Breeding biology and bee guild of douglas' dustymaiden, chaenactis douglasii (Asteraceae, Helenieae)

摘要

Douglas' dustymaiden, Chaenactis douglasii (Hook.) Hook. & Arn., is a widespread, inconspicuous, short-lived perennial wildflower that blooms in early summer and is found in basin sagesteppe to upper montane areas throughout the U.S. Intermountain West. The species is proving practical to grow for seed and is expected to be used for western rangeland rehabilitation. Through manual pollination experiments, C. douglasii was found to be only weakly self-fertile; 15% of flowers from geitonogamy and autogamy treatments yielded filled achenes. In contrast, 57% of outcrossed flowers produced achenes filled with endosperm, with every capitulum yielding some fertile seeds. Freely visited flowers from a wild population produced 91% fertile achenes, indicating that seed production was not pollinator limited. Floral visitors to C. douglasii were sparse, consisting entirely of bees, most of them floral generalists. Museum specimens of bees taken at C. douglasii and 3 closely related congenerics comprise 175 species in 39 genera and all 6 North American bee families. A population of the manageable mesolectic cavity-nesting bee, Osmia californica, when released at one sagesteppe site, provisioned its cells primarily with pale, spiny pollen resembling that of the C. douglasii growing at the site. This bee and the honey bee appear most promising for pollinating dustymaiden that is being farmed for seed.