Which plant family includes thistles and knapweeds?

The plant family that includes thistles and knapweeds is indeed the Asteraceae family. This family, also known as the daisy or composite family, is characterized by its flower heads, which often contain both ray and disc florets, giving them a distinctive appearance. Thistles and knapweeds, which are well-known as invasive weeds, belong to this family and share similar floral structures and ecological behaviors.

Asteraceae is one of the largest plant families and includes a wide variety of plants, making it significant for both ecological and agricultural purposes. Members of this family can be found in various habitats and can have both beneficial (e.g., as pollinator plants) and detrimental (e.g., as weeds) impacts on ecosystems.

The other plant families listed, such as Caryophyllaceae, Chenopodiaceae, and Convolulaceae, contain very different types of plants that do not include thistles and knapweeds, highlighting the specific nature of the Asteraceae family in this context.