Which term refers to the below ground, horizontal stems that can reproduce asexually?

The term that refers to below-ground, horizontal stems capable of asexual reproduction is "rhizome." Rhizomes are specialized storage stems that grow horizontally beneath the soil surface. They not only serve as a means of vegetative reproduction, allowing new plants to sprout at nodes along the rhizome, but they also store nutrients, which can help the plant survive adverse conditions.

In contrast, stolons, which are above-ground horizontal stems, also facilitate asexual reproduction but do so by producing new plants at their tip or at nodes above the ground. Culm refers specifically to the stem of grass and does not imply any mode of asexual reproduction. Internode denotes the segment of a stem between two nodes and is not type-specific for reproduction. Understanding these differences helps clarify why rhizomes are the correct choice for this question.