Key to Figures
Photo 1 shows the long, yellow/green bristles on the involucral bracts of Crepis barbigera s.s. and a bee visiting a flower head in full bloom. Of course, the visiting bee is of little concern to the plant given that its seeds are clonal and don't require fertilization. The picture was taken on June 6th, 2007. This population is located south of Chelan (47.806000, -120.136000), Chelan County, Washington. Octoploid (8n) Crepis barbigera s.s. were found only on south facing slopes while diploid Crepis atribarba occurred only on north facing slopes at this site.
Photo 2 is of another Crepis barbigera s.s. and was taken on June 21st, 2007. This individual has the largest genome reported in the sunflower family. The population is located at the Tom McCall Preserve, west of Rowena, Wasco County, Oregon (45.668600, -121.304000). The mountain in the background is Mount Hood.
Figure 3 is a distribution map of Crepis barbigera s.s. and closely related Crepis atribarba.
We continue today with the University of British Columbia's Celebrate Research Week series, as organized by Claire. Claire introduces today's UBC researcher:
Chris Sears is currently working on his Ph.D. in Dr. Jeannette Whitton's lab for systematics, taxonomy and population genetics of the North America Crepis agamic complex and is working on reclassification of certain Crepis species. Chris Sears has been a T.A. of mine for two of my botany classes here at UBC (one of them being seed plant taxonomy) and I'm excited to have him share his taxonomic work with us for research week. Thank you Chris!
Crepis is a genus of ca. 200 species in the Cichoriodideae subfamily of Asteraceae. As such, like dandelions, they have yellow ligulate flowers and exude white milky latex when injured. There are ten species of Crepis native to North America. Two other North American species traditionally placed in Crepis, Crepis nana and Crepis elegans, have been transferred to the genus Askellia based on morphological and DNA sequence data.
Crepis barbigera is a member of the North American Crepis agamic complex. An agamic complex comprises sexual diploids (2n) and closely related apomictic polyploidy (3n,4n, etc) derivatives. Apomixis is the production of seeds which are clones of the mother plant. This western North American group is well known amongst plant evolutionary biologist because one of the fathers of the modern evolutionary synthesis, Ledyard Stebbins, co-authored a monograph of the group with E.B Babcock entitled American species of Crepis. Published in 1938 this was one of the first monographical works of the biosystematics era. It established the North American Crepis agamic complex as an early plant model system for the taxonomic treatment of agamic complexes, and gave critical insight into evolutionary processes of such groups.
Babcock and Stebbins recognized nine species in the North American Crepis agamic complex. Seven of the nine species consist of diploid and polyploid individuals while the remaining two consist of only polyploid individuals. For example, Crepis atribarba and Crepis acuminata are made up of diploid and polyploid individuals but Crepis barbigera consists only of polyploids. In Dr. Jeannette Whitton's lab at the University of British Columbia, I am in the process of updating the taxonomy of the North American Crepis agamic complex to reflect new data gleaned from ploidy analysis, morphology, distribution, ecology, and DNA sequence data. As circumscribed by Babcock and Stebbins, DNA sequence data indicates that most individuals of Crepis barbigera are closely related to Crepis atribarba but a few are more closely related to Crepis acuminata. Those individuals that are closely related to Crepis atribarba have the largest known genome in Asteraceae. They are also morphologically similar to the nomenclatural type of Crepis barbigera, but also share qualitative morphological characters with Crepis atribarba. These individuals will be called Crepis barbigera sensu stricto (s.s., or in the strictest sense) below. Those plants that are closely related to Crepis acuminata share qualitative morphological characters with that species, and have much smaller genomes compared to Crepis barbigera s.s.
Whitton and I are currently preparing a paper to be submitted to a scientific journal that will recommend reducing Crepis barbigera s.s. to a subspecies of Crepis atribarba, and expanding the circumscription of Crepis acuminata to include those individuals formally placed in Crepis barbigera that are closely related to Crepis acuminata. This recircumscribed Crepis barbigera s.s. can be recognized by conspicuous, yellow/green, long, curved bristles on the involucral bracts of the flower heads. Crepis atribarba sometimes has bristles on their involucral bracts but they are not as long and are usually black and straight. Crepis barbigera s.s. is narrowly distributed from central Washington to the Columbia River Gorge, and extends eastward into northern Idaho (see map). Like other members of the North American Crepis agamic complex it can be found on the sagebrush steppes and in the lower margins of ponderosa pine forests. Based on historic records it is apparent that the distribution of this taxon has been reduced because much of the Columbia Plateau has been converted to agriculture.