium, blue mistflower is a copious nectar producer and attracts butterflies of many species. When in more open areas, monarchs will spend a lot of time feeding on this plant, especially if near milkweeds. Small bees such as jewel bees will sometimes visit the flowers as well. Occasionally honeybees and bumble bees will take nectar from the flowers.
A related plant, pink thoroughwort, is sometimes confused with blue mistflower. This species tends to have long stems (up to 6 feet or so), but stems are lax, sprawling on other plants or the ground. Scattered branches are relatively few, short, and often in the same plane as the main stem. Leaves, 2–3.5 inches long, are triangular to deltoid with somewhat tapering tips (see photos below). Flowers look similar to blue mistflower, but are usually pink-purple or whitish with pink or lavender lobes.
Pink thoroughwort usually grows where limestone is close the surface and soils are moist, such as along creek banks, thickets, open forest, and bottomland fields. The species has a range similar to, but narrower than blue mistflower: from Missouri east to Ohio and Virginia, south to Florida, then west to Texas and Oklahoma. USDA-NRCS (2023) adds Arizona (but probably an error per Nesom 2006, p. 541). Weakley et al. (2023, p. 1666) adds northeastern Mexico. In Kentucky, the species is mostly in the Bluegrass counties between Lexington and Louisville, and in scattered in the Jackson Purchase counties, with outliers in Bell, Floyd, Pike, Pulaski and Wayne counties. The two species may grow together.
This plant also attracts butterflies, at least when in open bottomland areas. Plants in open forest situations are often close to the ground and larger butterflies do not find the flowers. Small butterflies and some bees will visit them. It does not make for a great garden plant, but does well in natural settings.
Range
The species’ range is New York State south to Florida, then west to Texas, north to Nebraska and Missouri, through Illinois to Michigan. Patterson and Nesom (2026) and USDA-NRCS (2023) add Ontario, Canada, the latter source indicating it is introduced there. BONAP (2014) shows the same states, but adds Iowa. Both BONAP (2014) and Weakley et al. (2023) indicate New York plants are likely escapees from cultivation.
USDA-NRCS (2023) shows it from 91 counties in Kentucky from far western counties to most of the eastern counties. BONAP (2014) shows approximately the same distribution in Kentucky. In all likelihood, the blue mistflower is in every Kentucky county.
References
[BONAP] Biota of North America Program. 2014. North American Plant Atlas. Conoclinium coelestinum. Available at http://bonap.net/MapGallery/County/Conoclinium%20coelestinum.png. Accessed 6 October 2023.
Correll, D.S. and M.C. Johnston. 1970. Manual of the vascular plants of Texas. Contributions from Texas Research Foundation, Volume 6. Texas Research Foundation. Renner, TX. 1881 p.
Gandhi, K.N. and R.D. Thomas. 1989. Asteraceae of Louisiana. Sida, Botanical Miscellany, No. 4. Botanical Research Institute of Texas. Dallas, TX. 202 p.
Gleason, H.A. 1952b. The new Britton and Brown illustrated flora of the Northeastern United States and adjacent Canada. Volume. 3. Hafner Press. New York, NY. 594 p.
Fernald, M.L. 1970. Gray’s manual of Botany. Eighth edition, Corrected printing. Van Nostrand Company. New York, NY. 1632 p.
Jones, R.L. 2005. Plant life of Kentucky: An illustrated guide to the vascular flora. The University Press of Kentucky. 834 p.
Patterson, and G.L. Nesom. 2006. Conoclinium coelestinum. P. 480. IN: Flora of North America Committee. 2006. Flora of North America. Vol. 21. Magnoliophyta: Asteridae (in part): Asteraceae, part 3. Oxford University Press. New York, NY. 616 pp. Available at http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=220003245 Accessed 6 October 2023. (See also the friendlier page at http://beta.floranorthamerica.org/Conoclinium_coelestinum. Accessed 6 October 2023.
Nesom, G.L. 2006. Fleischmannia incarnata. P. 541. IN: Flora of North America Committee. 2006. Flora of North America. Vol. 21. Magnoliophyta: Asteridae (in part): Asteraceae, part 3. Oxford University Press. New York, NY. 616 pp. Available at. Available at http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=250066778 6 October 2023. (See also the friendlier page at http://beta.floranorthamerica.org/ Fleischmannia_incarnata. Accessed 6 October 2023.)
[USDA-NRCS] U.S. Department of Agriculture, Natural Resources Conservation Service. 2023. Plants Database, an online application. Available at https://plants.usda.gov/home/plantProfile?symbol=COCO13 (blue mistflower); and https://plants.usda.gov/home/plantProfile?symbol=FLIN2 (pink thoroughwort). Accessed 6 October 2023.Weakley, A.S. and the Southeastern Flora Committee. 2023. Flora of the Southeastern United States. Edition of 14 April 2023. University of North Carolina at Chapel Hill, NC. 2015 p. Available at https://ncbg.unc.edu/research/unc-herbarium/flora-request/. Downloaded 9 May 2023.
Wunderlin, R.P. 1982. Guide to the vascular plants of Central Florida. University Presses of Florida. Gainesville, FL. 472 p.
All Photos by author.
David Taylor, Forest Botanist for the Daniel Boone National Forest for the last 34 years, works with rare plants, invasive plants and plants in general. Most of his hiking and plant observations occur in the eastern and east-central parts of Kentucky. He encourages native plants and works to remove invasive plants on his property in central Kentucky.