Linaria vulgaris (yellow toadflax) and Linaria purpurea (purple toadflax)
As I was saying the other day, a disproportionate number of the world's wildflowers are either yellow or purple and nothing demonstrates this better than these two European 'invasive weeds'; yellow and purple toadflax. No one knows when these plants first arrived in North America but I would guess that they probably showed up sometime in the first five years of European colonization - on a pair of muddy boots.
Yellow toadflax is mildly toxic to livestock but purple toadflax is very poisonous. Probably because our European cattle, sheep and goats coevolved with purple toadflax, they generally avoid eating it. Still farmers don't like the way purple toadflax takes over their fields and it's regarded as a serious agricultural pest.
Recent studies of botanical diversity show only plants that people like are prospering in the Anthropocene. Native plants are becoming extinct in unprecedented numbers and being outcompeted by non-native, invasive weeds is part of the problem. But somewhere in my rebel heart, I admire weeds. Weeds grow wherever they want, they don't seek our approval and they don't care what we think of them. No doubt, long after we're gone, it will be the 'weeds' that will inherit the Earth.