Trichostema coeruleum (Michaux) K.S. McClelland & Weakley. Section: Isanthus. Common name: Glade Blue Curls, False Pennyroyal. Phenology: (Jul-) Aug-Sep (-Oct). Habitat: Shale barrens, outcrops of calcareous or mafic rock, diabase barrens, calcareous dry prairies, disturbed rocky areas. Distribution: VT and s. ON west to MN and NE, south to c. and w. NC, nc. SC, nw. GA, AL, MS, TX, and AZ.

Origin/Endemic status: Native

Taxonomy Comments: As explained in McClelland & Weakley (2023), the lectotype illustration of T. brachiatum L. (Dillenius 1732) is actually an illustration of T. dichotomum L., meaning that these two names are synonyms. The earliest name for the species previously referred to as T. brachiatum is Isanthus coeruleus Michx. (Michaux 1803). Given that genetic evidence shows that this species should be included in the genus Trichostema (McClelland 2022; McClelland et al. 2023), McClelland & Weakley (2023) made the new combination Trichostema coeruleum K.S. McClell & Weakley.

Synonymy ⓘ: = McClelland & Weakley (2023) in Weakley et al (2023); = Isanthus brachiatus (L.) Britton, Sterns, & Poggenb. — C, F, Il, S, Tn, WV; = n/a — RAB, Tat; = Trichostema brachiatum L. — Ar, GrPl, K4, Mi, Mo3, NcTx, NE, NY, Pa, Tx, Va, W, Lewis (1945); > Isanthus brachiatus (L.) Britton, Sterns, & Poggenb. var. brachiatus — G; > Isanthus brachiatus (L.) Britton, Sterns, & Poggenb. var. linearis Fassett — G; Isanthus coeruleus Michx. Basionym: Isanthus coeruleus Michx. 1803

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