In angiosperms, meiosis in the sporophyte generation produces two kinds of spores. Link to a discussion of the alternation of gametophyte and sporophyte generations Both types of sporangia are formed in flowers. Some angiosperms are imperfect , having either microsporangia or megasporangia but not both. Monoecious plants have both types of imperfect flower on the same plant. Examples include willows, poplars, and the date palm.
Flowers develop from flower buds.
Each bud contains 4 concentric whorls of tissue. Link to a discussion of the genetic control of flower formation. Each stamen consists of a lobed anther , containing the microsporangia and supported by a thin filament Meiosis of the diploid microspore mother cells in the anther produces four haploid microspores . Each of these develops into a two-celled pollen grain . The two cells are the tube cell and the generative cell Carpels Carpels consist of a stigma , usually mounted at the tip of a style with an ovary at the base.