Positive patch test reactions to Frullania nisquallensis were observed in seven forest workers who had allergic contact dermatitis. Frullania is a genus of leafy liverworts. Five of these seven patients also showed coincidental positive patch test reactions to usnic acid derived from lichenized fungi. Attacks of such dermatitis occurred only during work in forest areas, were worse in wet weather, appeared within a day or two of starting work amongst vegetation, and subsided in two to four weeks after leaving work. "Cedarpoisoning" is a misnomer for allergic contact dermatitis occurring in forest workers in British Columbia; such dermatitis results from exposure to species of epiphytes on trees.
Mitchell JC, Schofield WB, Singh B, Towers GHN. Allergy to FrullaniaAllergic Contact Dermatitis Occurring in Forest Workers Caused by Exposure to Frullania nisquallensis. Arch Dermatol. 1969;100(1):46-49. doi:10.1001/archderm.1969.01610250052012