Pollen as large as about 90–100 µm. In angiosperms, during flower development the anther is composed of a mass of cells that appear undifferentiated, except for a partially differentiated dermis. As the flower develops, four groups of sporogenous cells form within the anther. The fertile sporogenous cells are surrounded by layers of sterile cells that grow into the wall of the pollen sac. Some of the cells grow into nutritive cells that supply nutrition for the microspores that form by meiotic division from the sporogenous cells. In a process called microsporogenesis, four haploid microspores are produced from each diploid sporogenous cell
Pollen DNA barcoding that has grown in popularity due to the decreased costs associated with "next generation sequencing" (NGS) techniques and is being continually improved in efficiency including through the use of a dual-indexing approach. Some of the other major advantages include the savings in time and resources compared to microscopic identification. Identifying pollen is time consuming involving spreading pollen on a slide, staining the pollen to improve visibility, then focusing in on individual pollen grains and identifying them based on size, shape, as well as the shape and number of pores. If a pollen reference library is not available, then pollen has