Sporogenesis in eusporangiate ferns: I. Monoplastidic meiosis in Angiopteris (Marattiales)

This is the first report of monoplastidic cell division in ferns. Angiopter is (Marattiales) undergoes the more primitive form of monoplastidic meiosis , while other ferns have evolved the polyplastidic type typical of seed pla nts. In monoplastidic cell division, the single plastid divides and serves as site of the microtubule organizing center (MTOC) for spindle formation r esulting in coordinated division of plastid, nucleus, and cytoplasm. In pla nts with polyplastidic cell division, the MTOC is diffuse and generally per inuclear. Monoplastidic cell division is seen as a plesiomorphic feature th at was inherited from algal ancestors containing a single plastid and modif ied through evolution. Monoplastidic meiosis occurs in all groups of bryoph ytes (although in only a few hepatics), Isoetes, Selaginella, certain gener ic segregates of Lycopodium, and in members of the Marattiales. It is not k nown to occur in psilophytes, Equisetum, leptosporangiate ferns, or seed pl ants.