Calycadenia truncata DC.

Last Addition: February 27, 2007.

Each "thumbnail" image below is linked to a larger photograph.

Calycadenia truncata is easily the most widespread species in the genus, extending from mountainous southern Oregon south along the Sierran foothills and Coast Ranges and out onto the floor of the Central Valley.  Populations can be found at elevations ranging from about 50 to 1500 meters. The flower color is always yellow, sometimes with reddish eyespots on the ray corollas. The peduncular bracts have one terminal tack-shaped gland.  The plant surfaces are commonly glaucous and the ray achenes rugose.  Plants are generally robust, with large, showy heads.  The chromosome number of C. truncata is n = 7.   Preliminary studies indicate that the species includes three or more chromosome races differentiated by reciprocal translocations.  Calycadenia truncata is very closely related and morphologically similar to the diminutive, self-compatible species, C. micrantha.  Putative natural interspecific hybrids with C. multiglandulosa have been observed east of Sacramento.   Artificial interspecific hybrids have been produced with C. mollis, C. villosa, and Osmadenia tenella.  Calycadenia  micrantha readily hybridizes with C. truncata in vitro but viable hybrid fruits are formed only on C. micrantha parents.

1 - Shasta County habitat, 2 - San Joaquin County population, 3 - Shasta County populaiton, 4 - Greenhouse-grown progeny from Santa Clara County, 5-6 - Close-up of flowering heads of San Joaquin County plants, note black tar-like exudate of tack-shaped glands, 7 - Flowering head of plant from El Dorado County, 8 - Close-up of flowering head in bud showing details of peduncular bracts and tack-shaped glands, note insect trapped in droplet of exudate.

Comparison of heads of Calycadenia truncata (left) and the self-compatible derived species C. micrantha (right).

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