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Acmispon helleri by Hugh and Carol Nourse. Image may be subject to copyright.
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Acmispon helleri (Britton) A.A. Heller

Carolina Trefoil

Federal Protection: No US federal protection

State Protection: Endangered

Global Rank: G5T3

State Rank: S1

SWAP High Priority Species (SGCN): Yes

Element Occurrences (EOs) in Georgia: 4

Habitat Summary for element in Georgia: Clayey soil over ultramafic rock; post oak-blackjack oak savannas


Annual herb with erect, leaning, or trailing stems up to 30 inches (75 cm) long; the main stems are reddish with strongly two-ranked side branches; both stems and branches are usually hairy. Most of the leaves have 3 narrow, pointed leaflets, 0.2 - 0.7 inch (0.5 - 1.8 cm) long and less than 0.2 inch (0.5 cm) wide; the uppermost leaves have only 1 leaflet. The flowers are less than 0.3 inch (0.8 cm) long, pink, with an erect banner petal and 2 wing petals enclosing a yellowish keel petal; the flowers are usually solitary on a stalk up to 0.8 inch (2 cm) long that arises in the angle between leaf stalk and stem. Fruits are narrow pods up to 1.4 inches (2 - 3.5 cm) long.

Similar Species

Milk-pea (Galactia volubilis), also a trailing vine with pink flowers in the pea family, occurs in the same habitat as Carolina Trefoil. It has oval leaflets with blunt or rounded tips; its flowers are usually held in an elongated cluster.

Related Rare Species

None in Georgia.


Openings in Post Oak and Blackjack Oak woodlands with Iredell clay soils, over bedrock high in iron and magnesium, such as ultramafic rock; clearings, lawns, roadsides, and rights-of-way through these habitats.

Life History

Carolina Trefoil, also treated either as Lotus helleri, Acmispon helleri, or Lotus unifoliolatus var. helleri, is an annual herb that reproduces sexually by seed; it does not spread vegetatively. As with most members of the pea family, Carolina Trefoil flowers are probably pollinated by bees, which are attracted to nectar and to the showy banner petal and are heavy enough to trigger the pollination process. The pollination mechanism in Lotus / Acmispon species differs from most other pea family flowers where bees force the wing and keel petals apart and are dusted with pollen while they search for nectar. In Lotus / Acmispon, pollen accumulates in the end of the keel petal; when the wing petals and keel petal are weighed down by a bee, a sticky ribbon of pollen is forced out of a hole in the tip of the keel and onto the underside of the bee. The ribbon of pollen is then carried to another flower by the bee, where it is transferred to the stigma. Lotus / Acmispon flowers usually require cross-pollination to set fruit and viable seed although some researchers have observed seed set following self-fertilization. As an annual, Carolina Trefoil is dependent on the production of viable seed to survive.

Survey Recommendations

Surveys are best conducted during flowering (late August–September) and fruiting (August–October).


Piedmont of Georgia, South Carolina, North Carolina, and Virginia. It is rare throughout its range.


Conversion of habitat to pine plantations, pastures, farmland, and residential and commercial development. Encroachment by woody species in the absence of fire.

Georgia Conservation Status

Acmispon helleri is ranked S1 by the Georgia Department of Natural Resources, indicating that it is critically imperiled in Georgia. Four populations have been observed in Georgia since 1949. Only two populations have survived, one of which is on conservation land.

Conservation Management Recommendations

Avoid logging and mechanical clearing. Hand-clear or use fire to create openings in dry woodlands.


Chafin, L.G. 2007. Field guide to the rare plants of Georgia. State Botanical Garden of Georgia and University of Georgia Press, Athens.

GADNR. 2020. Element occurrence records for Acmispon helleri. Georgia Department of Natural Resources, Wildlife Resources Division, Social Circle, Georgia.

Isely, D. 1978. New varieties and combinations in Lotus, Baptisia, Thermopsis, and Sophora  (Leguminosae). Brittonia 30(4): 466-472. https://www.jstor.org/stable/pdf/2806352.pdf?refreqid=excelsior%3A6e16cf508eb0638794ab24c05a958094

Isely, D. 1990. Lotus purshianus var. helleri species account. Vascular flora of the southeastern United States, Vol. 3, Leguminosae (Fabaceae). University of North Carolina Press, Chapel Hill.

Masson, R. and J. M. Stucky.  2008. Lotus unifoliolatus var. helleri phenology and response to simulated mowing. Journal of the North Carolina Academy of Science 124: 6-10. https://www.jstor.org/stable/24336037

NatureServe. 2019. Lotus unifoliolatus var. helleri comprehensive report. NatureServe Explorer. Arlington, Virginia. http://explorer.natureserve.org/servlet/NatureServe?loadTemplate=tabular_report.wmt&paging=home&save=all&sourceTemplate=reviewMiddle.wmt

Proctor, M., P. Yeo, and A. Lack. 1996. Natural history of pollination. Timber Press, Portland, Oregon.

Radford, A.E., H.E. Ahles, and C.R. Bell. 1968. Manual of the vascular flora of the Carolinas. University of North Carolina Press, Chapel Hill.

Richards, K.W. and Friesen, K.R.D. 2001. Basic pollination requirements of five Lotus species. Acta Horticulturae (ISHS) 561:333-337. http://www.actahort.org/books/561/561\_51.htm. https://www.actahort.org/members/showpdf?booknrarnr=561_51

Tompkins, R.D. and J.M. Stucky. 2000. Microhabitat study of Lotus unifoliatus var. helleri: microdistribution, associated species, and potential effects of roadside mowing. Castanea 65(3): 213-220. https://www.jstor.org/stable/pdf/4034089.pdf?ab_segments=0%252Fbasic _SYC-5055%252Ftest&refreqid=excelsior%3A519fac38b8d7166fcf146158e3cf29b2

Weakley, A.S. 2015. Flora of the southern and mid-Atlantic States. University of North Carolina Herbarium, University of North Carolina, Chapel Hill. http://www.herbarium.unc.edu/flora.htm

Authors of Account

Linda G. Chafin

Date Compiled or Updated

L. Chafin, May 2007: original account

K. Owers, Feb. 2010: added pictures

L. Chafin, March 2020: updated original account

Acmispon helleri, illustration by Jean C. Putnam Hancock. Image may be subject to copyright.
Acmispon helleri by Hugh and Carol Nourse. Image may be subject to copyright.
Acmispon helleri by Hugh and Carol Nourse. Image may be subject to copyright
Acmispon helleri by Alan Cressler. Image may be subject to copyright.