Milk thistle (Silybum marianum) can be a pain if it's growing in your yard. It's non-native and can be an invasive plant, as Keri Wilson, horticulturist and writer for Garden Media Group ...

They spread via seeds and stray plant parts. Since musk thistle (Carduus nutans) can produce over 20,000 straw-colored seeds singularly, it quickly carpets the area, outcompeting native vegetation.