What is "sorus"

Sorus \So"rus\, n.; pl. Sori. [NL., fr. Gr. ? a heap.]

1. (Bot.) One of the fruit dots, or small clusters of sporangia, on the back of the fronds of ferns.

2. 1. In parasitic fungi, any mass of spores bursting through the epidermis of a host plant.

   2. In lichens, a heap of soredia on the thallus.

n. 1 (context mycology lichenology English) Any reproductive structure, in some lichens and fungus, that produces spores. 2 (context botany English) A cluster of sporangium on the edge or underside of a fern frond.

1. n. a spore-producing structure in certain lichens and fungi

2. cluster of sporangia usually on underside of a fern frond

3. [also: sori (pl)]

A sorus (pl. sori) is a cluster of sporangia (structures producing and containing spores) in ferns and fungi. This New Latin word is from Ancient Greek σωρός (sōrós ‘stack, pile, heap’).

In fungi and lichens, the sorus is surrounded by an external layer. In some red algae it may take the form of a depression into the thallus.

In ferns, these form a yellowish or brownish mass 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 meio spores. 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.