- Scientific name: Ageratina aromatica(L.) Spach
- Species of Greatest Conservation Need (MA State Wildlife Action Plan)
- Endangered (MA Endangered Species Act)
Description
Photo Credit: Michael J. Papay
Lesser snakeroot (Ageratina aromatica) is a perennial herb of dry woodlands, rocky slopes, and barrens that depends on successional gaps in the forest canopy to thrive. It is a member of the composite family (Asteraceae) and has simple opposite leaves and white flowers that bloom from August to mid-September.
Lesser snakeroot can grow to 80 cm (2.75 ft) in height, but in Massachusetts, it is typically less than 60 cm (2 ft). The stem is hairless (glabrous) or nearly so and may be either simple or with a few branches in the upper portion. The thick, leathery leaves of lesser snakeroot are 20-90mm (0.7 -3.5 inches) long and 15-40mm (0.5-1.5 inches) wide, with short but distinct stalks. Leaf blades have three main veins running from the base towards the tip, without spines, and margins have 7-12 blunted or rounded teeth.
The inflorescence is a corymb (flat-topped open flower cluster) of discoid heads made up of small, bright white disk flowers. The hairy and leafy bracts below the heads (involucre) measure 4-4.5mm (0.15-0.17 in) long, are mostly even, in one series, and do not overlap.
The achenes—which are small, seed-like fruits characteristic of the Asteraceae family—are about 3 mm (0.1 inch), oblong, and dark in color. While the achenes are hairless (glabrous), they have a persistent pappus that creates a plume-like appearance.
Lesser snakeroot resembles the more common white snakeroot (Ageratina altissima), but lesser snakeroot has much shorter leaf stalks, more rounded teeth margins, and leaf tips that are blunt to short-pointed, compared to the long-tapering tips of white snakeroot. Other similar species in Massachusetts include bonesets (Eupatorium spp.), which generally have involucre that are uneven and overlap, and duller white flowers due to dense bristles concealing each floret.
Photo Credit: Arthur Haines, Native Plant Trust
Photo Credit: Wild Horse Native Nursery
Life cycle and behavior
Lesser snakeroot is a moderately long-lived perennial that reportedly lives for 5-10 years. It has a limited ability to spread vegetatively; however, it relies on sexual reproduction to colonize new areas and create genetically distinct individuals.
This ability to spread clonally means it is often found in small clusters of 6-10 stems in an area no greater than 10 cm (3.9 in) in diameter. Clonal stems within each cluster will grow at varying times so that each stem is at different life stages from immature to senescent. There is no indication that new clusters of genetically distinct individuals can be grown vegetatively; lesser snakeroot depends solely on seed production for the species’ long-term persistence.
In Massachusetts, lesser snakeroot flowers in August through October and each flowering stem carries as many as 1500 seeds (Craine 2003). As the plant sets seed, the darkened achenes develop side-by-side inside the involucre until the plant dries out and the bracts spread open. Each achene has a persistent pappus which catches the wind like a parachute to disperse the seeds. It is currently unknown how far the seeds of lesser snakeroot can be dispersed.
In other regions, pollination has been observed by a wide range of insects. Records include leaf-cutting bees, bumblebees, sweat bees, and potentially flower-settling moths (Johnson, 2025). In Massachusetts, however, there is no regional-specific documentation of pollinator interactions, and it is unknown whether there are specialist pollinators.
Population status
Lesser snakeroot (Ageratina aromatica) is listed under the Massachusetts Endangered Species Act as Endangered. All listed species are protected from killing, collecting, possessing, or sale and from activities that would destroy habitat and thus directly or indirectly cause mortality or disrupt critical behaviors. There are currently 2 occurrences in the state verified since 2000 found in Norfolk and Nantucket Counties. Sixteen historical occurrences which have specific locational information were in Norfolk, Nantucket, Dukes, Suffolk, and Middlesex Counties.
