Which plant is characterized by having leaves that are pointed, spiny, and submersed, with distinct arrangements at node points?

The choice of brittle naiad is appropriate because this aquatic plant is indeed characterized by its pointed, spiny leaves that are typically submersed in water. These leaves are arranged distinctly at the node points, which is a key identification feature. The structure of the leaves allows the plant to grow effectively in its aquatic environment, where it often forms dense stands.

In contrast, clasping-leaf pondweed features broader leaves that do not exhibit the same spiny characteristics and have a different arrangement. Eurasian watermilfoil is known for its finely dissected leaves that appear softer rather than spiny, and its growth habits differ as well. Southern naiad has a different leaf shape and arrangement, typically being less pointed and spiny than brittle naiad. Therefore, the identification for brittle naiad aligns not only with its physical characteristics but also with its ecological adaptations.