Which weed category is characterized by having one seed leaf and parallel leaf veins?

The characteristics of having one seed leaf, or cotyledon, and parallel leaf veins are distinctive features of monocotyledonous plants, commonly known as grasses. Grasses exhibit these traits, which set them apart from other categories of weeds. The parallel venation in the leaves is a typical hallmark of monocots, providing an additional indicator that confirms their classification.

In contrast, broadleaf plants are dicots, which usually have two seed leaves and a network of branching veins. Sedges, while also monocots, have different leaf structures and growth habits compared to typical grasses. Annuals refer to a lifecycle classification, indicating that they complete their life cycle in one year, and can include both grasses and broadleaf plants. Therefore, the defining features of grasses clearly align with the description of having one seed leaf and parallel leaf veins.