OPHA clade, species that are native to the American continent and have one type of sporophyll in the form of a megaspore network.
32.
The female gametophytes in the conelet develop so slowly that the megaspore does not go through free-nuclear divisions until autumn of the 3rd year.
33.
The tetrasporic pattern is characterized by cell plates failing to form after either meiosis 1 or 2, and results in one four-nucleate megaspore.
34.
One of these four cells ( megaspore ) then undergoes three successive mitotic divisions to produce an immature embryo sac ( megagametocyte ) with eight haploid nuclei.
35.
This pattern is characterized by cell plate formation after meiosis 1 & 2, which results in four one-nucleate megaspores, of which three degenerate.
36.
The bisporic pattern is characterized by cell plate formation only after meiosis 1, and results in two two-nucleate megaspores, of which one degenerates.
37.
The megaspore undergoes several mitotic divisions to develop into a female gametophyte ( for example the seven-cell / eight-nuclei embryo sac in flowering plants ).
38.
If so, " Aarabia " had megaspores and could be the earliest known plant with'heterospory', i . e . two distinct sizes of spore.
39.
They bear sporocarps of two types, either megasporangia that are few in number ( approximately 10 ), each with single megaspore, or many microsporangia, each with 64 microspores.
40.
These have creeping rhizomes, styles divided at their apices, and an embryo-sac of the " Polygonum "-type with a simple megaspore and triploid endosperm.
