Vascular Plants of North Carolina
Account for Whorled Horsebalm - Collinsonia verticillata   Baldwin
Members of Lamiaceae:
Members of Collinsonia with account distribution info or public map:
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Section 6 » Order Lamiales » Family Lamiaceae
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DistributionLimited essentially to Polk County, in the southwestern Piedmont and along the Blue Ridge Escarpment. There are SERNEC specimen records for Madison, Macon, and Ashe counties, but this website maps only NCU specimen, with the caveat that the plant is vegetative and needs to be carefully checked for ID. The Ashe specimen (GAS) had flowers in late September and thus is discounted; the Macon "specimen" (CLEMS) is actually a report from late August and is also discounted. The iNaturalist website has several photos from Buncombe County. Finally, the NCNHP has a vegetation plot report for Burke County, a plausible location, but for such a rare species in the state, a specimen or photos are needed; vegetation plot data have often produced spurious sight reports of rare species. Note that VA has recent records for two counties just over the state line along the northeastern Piedmont (near Kerr Lake); thus, the species might eventually be found elsewhere in the NC Piedmont.

This is a Southern species with many tightly local and disjunct populations. It is mainly found from eastern TN and southwestern NC south to central GA and southern AL; disjunct to southern VA and southern OH.
AbundanceUncommon in Polk County, with close to 12-13 current records. Extremely rare elsewhere, and that is confirmed only for Madison County. This is a State Threatened species. Though practically limited to just one county, the NCNHP State Rank of S2 is correct, as there are certainly between 6-20 current populations. Though C. tuberosa has been recorded from many more counties in NC (a dozen or more), very few populations of it remain, and it has a State Rank of S1S2.
HabitatAs with other Collinsonia species in NC, this species requires high pH soil, normally where rich and rather moist. Most sites in Polk County are in Basic Mesic Forests. It can be found in somewhat drier sites, perhaps in Basic Oak-Hickory Forests.
PhenologyUnlike the other two species in the genus, this is a spring blooming one, flowering from late April to early June; fruits in June and July.
IdentificationThis is a medium-sized herb growing to about 1.5 feet tall, with an unbranched stem. It has several pairs of opposite leaves, but the top two are located just below the inflorescence and close together, appearing like a whorl of 4 leaves. Each leaf is elliptical to more often widely ovate, about 5-6 inches long and about half as wide, with a short petiole and serrated margins. The terminal raceme or narrow panicle is about 4-6 inches long and contains numerous pink or pinkish-white flowers, each about 3/4-inch long, with a long lower lip and the stamens and pistils extending far beyond the corolla. Thus, this species differs completely from the other two Collinsonia species, mostly by the upper pair of leaves being essentially in a whorl of 4 leaves, and the flowers being pinkish in color. This species is not overly difficult to find on rich slopes in Polk County, but elsewhere, it is practically absent. However, considering that there are a few specimens from elsewhere and a few vegetation plot reports from elsewhere, all of which need to be confirmed, new discoveries of this species in NC are almost certainly "out there".
Taxonomic CommentsNone

Other Common Name(s)Stoneroot, Early Stoneroot
State RankS2
Global RankG3G4
State StatusT
US Status
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