Herbs, perennial, or subshrubs, 0.4–8 dm. Stems not dimorphic, hairy, usually some hairs (chasmogamous), 1–20 per capsule (cleistogamous). x = 10.
North America, Mexico, West Indies (Dominican Republic), Central America, South America.
Species 21 (15 in the flora).
Crocanthemum was created in 1836 to accommodate the New World species of Helianthemum, but most authors have not recognized the distinction. Studies by J. Arrington (2004) and B. Guzmán and P. Vargas (2009) showed that traditional Helianthemum is not monophyletic. Helianthemum is now a genus of some 80 species restricted to the Old World, and Crocanthemum is a New World genus most closely related to Hudsonia. Differences in leaf arrangement, pollen type, style architecture, and funicle and embryo shape all serve to distinguish the two genera. In particular, the style base in New World species is broad (broader than the apex) and confluent with the outline of the ovary, whereas in Old World species the style is tapered from apex to the narrower base. The style in New World species is short and straight, but long and curved in Old World species. In New World species, leaves are alternate and estipulate; in Old World species leaves are mostly opposite and stipulate. Regarding the apparent close relationship between Crocanthemum and Hudsonia, Guzmán and Vargas noted that these two genera have unique pollen types, and that both differ from Old World Helianthemum. More complete sampling of New World taxa may be necessary to resolve the issue of whether Crocanthemum is distinct from Hudsonia.
A prominent feature of Crocanthemum is production of dimorphic flowers in all but the Californian species. Showy, chasmogamous flowers are produced early in the growing season, followed one to three months later by apetalous, cleistogamous flowers (simultaneous in C. georgianum and C. glomeratum). Flowering dates cited are for chasmogamous flowers.
All species of Crocanthemum are fire-tolerant, readily resprouting from the woody caudex.
|1||Capsules (chasmogamous flowers) stellate-pubescent distally||> 2|
|1||Capsules (chasmogamous flowers) glabrous||> 3|
|2||Chasmogamous capsules 3-valved; inflorescences umbellate; stems 5–15(–20) cm.||Crocanthemum arenicola|
|2||Chasmogamous capsules 2-valved; inflorescences thyrsiform; stems 20–35(–41) cm.||Crocanthemum nashii|
|3||Leaf blades with lateral veins obscure abaxially||> 4|
|3||Leaf blades with lateral veins raised abaxially||> 9|
|4||Cleistogamous flowers 2–10 per glomerule; w Texas eastward||> 5|
|4||Cleistogamous flowers 0; California||> 6|
|5||Subshrubs; petioles 0–2 mm; leaf margins nonrevolute; inner sepals of cleistogamous flowers 2.4–5 mm.||Crocanthemum glomeratum|
|5||Herbs; petioles 1–4 mm; leaf margins revolute; inner sepals of cleistogamous flowers 1.5–1.8 mm.||Crocanthemum rosmarinifolium|
|6||Pedicels stellate-pubescent and densely glandular-hairy; outer sepals lanceolate; calyx hairs 1–1.7 mm, simple, strigose (sometimes also short-stellate-hairy).||Crocanthemum greenei|
|6||Pedicels with sparse or no glandular hairs; outer sepals linear; calyx hairs to 1 mm, stellate-pubescent||> 7|
|7||Petals 3–6 mm; stems 10–45 cm, spreading to erect-fastigiate; capsules 2.8–3.8 mm.||Crocanthemum scoparium|
|7||Petals 6–12 mm; stems 30–80 cm, erect; capsules 3.5–4.3 mm||> 8|
|8||Stems glabrate to sparsely stellate-pubescent; leaves and inflorescences stellate-pannose; inflorescences broad, with spreading branches.||Crocanthemum aldersonii|
|8||Stems, leaves, and inflorescences usually stellate-pannose, (sometimes sparsely stellate-pubescent); inflorescences narrow.||Crocanthemum suffrutescens|
|9||Basal leaves rosette- or mat-forming||> 10|
|10||Basal leaf blades spatulate to obovate or elliptic, 5–18(–28) mm wide, sparsely stellate-pubescent adaxially; cleistogamous flowers rarely produced.||Crocanthemum carolinianum|
|10||Basal leaf blades spatulate to oblanceolate, 5–11 mm wide, stellate-pannose adaxially; cleistogamous flowers 2–7 per cyme.||Crocanthemum georgianum|
|11||Cleistogamous flowers in terminal corymbiform cyme.||Crocanthemum corymbosum|
|11||Cleistogamous flowers in glomerules on lateral branches or terminal glomerules (C. glomeratum) or racemose cymes (C. georgianum)||> 13|
|12||Cauline leaf blades stellate-tomentose or stellate-pubescent, without simple hairs; chasmogamous flowers (1–)2–18; stems not red-tinged||> 14|
|13||Stems ascending to erect; adaxial leaf surface ± lustrous under hairs; cleistogamous flowers with outer sepals 0.2–0.5 mm.||Crocanthemum canadense|
|13||Stems ascending to divergent; adaxial leaf surface dull under hairs; cleistogamous flowers with outer sepals 0.4–1 mm.||Crocanthemum dumosum|
|14||Subshrubs; petioles 0–2 mm.||Crocanthemum glomeratum|
|14||Herbs (or subshrubs in C. georgianum); petioles 1–5 mm||> 15|
|15||Chasmogamous and cleistogamous flowers produced together on same inflorescence; basal leaves present or absent.||Crocanthemum georgianum|
|16||Stems (12–)20–50(–67) cm, clustered on vertical caudex; outer sepals of cleistogamous flowers linear, 0.5–1.5 mm.||Crocanthemum bicknellii|
|16||Stems 10–27(–35) cm, scattered on horizontal rootstock; outer sepals of cleistogamous flowers rudimentary, 0.2–0.5 mm.||Crocanthemum propinquum|