Vascular Plants of North Carolina
Account for Deepwoods Horsebalm - Collinsonia tuberosa   Michaux
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Section 6 » Order Lamiales » Family Lamiaceae
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AuthorMichaux
DistributionWidely scattered over most of the Piedmont, north only to Alamance, Guilford, and Davie counties, and in the southeastern mountains. As this species is not known from VA, the species is probably truly absent from the extreme northern Piedmont and northern mountains. It does not occur in the Coastal Plain.

This is a globally scarce species of the Southern states, ranging from central NC and western TN south to southern AL and LA.
AbundanceRare in the southern Piedmont and adjacent southeastern mountains, from Montgomery and Richmond counties west to McDowell and Henderson counties. Very rare north to Chatham, and Davie counties, where probably mostly of historical occurrence. This is a State Special Concern species. The NCNHP has 18 records, but only about half of these are current, and only about one-half dozen are anything other than of poor quality. Thus, the S1 State Rank seems justified, as this species is not faring well at all in NC.
HabitatThis is a species that requires high pH soil, in moist and shaded conditions. Thus, most sites are in Basic Mesic Forests, but a few might be in Basic Oak-Hickory Forest or in adjacent rich bottomland forests.
See also Habitat Account for Rich Wet-Mesic Hardwood Forests
PhenologyBlooms from late July to September, and fruits in September and October.
IdentificationThis is a medium-sized herb, somewhat shorter and less robust than the similar C. canadensis, to which it needs to be carefully compared with. This species is mostly unbranched, growing to about 2' tall, with a few pairs of opposite leaves on quite long petioles. Note that the petioles in C. tuberosa are at least half as long as the blade; that is, the petiole averages nearly 2" long, and the ovate to elliptic blade is only about 3" long and 2" wide, with serrated margins. The terminal panicle of scattered flowers in a pyramid shape is about 4-6" long, but in this species the flowers are white to cream in color, paler than the canary yellow in C. canadensis. Note that both species can theoretically grow in the same area on the same slope, and bloom at the same time; but this species is quite rare and extremely difficult to find without knowing where to look. Experienced biologists can probably identify the species just in vegetative condition, owing to the long petiole that is generally more than half as long as the length of the blade. In fact, very few people have seen the species in bloom in NC.
Taxonomic CommentsWeakley (2018) mentions that a fairly recent paper concludes that the species should be merged with C. canadensis, but hardly any reference abides by this.

Other Common Name(s)Stoneroot, Tuberous Horsebalm
State RankS1
Global RankG3G4
State StatusSC-V
US Status
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