Final answer:
The eusporangiate fern that produces sporangium laterally is the Whisk fern (Psilotum), which contains sporangia on small yellow knobs formed on their green stems. Unlike many ferns with sori under their fronds, whisk ferns have lateral sporangia due to the absence of typical fern foliage.
Step-by-step explanation:
The type of eusporangiate fern that produces sporangium laterally is the Whisk fern (Psilotum). Whisk ferns are part of the class Psilotopsida, which is known for lacking both roots and leaves due to evolutionary reduction. Instead, photosynthesis takes place in their green stems that branch dichotomously. It is on their green stems that small yellow knobs form either at the tip of a branch or at branch nodes, and these knobs contain the sporangia which are developed laterally.
In contrast to whisk ferns, most ferns produce sporangia on the underside of their fronds in clusters known as sori. Their spores are released into the air from the sporangium and upon landing on a suitable substrate, germinate to form a gametophyte. Whisk ferns, despite their appearance, are closely related to true ferns and follow a similar life cycle but with structural variations due to their evolutionary path.