Crocanthemum Spach. Common name: Frostweed, Rockrose.

Key to Crocanthemum

A genus of about 24 species, of eastern North America, California, Mexico, and s. South America. The eastern North American species previously attributed to Helianthemum are in a clade distinct from the Old World Helianthemum, and should be recognized as Crocanthemum.

Key advice:The identification of most of our species of Crocanthemum requires an understanding of the 2 types of flowers produced. Chasmogamous flowers have showy yellow petals and larger sepals, the distinct portion of the 2 linear outer sepals usually linear, (0.7-) 1.3-5.5 mm long, the distinct portion of the 3 broader inner sepals 2.5-12 (-14) mm long. Cleistogamous flowers lack petals and have smaller sepals, the distinct portion of the 2 linear outer sepals 0.2-3 mm long, the distinct portion of the 3 broader inner sepals 1.5-4.8 mm long. In some species (C. canadense, C. bicknellii, C. propinquum) the chasmogamous flowers open earlier (Apr-Jul) than the cleistogamous (Jun-Sep). In others (C. corymbosum, C. georgianum, C. nashii, C. rosmarinifolium), the two types of flowers open at the same time (Mar-Jun) or cleistogamous flowers are nearly always absent (C. carolinianum). Capsules from chasmogamous flowers are larger and contain more seeds than those from cleistogamous flowers.

References: Arrington & Kubitzki (2003) In Kubitzki & Bayer (2003); Daoud & Wilbur (1965); Obae (2013); Sorrie (2015b) In Flora of North America Editorial Committee (2015); Wilbur & Daoud (1964). Show full citations.

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