East Indian hygrophila is characterized by which of the following?

East Indian hygrophila is indeed characterized by squarish stems and oppositely arranged leaves. The plant belongs to the family Acanthaceae and typically exhibits a distinctive square stem, which is a trait seen in several members of this family. The arrangement of leaves is also an important identification feature, as they tend to grow in pairs opposite each other, which helps differentiate them from other aquatic plants.

The presence of a square stem is particularly significant for aquatic plants as it allows for easier navigation in flowing water environments and can contribute to the plant's overall structural integrity. In terms of leaf arrangement, the opposite placement allows for optimal light absorption and nutrient uptake, as the leaves can effectively capture sunlight without shading one another.

Other characteristics mentioned in the options, such as the leaves being firm and light green with a waxy exterior, the presence of dense hairy flowers, or heart-shaped leaves with ruffled flower petals, may describe other plants in different contexts but do not accurately reflect the specific morphological traits of East Indian hygrophila. Understanding these traits can aid in effective identification and management of aquatic weeds in Florida waterways.