Invasive ornamental weeds, because they are so much more attractive than some of the other noxious weeds, are less likely to be seen as problematic plants. “But they are so pretty,” people cry. Perhaps, but these pretty plants are just as destructive to native ecosystems as their uglier friends
There are at least fifteen plants on the Colorado Department of Agriculture Noxious Weed list that can be considered attractive. Three of these weeds, myrtle spurge (Euphorbia myrsinites), cypress spurge (Euphorbia cyparissias), and orange hawkweed (Hieracium aurantiacum) are on “List A”. This means that they have relatively small populations and must be eradicated everywhere in Colorado, including municipalities.
The remainder are “List B” weeds, which have a different designation in each county. Some of the worst offenders on this list include tamarisk (Tamarix ramosissima) and Russian olive (Eleagnus angustifolia), trees which take over the banks of streams and rivers, depleting water courses and out competing native riparian species. Perhaps the three most problematic herbaceous plants are oxeye daisy (Chrysanthemum leucanthemum), and yellow and Dalmation toadflaxes (Linaria vulgaris, and L. genistifolia). All of these naturalize readily, crowd out native plants, and are unpalatable to livestock.