Which type of weeds are described as having triangular stems and three rows of leaves?

Sedges are characterized by their triangular stems and the arrangement of their leaves in three distinct rows. This unique morphology sets sedges apart from other types of weeds. Unlike grasses, which typically have hollow, round stems, sedge stems are solid and triangular. Broadleaf weeds tend to have wider, flat leaves and do not exhibit the stem structure of sedges. Annual weeds refer to a lifecycle category and do not pertain specifically to the stem shape or leaf arrangement. Therefore, sedges are the correct answer as they specifically fit the description provided.