Which of the following examples is considered a noxious weed?

Thistle is classified as a noxious weed due to its invasive growth patterns and the difficulties it poses to agricultural practices and natural ecosystems. Noxious weeds are typically aggressive plants that can outcompete native vegetation, interfere with crop production, and contribute to biodiversity loss. Thistle species, such as Canada thistle, are particularly problematic because they reproduce quickly and can spread rapidly through both seeds and root systems. As a result, they can dominate fields and gardens, negatively impacting local flora and agricultural productivity.

In contrast, the other options listed do not share the same classification as a noxious weed. Maple trees and clover, for example, are commonly found in landscapes and often provide ecological benefits, whereas dandelions, while sometimes considered a nuisance in lawns, are not classified as noxious weeds due to their relatively harmless presence and potential benefits, such as serving as a food source for pollinators. Therefore, thistle stands out as a significant concern in weed management due to its detrimental effects on agriculture and natural ecosystems.