sorus

A sorus is a cluster of sporangia on the fronds of a fern, functioning as the reproductive unit that produces spores. The sporangia within a sorus undergo meiosis to generate haploid spores, which are released to disperse and potentially form new gametophytes.

Most sori are located on the underside of the leaf, often near the veins. They vary in shape, being circular or reniform (kidney-shaped) in many species, or elongated in others. The arrangement of sori on the frond can be marginal along the leaf edge, scattered along the underside, or organized in regular rows or patches. In many ferns, the position and pattern of sori are distinctive and used for taxonomic identification.

Protection of the sorus is often provided by a specialized tissue called an indusium. Indusia come in several forms, including umbrella-like or cup-shaped coverings, as well as false indusia formed by the curling of the leaf margin over the sorus. The presence, absence, and type of indusium are important diagnostic features in fern morphology.

Life cycle and dispersal: When mature, the sporangia release spores, typically through a mechanism involving an annulus that helps eject the spores. The released spores germinate to form a free-living gametophyte (prothallus), which produces sexual organs. Fertilization then gives rise to a new diploid sporophyte, completing the fern’s life cycle.

Note: The term sorus is singular; the plural is sori. Sori are a key feature in fern anatomy and a primary source of information for identifying fern species.