The underside of a fertile frond of Dicksonia antarctica. Each dot is an individual sorus.

In ferns, a sorus (pl. sori) is a cluster of sporangia on the edge or underside of a fertile frond. In many species, they are protected by an umbrella-like cover called the indusium. Image File history File links Download high resolution version (1186x1533, 415 KB) Species Dicksonia antarctica Genus Dicksonia Familia Dicksoniaceae Picture taken by DanielCD on 17 May 2005. ... Image File history File links Download high resolution version (1186x1533, 415 KB) Species Dicksonia antarctica Genus Dicksonia Familia Dicksoniaceae Picture taken by DanielCD on 17 May 2005. ... Binomial name Dicksonia antarctica Tasmanian Tree Fern (Dicksonia antarctica) is an evergreen tree fern native to parts of Australia, namely New South Wales, Tasmania, and Victoria. ... Classes Marattiopsida Osmundopsida Gleicheniopsida Pteridopsida A fern, or pteridophyte, is any one of a group of some twenty thousand species of plants classified in the Division Pteridophyta, formerly known as Filicophyta. ... A sporangium (pl. ... A fern with simple (lobed or pinnatifid) blades, the dissection of each blade not quite reaching to the rachis. ...

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. A sporophyte is the diploid structure or phase of life of a sexually reproducing plant. ... Haploid (meaning simple in Greek) cells have only one copy of each chromosome. ... The term spore has several different meanings in biology. ...

The shape of the sori is often a valuable clue in the identification of fern taxa. Sori may be circular or linear, and marginal or set away from the margin on the frond lamina.