Reproductive strategy of Phacelia submutica (Boraginaceae; formerly in Hydrophyllaceae), a threatened plant species in western Colorado

Background/Question/Methods

Human activities including energy development, recreation, and livestock grazing in the Piceance Basin of western Colorado threaten many plant species endemic to the region.  One of these plants is Phacelia submutica (DeBeque phacelia), which was listed under the Endangered Species Act as a threatened species in 2011.  How this species will be affected by these activities, as well as how managers can mitigate the effects depends, in part, on its reproductive strategy.  This poster reports on experiments and observations conducted in 2011 at two populations to assess the species’ breeding system and identify insect pollinators.  Experimental treatments included 1) spontaneous autogamy (seed set when pollinators are excluded); 2) geitonogamy (within-plant pollination); 3) xenogamy (pollination between plants); and 4) an uncaged control to determine natural seed set.  We analyzed differences in the mean weight per seed and number of seeds per capsule (measures of pollination success and seed fitness) between treatments.  Pollinator observations were conducted through the species’ growing season (April and May) to identify pollinators and record their foraging activities.  Additionally, observations of reproductive development using a field microscope identified the timing of anthesis. 

Results/Conclusions

Phacelia submutica is a short-lived spring annual with a decumbent growth habit.  Tubular, cream colored flowers open in the morning and close by the second day after opening.  Anthesis occurs before or at the very beginning of bud opening and development is slightly protandrous (<20 minutes).  In 2011, plants produced a mean of 133 flowers per plant and production was highly variable (range of 1 to 451).  Fruits yielded on average 6 seeds and the mean natural weight of seeds was 0.39 ug per seed.  During pollinator observations, no insects were seen visiting flowers.  Statistical analyses of treated capsules found no difference in mean weight per seed within a capsule between the four treatments at either site.  However, preliminary assessment of seed production per capsule shows a higher mean number of seeds in geitonogamous and xenogamous treatments.  Observational data indicate that Phacelia submutica at these two populations are self-pollinating and do not require insect-mediated pollination for reproduction.  However, further studies are needed to determine whether 1) higher seed production per capsule in geitonogamous and xenogamous treatments is statistically relevant; and 2) this species is able to reproduce by apomixis (asexual reproduction).  The results of this research will be available to land managers to guide conservation and recovery strategies.