Dahlia Cav.
Herbaceous perennials often woody toward base, or scrambling epiphytes. Lvs opposite or whorled, simple and entire or lobed, to 1-3-pinnate. Capitula pedunculate, solitary. Involucral bracts in 2 rows; outer row foliaceous; inner row membranous. Receptacle flat or nearly so; scales present. Outer florets ♀ or sterile, ligulate, white, pale lavender to deep purple, or yellow to orange to deep scarlet. Inner florets ⚥, tubular (or replaced by ligulate florets in many cvs). Achenes all similar, linear-oblong or spathulate, compressed but not winged, often constricted below a disc at apex; pappus usually 0, sometimes of 2 rudimentary awns.
Key
26 spp., Mexico, C. and northern S. America, with most spp. in mountains of Mexico. Naturalised sp. 1 and 1 cultivated hybrid.
In spite of their long history in cultivation, the relationships of cultivated dahlias to their wild progenitors is relatively well understood. The genus has been revised by Sorensen, P. D., Rhodora 71 : 309-416 (1969).
