Populations of large-flowered taxa of Carduus from many locations in the United States and Canada were grown in a common nursery from 1975 to 1983 at Lincoln, NE. Dates of first bloom and associated degree-day accumulation data exhibited some consistent relationships. Four species appeared to be represented in the collection. These included Carduus thoermeri Wein., C. macrocephalus Desf., and musk thistle (C. nutans L. ♯ CRUNU). A collection from British Columbia should be accorded species status but apparently has not been named in the literature. Interbreeding has taken place in the nursery and these combinations are intermediate between C. thoermeri and C. macrocephalus and between C. thoermeri and the British Columbia material. Some morphological characteristics supported these separations.

Occurrence of various growth stages of major pasture plants near Lincoln, NE, were recorded for 15 yr, 1958 to 1973. The phenology of 31 perennial and 16 biennial, winter annual, and annual broadleaf species and 18 grasses was determined. Phenological stages of broadleaf species were recorded as: emergence, stem elongation, first bud, first bloom, and seed firm. Events recorded for the grasses were: emergence, culm elongation, head exserted, anthesis, and seed firm. Much variation existed in phenology among and within life habit groupings of species. Year-to-year variability in phenology of these plants was dependent on temperature patterns of specific years. Studies of this nature are useful in developing more efficient control methods for weeds, insects, and diseases.