What is a spore in the reproduction cycle of ferns?

Example: a fern of the Filicales order

In ferns, a spore is a haploid cell (=n) and is the means of dissemination; it germinates on the ground to form a gametophyte.

1. An adult sporophyte produces sporangia = small sacs in which spores (haploid=n) are formed by meiosis.

2. The opening of sporangia releases spores, which germinate on the ground and develop into gametophytes (haploid=n) or prothallia, that remain very small.

Spores (and sporangia) in fern groups may be

• all of the same type (case of the Filicales), or
• differentiated: microspores (in microsporangia) and macrospores (in macrosporangia) form male and female gametophytes respectively.

3. Gametophytes bear antheridia (that produce male gametes or antherozoids) and archegonia (that produce an egg cell).

4. The male gametes require the presence of water to swim to an archegonia and fertilize the egg, producing an embryo (2n).

5. The embryo grows out of the gametophyte plant as a diploid sporophyte (2n).