Last Addition: April 4, 2002
Each "thumbnail" image below is linked to a larger photograph.
Calycadenia pauciflora formerly included small-headed, white-flowered populations on both sides of the Central Valley of California. Biosystematic studies began in 1970 led to circumscription of the populations in the Sierra foothills south of Sacramento as a distinctive new species, C. hooveri, with n = 7 chromosomes. The remaining North Coast Range populations of C. pauciflora were further characterized as a complex of chromosome races, four with n = 6 chromosomes (Elegans, Healdsburg, Ramulosa, and Tehama) and one with n = 5 chromosomes (Pauciflora). The races are differentiated by dysploidy, reciprocal chromosome translocations, and at least one pericentric inversion. Races Elegans and Healdsburg are presently considered to belong to C. fremontii (Jepson Manual, 1993). Recently, a small-headed chromosome race with n = 6 chromosomes (Wurlitzer) from the north end of the Central Valley NW of Chico was discovered. It was initially thought to represent a second population of the recently rediscovered C. fremontii but morphologically it aligns more closely with C. pauciflora. The species is found at elevations from about 70-1000 m. Interspecific hybridization between C. pauciflora (races Ramulosa and Tehama) and C. fremontii (races Dry Creek and Elegans) occurs in nature. Especially notable is natural hybridization between Race Elegans (C. fremontii) and Race Pauciflora (C. pauciflora) at sites of sympatry at the ecotone between valley grassland and chaparral (e.g. near the Napa-Lake County line along Morgan Valley Road - photo below). All possible combinations of inter-racial hybrids have been produced artificially. Additional interspecific hybrids between C. pauciflora and C. fremontii, C. hooveri, C. multiglandulosa, C. oppositifolia, and C. spicata have been produced experimentally.
|Race Pauciflora. 1 - Habitat in Napa County. 2 - Greenhouse-grown progeny of fruit from Napa County population. 3 - Closer view of flowering heads, note fewer florets in this and the following races compared to Healdsburg and Elegans above. The peduncular bracts commonly have 1-5 tack-shaped glands in most populations of C. pauciflora. 4 - Face view of single head. 5 - Ray and disk florets.|
|Race Ramulosa. 1 - Greenhouse-grown progeny from Lake County population, 2 - Flowering head, note similarity with other small-headed races.|
|Race Tehama. 1 - Greenhouse-grown progeny from Tehama County population, 2 - Flowering head, note similarity with other small-headed races.|
|Race Wurlitzer. 1, 2 - Butte County habitat, 3 - Greenhouse-grown progeny, 4 - close view of flowering heads, note general similarity with other small-headed races.|
|Zone of sympatry between C. fremontii, Race Elegans (chaparral) and C. pauciflora, Race Pauciflora (grassland) near the Napa-Lake County line along Morgan Valley Road. Hybrids are established in a very narrow strip at the interface of the two races.|
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