page_title: Spore
section_title: External anatomy
hierarchical_section_title: Spore / External anatomy
context_page_description: In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, fungi and protozoa. Bacterial spores are not part of a sexual cycle but are resistant structures used for survival under unfavourable conditions. Myxozoan spores release amoebulae into their hosts for parasitic infection, but also reproduce within the hosts through the pairing of two nuclei within the plasmodium, which develops from the amoebula.
  Spores are usually haploid and unicellular and are produced by meiosis in the sporangium of a diploid sporophyte. Under favourable conditions 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 form a zygote which develops into a new sporophyte. This cycle is known as alternation of generations.
context_section_description: Under high magnification, spores often have complex patterns or ornamentation on their exterior surfaces. A specialized terminology has been developed to describe features of such patterns. Some markings represent apertures, places where the tough outer coat of the spore can be penetrated when germination occurs. Spores can be categorized based on the position and number of these markings and apertures. Alete spores show no lines. In monolete spores, there is a single narrow line (laesura) on the spore. This indicates the mother spore split into four along a vertical axis. In trilete spores, each spore shows three narrow lines radiating from a center pole. This shows that four spores shared a common origin and were initially in contact with each other forming a tetrahedron. A wider aperture in the shape of a groove may be termed a colpus. The number of colpi distinguishes major groups of plants. Eudicots have tricolpate spores (i.e. spores with three colpi).
caption: Tricolpate pollen of Ricinus
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