Calyptra in the context of Eucalyptus erythrocorys

In biology, a spore is a unit of sexual (in fungi) 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. They were thought to have appeared as early as the mid-late Ordovician period as an adaptation of early land plants.

Bacterial spores are not part of a sexual cycle, but are resistant structures used for survival under unfavourable conditions. Myxozoan spores release amoeboid infectious germs ("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.

Polytrichaceae is a common family of mosses. Members of this family tend to be larger than other mosses, with the larger species occurring in particularly moist habitats. The leaves have specialized sheaths at the base and a midrib that bears photosynthetic lamellae on the upper surface. These mosses are capable of sustaining high rates of photosynthesis in the presence of ample light and moisture. Unlike all other mosses, the hydroid-based vascular system of these mosses is continuous from stem to leaf and can extract water from the soil through transpiration. Species in this group are dioicous, though some are monoicous. In most species, the sporophytes are relatively large, the setae are rigid, and the calyptrae are hairy. Most species have nematodontous peristomes with 32–64 teeth in their sporangium; some early-diverging genera instead have a stopper mechanism, which consists of the apical section of the columella, that seals the mouth of the capsule shut prior to dehiscence.

Polytrichum is a genus of mosses — commonly called haircap moss or hair moss — which contains approximately 70 species that have a cosmopolitan distribution.The genus Polytrichum has a number of closely related sporophytic characters. The scientific name is derived from the Ancient Greek words polys, meaning "many", and thrix, meaning "hair". This name was used in ancient times to refer to plants with fine, hairlike parts, including mosses, but this application specifically refers to the hairy calyptras found on young sporophytes. A similar naming related to hair appears in Old Norse, haddr silfjar, "hair of Sif", goddess from Norse Mythology, wife of the god Thor. There are two major sections of Polytrichum species. The first — section Polytrichum — has narrow, toothed, and relatively erect leaf margins. The other — section Juniperifolia — has broad, entire, and sharply inflexed leaf margins that enclose the lamellae on the upper leaf surface.