Barneby’s clover (Trifolium barnebyi) is a Wyoming endemic plant, known from the southeastern foothills of the Wind River Range and southern Beaver Rim in Fremont County. Barneby’s clover is considered a Sensitive Species by the Wyoming Bureau of Land Management. Rare plants often have specialized pollinators and the abundance of these pollinators can determine their reproductive success. Therefore, the mutualisms between rare plants and pollinators are vital. During the 2019 field season, we investigated the degree to which Barneby’s clover was pollen-limited by recording the number, mass and viability of seeds produced in hand-pollinated (pollen not limited), open (insect pollinated) and bagged (pollen excluded) blooms in three areas. Bagged flowers restrict insects from pollinating and measured the degree to which Barneby’s clover can self-pollinate. We used Tetrazolium staining to estimate the viability of seeds produced in all treatments. Seed number, mass and viability were analyzed using generalized linear models in Program R. Comparing the number, mass and viability of seeds produced by flowers in open vs. hand pollinated blooms allowed us to evaluate the degree to which Barneby’s clover is pollen-limited.
Results/Conclusions
The number of ovules remained constant across treatments and populations (1-4 ovules per pod; average of 2 ovules per pod), and may be constrained by genetics. However, no viable seeds were produced in the bagged treatment plants, indicating no self-fertilization. Although a few of the ovules in the bagged treatment started to develop, they were hollow and none were viable. The open and hand-pollinated treatments did not differ in the number or mass of viable seeds, suggesting that insects were not limiting seed production. The mass and number of viable seeds per flower increased with Julian day pollinated, as plants in the south and east sites bloomed later than the north site. Pollinator abundance likely affected seed set. The number of bees captured in traps increased through the blooming period. More bees likely corresponded with increased mass and viability of seeds produced. Fertility also appeared to vary among individual plants. Environmental factors (e.g., soil, wind, rain, temperatures) may limit the mass and viability of seeds produced at different sites, which may be due to differences in topography, exposures, and geology. Understanding what limits seed production will help manage the perpetuation of this rare plant.