Ambrosia tomentosa
(Skeletonleaf Burr Ragweed or Skeletonleaf Bursage)
Family:
Asteraceae (Sunflower)
  
Skeletonleaf Bursage grows along roadsides and on sandy sites on the plains. The plant has deeply dissected leaves, giving it a "skeleton" appearance. Male flowers hang in umbels from the top portion of the stem. Female flower heads are spiny burr-like structures in the leaf axils with two carpels. The finely dissected leaves and spiny female flowers help to separate A. tomentosa from other Ambrosia spp. Ragweed pollen causes hay fever.

Compare to Ambrosia psilostachya, which has less dissected leaves.
Female flowers of A. psilostachya lack spines.

Compare to Ambrosia trifida, which is a taller plant with broader leaves. Female flowers of A. trifida lack spines. A. trifida has a black rib on the involucre of the male flower umbels.

Vegetation zone:  Plains
Time of bloom:  July - October
Origin:  Native
Eastern Colorado Wildflowers