Spring flowers are finally filling the fields. Milk vetch, penstemons, wild onions and marsh marigolds all caught my eye as I hiked though the towering cottonwoods along Fountain Creek, at the base of the Rockies here in central Colorado. I was particularly impressed by huge swaths of a foamy white flower I didn’t immediately recognize.

Counting the petals—each tiny flower had four—and examining the foliage led us to conclude the plants were Crucifers, members of the mustard family. Sure enough, we were enjoying the pretty flower heads of Whitetop (Cardaria draba), an aggressive import from Europe and Asia that is listed as a noxious weed here in Colorado (List B). Oh dear.

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