In biology

Biology

Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...

, a microspore is a small spore

Spore

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 bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...

 as contrasted to the larger megaspore

Megaspore

Megaspores, also called macrospores, are a type of spore that is present in heterosporous plants. These types of plants have two spore types, megaspores and microspores. Generally speaking, the megaspore, or large spore, germinates into a female gametophyte, which is fertilized by sperm produced...

.

In botany, microspores develop into male gametophyte

Gametophyte

A gametophyte is the haploid, multicellular phase of plants and algae that undergo alternation of generations, with each of its cells containing only a single set of chromosomes....

s, whereas megaspores develop into female gametophytes. The combination of megaspores and microspores is found only in heterosporous organisms. In seed plants the microspores give rise to the pollen grains, and the megaspores are formed within the developing seed. Most plant

Plant

Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

s that reproduce by spore without seed only produce one class of spore. In the fern

Fern

A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...

s, the only heterosporous plants are aquatic or semi-aquatic, including the genera Marsilea

Marsilea

Marsilea is a genus of approximately 65 species of aquatic ferns of the family Marsileaceae.These small plants are of unusual appearance and do not resemble common ferns...

, Regnellidium

Regnellidium

Regnellidium is a monotypic genus of ferns of family Marsileaceae.The single living species, Regnellidium diphyllum, Two-leaf Water Fern, is native to South Eastern Brazil and adjacent regions of Argentina. It resembles its relatives from the genus Marsilea, but has 2-lobed leaves . This fern is...

, Pilularia

Pilularia

Pilularia is a genus of unusual ferns of family Marsileaceae distributed in North Temperate regions, Ethiopian mountains, and the southern hemisphere in Australia, New Zealand, and western South America....

, Salvinia

Salvinia

Salvinia, a genus in the family Salviniaceae, is a floating fern named in honor of Antonio Maria Salvini, a 17th Century Italian scientist. The genus was published by Séguier, in Pl. Veron. 3: 52. 1754. About ten species exist....

, and Azolla. This condition is also known in the lycopod genus Selaginella and in the quillwort genus Isoëtes.

In zoology, the small swarm-spores of Sarcodina are called microspores.