The following structures are found on the underside of fern leaves and contain sporangia:

sori

rhizomes

megaphylls

microphylls

The sori are found on the underside of fern leaves and contain sporangia.

Explanation:

Sori are structures on the underside of leaves of ferns. They consist of a variety of sporangia and sometimes a indusium that protects the young sporangias. The shape of the sorus is often of importance when determining a species of fern.