Securigera varia or Coronilla varia (Crownvetch)
Family: Fabaceae (Pea)
  
At first glance, Crownvetch might appear to be an Astragalus sp.. Close examination, however, reveals that the flowers are arranged in an umbel, radiating from a single central point. Sepals are glabrous (hairless), while most Astragalus sp. have hairy sepals. Leaflets often have a pointed tip. The keel (inner petals of the flower) has a purple tip.

Vegetation zone:  Plains
Time of bloom:  April - September
Origin:  Introduced
Eastern Colorado Wildflowers