Perityle is a genus of flowering plants in the daisy family (Asteraceae), order Asterales, commonly known as rock daisies. It is a morphologically variable group whose members range from small annual or perennial herbs to spreading shrubs. Most species produce yellow or white daisy-like flower heads, and the fruit is generally a flat, achene-like seed with thickened margins that may or may not bear a pappus or scales. The genus is native to North and South America, with its greatest diversity in the arid and semi-arid regions of the southwestern United States and Mexico.
The circumscription of Perityle has changed substantially in recent years. A 2022 study combining morphological, cytological, and phylogenomic analyses of chloroplast and nuclear genomes found that the genus as previously defined was polyphyletic. In response, the authors revived and expanded the related genera Galinsogeopsis, Laphamia, and Nesothamnus to establish monophyletic groupings. At the same time, the small genus Amauria and the Desventuradas Islands endemic species Lycapsus tenuifolius were merged into Perityle, leaving the genus with 13 currently accepted species.
Distribution
Perityle is native to North and South America, with members found primarily in arid and semi-arid habitats. The common name "rock daisies" reflects their frequent occurrence on rocky terrain in the southwestern United States and adjacent Mexico.
Taxonomy Notes
Perityle as previously circumscribed was shown to be polyphyletic by a 2022 phylogenomic study. This led to the revival and expansion of Galinsogeopsis, Laphamia, and Nesothamnus, while Amauria and Lycapsus tenuifolius (a Desventuradas Islands endemic) were subsumed into Perityle, reducing the genus to 13 accepted species. Several former Perityle species are now placed in Laphamia (e.g., Laphamia fosteri, Laphamia inyoensis, Laphamia lindheimeri, Laphamia saxicola) and Nesothamnus (e.g., Nesothamnus incanus).
