"Sori" redirects here. For the commune in Italy, see Sori, Italy; for the villages in Azerbaijan see Soru and Sors, Azerbaijan.

In ferns, a sorus (pl. sori) is a yellowish or brownish cluster of sporangia on the edge or underside of a fertile frond. In some species, they are protected during development by a scale or film of tissue called the indusium, which forms an umbrella-like cover.

Sori occur on the sporophyte generation, the sporangia within producing haploid meiospores. As the sporongia mature, the indusium shrivels so that spore release is unimpeded. The sporangia then burst and release the spores.

The shape, arrangement, and location of the sori are often valuable clues in the identification of fern taxa. Sori may be circular or linear. They may be arranged in rows, either parallel or oblique to the costa, or randomly. Their location may be marginal or set away from the margin on the frond lamina. The presence or absence of indusium is also used to identify fern taxa.

In fungi and lichens, a sorus is a cluster of sporangia surrounded by an external layer.

Gallery

References and external links

• DiversityOfLife – Fern identification tool.
• Encyclopædia Britannica: sorus 2007. Encyclopædia Britannica Online. Retrieved 20 November 2007.