Low seed viability of a rare aster

 By Handley & Tronstad

 

Desert yellowhead (Yermo xanthocephalus)

Desert yellowhead (Yermo xanthocephalus) is a rare perennial plant, known from two populations in Wyoming, USA. The plant grows up to 30 cm tall with many bright yellow flowerheads that bloom during mid-summer in a sparsely vegetated, semi-arid ecosystem of big sagebrush (Artemisia tridentata), bunchgrass and cushion plants. Information about the reproductive ecology of desert yellowhead is sorely lacking. We measured the number and mass of seeds made by desert yellowhead plants when the only pollen available to flowers was from themselves (self-pollination). We also compared the seeds grown when pollinating insects transported pollen and when we supplied excess pollen from a distant plant (hand-pollinated). Additionally, we used vane traps and pan traps to capture pollinators, and we examined pollen carried by bees. The pollen of desert yellowhead was unique, and we could distinguish it from other aster species in the area. Although desert yellowhead can make seeds from its own pollen, pollen transported by pollinators increased the number of seeds capable of producing new plants. Only 12% of flowers produced seeds that had the potential to produce a new plant in the main population and none were able to do so in the second population, suggesting that something limited seed-set. Flowers that received pollen via insects and flowers that received excess pollen from hand-pollination made about the same number and mass of seeds, showing that pollinators were not responsible for the low number of quality seeds made. Nine types of bees carried pollen from desert yellowhead demonstrating that this plant is a valuable source of pollen and nectar for flower visitors. We recommend continued research to address what is limiting seed production to advance the knowledge and management of this declining plant species.

 

Read the scientific publication in JPE