In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many plants, algae, fungi and some protozoans. A chief difference between spores and seeds as dispersal units is that spores have very little stored food resources compared with seeds.

Spores are usually haploid and unicellular and are produced by meiosis in the sporophyte. Once conditions are favorable, the spore can develop into a new organism using mitotic division, producing a multicellular gametophyte, which eventually goes on to produce gametes.

Two gametes fuse to create a new sporophyte. This cycle is known as alternation of generations, but a better term is "biological life cycle", as there may be more than one phase and so it cannot be a direct alternation. Haploid spores produced by mitosis (known as mitospores) are used by many fungi for asexual reproduction.

Spores are the units of asexual reproduction, because a single spore develops into a new organism. By contrast, gametes are the units of sexual reproduction, as two gametes need to fuse to create a new organism.

The term spore may also refer to the dormant stage of some bacteria or archaea; however these are more correctly known as endospores and are not truly spores in the sense discussed in this article. The term can also be loosely applied to some animal resting stages. Fungi that produce spores are known as sporogenous, and those that do not are asporogenous.

The term derives from the ancient Greek word σπορα ("spora"), meaning a seed.

Classification

Spores can be classified in several ways:

By spore-producing structure

In fungi and fungus-like organisms, spores are often classified by the structure in which meiosis and spore production occurs. Since fungi are often classified according to their spore-producing structures, these spores are often characteristic of a particular taxon of the fungi.

• Sporangiospores: spores produced by a sporangium in many fungi such as zygomycetes.
• Zygospores: spores produced by a zygosporangium, characteristic of zygomycetes.
• Ascospores: spores produced by an ascus, characteristic of ascomycetes.
• Basidiospores: spores produced by a basidium, characteristic of basidiomycetes.
• Aeciospores: spores produced by a aecium in some fungi such as rusts or smuts.
• Urediospores: spores produced by a uredinium in some fungi such as rusts or smuts.
• Teliospores: spores produced by a telium in some fungi such as rusts or smuts.
• Oospores: spores produced by a oogonium, characteristic of oomycetes.
• Carpospores: spores produced by a carposporophyte, characteristic of red algae.
• Tetraspores: spores produced by a tetrasporophyte, characteristic of red algae.