Which species has leaves that are spiny, oblong or lance-shaped?

• A. Canada Thistle
• B. Plumeless Thistle
• C. Diffuse Knapweed
• D. Spotted Knapweed

Answer: (A)

Leaves that are spiny and oblong or lance-shaped point to a thistle with stiff, spear-like foliage. Canada thistle fits this description well because its leaves are elongated, taper to a point, and have sharp spines along the edges, giving them a distinctly prickly feel. The other plants listed have leaves that differ in texture and form: knapweeds typically have softer, non-spiny leaves that are often lobed or pinnate, and while plumeless thistle is also a thistle, its leaves tend to be more deeply divided rather than simply oblong or lance-shaped. So the leaf shape and the presence of spines make Canada thistle the best match.