Distribution in Massachusetts
1999-2024
Based on records in the Natural Heritage Database
Distribution and abundance
The range of lesser snakeroot extends from Massachusetts and New York to southern Ohio, south into Florida and Louisiana. It is considered Apparently Secure or Secure from Virginia to Florida (NatureServe 2026). Massachusetts, Connecticut, New York, New Jersey, West Virginia and Ohio all consider the plant Critically Imperiled. It is considered Imperiled in Pennsylvania and has not been ranked in other states where it grows.
Southern New England is the northernmost extent of the species’ range. It is believed that this distribution is limited by photoperiod (length of day) rather than latitude or climate (Craine 2003).
Habitat
In Massachusetts, lesser snakeroot inhabits dry forest gaps, rocky slopes, south-facing rocky ledges, sandy barrens, and taluses. It is typically considered to be a perennial of early successional gap habitats created by either fire or fallen trees, and it requires a woodland dappled shade environment where it receives full to partial sun exposure.
Habitats include dry, open oak-hickory woodlands and a mowed area that was formerly scrub oak barrens. Lesser snakeroot thrives mostly in xeric or mesic habitats such as old fields, dry upland forests, and disturbed roadsides. Associated species include low heath species, scrub oak (Quercus ilicifolia), little bluestem (Schizachyrium scoparium), and numerous composites, including white wood-aster (Eurybia divaricata) and blue-stemmed goldenrod (Solidago caesia).
Healthy habitats are vital for supporting native wildlife and plants. Explore habitats and learn about conservation and restoration in Massachusetts.
Photo Credit: H. L. Abernethy
Threats
Excessive shade and over-crowding are significant threats for this species. Forest maturation and canopy closure from a lack of either natural or anthropogenic disturbance casts too much shade, while invasive and exotic plant species are prone to out-competing lesser snakeroot.
Excessive browsing by deer is a major threat that requires active management. Habitats along trails may be threatened by trampling damage during its vegetative and flowering stages.
Fire suppression is a continued threat to the long-term survival of lesser snakeroot. Additionally, habitat loss due to development and other anthropogenic use such as quarrying threaten this species.
Conservation
Survey and monitoring
In Massachusetts, the best time of year to survey for lesser snakeroot is mid-September to early October, when the flowers are mature and still present or just past. When possible, reports should include both ramets and genets, so population numbers and health can be determined. Most clusters will contain 6-10 stems of varying ages within a 10 cm (3.9 in) diameter, and the number within a cluster may be an indicator of vigor. Seed collection, when permitted, is best estimated to be done in early to mid-October.
Surveyors should take care to distinguish plants with similarities to others. Probable hybrids (intergrades) between lesser snakeroot (Ageratina aromatica)and the more common (Ageratina altissima) have been noted to occur where ranges overlap (Clewell & Wooten, 1971).
Management
Sites should be monitored for over-shading caused by forest succession. Habitat sites that do not receive enough light can be managed with canopy thinning and periodic mowing, or where applicable, prescribed burning under a low-frequency fire regime.
Management needs also include the reduction of invasive plant species. In the short-term, hand removal of competing vegetation (e.g., woody shrubs and tree seedlings) may be warranted in some populations.
The use of deer exclosures should be used to protect existing populations from browsing activity.
All active management of rare plant populations (including invasive species removal) is subject to review under the Massachusetts Endangered Species Act and should be planned in close consultation with the Massachusetts Natural Heritage & Endangered Species Program.
Research needs
Small-scale mechanical soil scarification is noted to be a possible but experimental approach to promoting germination. Additional research is needed to determine whether this approach increases germination rates or improves mean germination time.
While plants reportedly live for 5-10 years, more documentation on this species’ total lifespan is needed to verify the report (Craine 2003), particularly in the northern edge of its range.
In its southern and western ranges, lesser snakeroot has a wide range of documented pollinators from leaf-cutting bees, bumblebees, sweat bees, and potentially flower-settling moths (Johnson, 2025). While it is likely that the same or similar species pollinate lesser snakeroot where ranges overlap—and potentially similar species as those that pollinate white snakeroot—more documentation is needed for observations of general pollinator activity, as well as whether lesser snakeroot supports any specialist species.
