Milkweed and Sow thistle

Milkweed noun - Annual Eurasian sow thistle with soft spiny leaves and rayed yellow flower heads.

Sow thistle and milkweed are semantically related. In some cases you can use "Sow thistle" instead a noun "Milkweed".

Sow thistle noun - Any of several Old World coarse prickly-leaved shrubs and subshrubs having milky juice and yellow flowers; widely naturalized; often noxious weeds in cultivated soil.

Milkweed and sow thistle are semantically related. Sometimes you can replace term "Milkweed" with "Sow thistle", this terms are similar.