Linnaeus published the genus Thalia in 1753, in his Species Plantarum, for a group of tall, broad-leaved perennial plants that grow rooted in shallow water, among them Thalia dealbata, commonly called hardy canna or powdery alligator-flag, valued today by gardeners for ornamental water gardens and by ecologists for its role in wetland habitats. The name is not, despite the coincidence of spelling, a tribute to the Muse of comedy, or to the Grace who shares her name. Botanical reference works that document Linnaean eponymy, among them the Missouri Botanical Garden's own record of Thalia dealbata, agree that Linnaeus instead honored Johannes Thal, a German physician who died in 1583. Thal spent years cataloguing the plants of the Harz mountains, and the flora he compiled, Sylva Hercynia, was published after his death in 1588 by Joachim Camerarius the Younger; historians of botany credit it as one of the earliest works to describe the full plant life of a specific region rather than only its medicinal species.
The same surname produced the identical confusion once already. The mustard family plant that became the standard model organism of plant genetics, Arabidopsis thaliana, carries a species name that also honors Thal rather than the Muse, and for the same reason: he was the first to describe the plant, in the same Sylva Hercynia. Thalia the Muse of comedy and pastoral poetry has, despite the two names that echo her, no plant named for her own mythological character; both belong instead to the physician who shares her name by coincidence of Latin form.
Sources Missouri Botanical Garden Plant Finder: Thalia dealbataMissouri Botanical Garden with Deutsche Biographie: Johann ThalHistorische Kommission bei der Bayerischen Akademie der Wissenschaften