I visited my parents in Iowa last week. One thing I did was help with pulling out thistles that had been spreading throughout a couple garden beds — 89 plants one day, a couple more another day.
But what kind of thistle were they? I was hoping non-native since my hope is to nudge things in the direction of native plants.
Per a user on iNaturalist, they seem to be Creeping Thistle (Cirsium arvense). Wikipedia says: “Cirsium arvense is a perennial species of flowering plant in the family Asteraceae, native throughout Europe and western Asia, northern Africa and widely introduced elsewhere… Creeping thistle is a herbaceous perennial plant growing up to 150 cm, forming extensive clonal colonies from thickened roots that send up numerous erect shoots during the growing season… Given its adaptive nature, Cirsium arvense is one of the worst invasive weeds worldwide… differs from other native North American species in having large roots and multiple small flower heads on a branched stem.”
From the Wikipedia entry for a different plant, we learn the meaning for “arvense”: “The specific epithet arvense is from the Latin ‘arvum’, meaning ‘ploughed’, referencing the growth of the plant in arable soil or disturbed areas”.
There are 493 species in the genus Cirsium, the plumed thistles. Xerxes mentions 6 thistles native to Iowa. EasyScape identifies only one of these as being native in the Ames, Iowa, area though: Field Thistle (Cirsium discolor).
Creeping Thistle (Cirsium arvense) is a host plant for painted ladies: “The few species that do interact or harm the thistle include: Orellia ruficauda (a seed head predator), Ceutorhychus litura (a stem-mining weevil) and Vanessa Cardui (larval leaf-feeding Painted Lady Butterfly).”
Hopefully the overall ecological impact from removing them was positive though?
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