A grass is a member of the Poaceae family, also known as Gramineae, which is the largest family of flowering plants. Grasses are characterized by their jointed stems, narrow leaves with parallel veins, and small, inconspicuous flowers. They are also typically wind-pollinated and self-fertilizing.

Traditionally, grasses have been classified as being either true grasses or sedges. True grasses have round stems and their leaf blades are not fused together at the base. Sedges have triangular stems and their leaf blades are fused together at the base.

However, a recent study based on chloroplast DNA analysis has challenged the traditional classification of grasses. The study found that true grasses and sedges are not actually closely related. In fact, sedges are more closely related to rushes than they are to true grasses.

This new classification system has not yet been widely accepted, but it has some important implications. For example, it means that the term "grass" may not be as well-defined as we thought. It is possible that some plants that we currently consider to be grasses may actually be sedges, and vice versa.

The study also has implications for our understanding of the evolution of grasses. Traditionally, it was thought that true grasses evolved from sedges. However, the new classification system suggests that sedges and true grasses may have evolved from a common ancestor.