In which plant system are endodermal cells most prevalent?

Endodermal cells are primarily found in the root systems of plants. This specific type of cell forms a distinct layer in the root's interior, known as the endodermis. The endodermis serves as a critical barrier that regulates the flow of water and nutrients from the soil into the vascular system of the plant. It is equipped with a Casparian strip, a waxy band that helps control which substances can pass into the vascular tissues and ensures that the roots selectively absorb essential nutrients while preventing toxic substances from entering.

In contrast, other plant structures, such as leaves, stem nodes, and flower petals, do not contain significant quantities of endodermal cells. Leaves primarily consist of photosynthetic tissues, stems are mostly composed of vascular tissues and supportive structures, and flower petals are primarily made up of tissues involved in reproduction and attraction of pollinators. Thus, the prevalence of endodermal cells is a distinctive feature of root systems, making this the correct choice in the context of the question.