Microspores

Microspores are land plant spores that develop into male gametophytes, whereas megaspores develop into female gametophytes. The male gametophyte gives rise to sperm cells, which are used for fertilization of an egg cell to form a zygote. Microspores are structures that are part of the alternation of generations in many seedless vascular cryptogams, all gymnosperms and all angiosperms. Plants with heterosporous life cycles using microspores and megaspores arose independently in several plant groups during the Devonian period. Microspores are haploid, and are produced from diploid microsporocytes by meiosis.

This process is the most effective way of yielding haploid and double haploid plants through the use of male sex hormones. In the anther, after a microspore undergoes microsporogenesis, it can deviate towards embryogenesis and become star-like microspores. The microspore can then go one of four ways: Become an embryogenic microspore, undergo to organogenesis (haploid/double haploid plant), become a pollen-like structure or die.

The microspore consists of three different walled layers. The outer layer is called the , the next is the , and the inner layer is the endospore. The perispore is the thickest of the three layers while the exospore and endospore are relatively equal in width.

Microsporophylls bear microsporangia containing many microsporocytes that undergo meiosis, producing tiny microspores. Each microspore may become a male gametophyte consisting of a somewhat spherical antheridium within the microspore wall. Either 128 or 256 sperm cells with flagella are produced in each antheridium. In the ferns, the only heterosporous plants are aquatic or semi-aquatic, including the genera Marsilea,Regnellidium, Pilularia, Salvinia, and Azolla. This condition is also known in the lycopod genus Selaginella and in the quillwort genus Isoëtes.

...
Wikipedia