Little is known about the plants’ natural dispersal activity and how it might inform fire management frequency. More research is needed to estimate how near the next gap must be to create suitable habitat for natural colonization to occur.
It is believed that lesser snakeroot is dependent on low-frequency fire regimes to aid in the reproductive cycle and maintain appropriate habitat based on research in more southern states (Mehlman, 1992). More research is needed to determine what exactly is the factor affecting seed production in these cases; it is possible this is a result of more open habitat and disturbance opening the canopy than a reaction to the explicit presence of fire.
Additional related research is also needed to determine patterns or associations in soil chemistry characteristics that lesser snakeroot prefers, as well as seed dispersal distance.
Previously, this species was banked in Massachusetts as a part of management planning. More research is needed to determine when and if in situ plantings should be supplemented to support existing populations. Additionally, it is unknown how long seeds remain viable.
The more common white snakeroot has been observed to have genetic differences in various ecotypes (regions). More research is needed to determine whether this is true with lesser snakeroot as well, and whether genetic provenance of New England populations is significantly different than those in the core of its distribution.
References
Ageratina aromatica in Flora of North America @ Efloras.Org. http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=220000320. Accessed 15 Apr. 2026.
Ageratina aromatica (Lesser Snakeroot): Go Botany. https://gobotany.nativeplanttrust.org/species/ageratina/aromatica/. Accessed 9 Apr. 2026.
Clewell, Andre F., and Jean W. Wooten. “A Revision of Ageratina (Compositae: Eupatorieae) from Eastern North America.” Brittonia, vol. 23, no. 2, Apr. 1971, p. 123. DOI.org (Crossref), https://doi.org/10.2307/2805429.
Craine, S.I. 2003. Ageratina aromatica (L.) Spach, lesser snakeroot Conservation and Research Plan for New England. New England Wild Flower Society, Framingham, MA
Gleason, Henry Allan, and Arthur Cronquist. Manual of Vascular Plants of Northeastern United States and Adjacent Canada. 2nd ed, New York Botanical Garden, 1991.
Gray, Asa, and Merritt Lyndon Fernald, editors. Gray’s Manual of Botany: A Handbook of the Flowering Plants and Ferns of the Central and Northeastern United States and Adjacent Canada. 8. (centennial) ed., Corrected printing, Van Nostrand, 1970.
Haines, Arthur, et al. New England Wild Flower Society’s Flora Novae Angliae: A Manual for the Identification of Native and Naturalized Higher Vascular Plants of New England. With New England Wild Flower Society, Yale University Press, 2011.
Johnson, Elizabeth A. 2025. Ageratina aromatica Rare Plant Profile. New Jersey Department of Environmental Protection, State Parks, Forests & Historic Sites, Forests & Natural Lands, Office of Natural Lands Management, New Jersey Natural Heritage Program, Trenton, NJ. 16 pp.
Magee, Dennis W., and Harry E. Ahles. Flora of the Northeast: A Manual of the Vascular Flora of New England and Adjacent New York. 2nd ed, University of Massachusetts Press, 2007.
Mehlman, David W. “Effects of Fire on Plant Community Composition of North Florida Second Growth Pineland.” Bulletin of the Torrey Botanical Club, vol. 119, no. 4, Oct. 1992, p. 376. DOI.org (Crossref), https://doi.org/10.2307/2996725.
New York Natural Heritage Program. 2026. Online Conservation Guide for Ageratina aromatica. Available from: https://guides.nynhp.org/small-white-snakeroot/. Accessed April 23, 2026.
NORM Phenology Information. Native Plant Trust, 2014.
“NYBG - New York City EcoFlora.” PDF. New York Botanical Garden, Oct. 2018, https://www.nybg.org/content/uploads/2018/09/EcoQuest_2018_October_WatchForWhiteSnakeroot_MoreInformation.pdf.
POWO (2026). "Plants of the World Online. Facilitated by the Royal Botanic Gardens, Kew. Published on the Internet; https://powo.science.kew.org/ Retrieved 23 April 2026.
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| Date published: | May 7, 2025 |
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| Last updated: | May 14, 2026 |