Ferns are a diverse group with about 10,000 extant species. Sporangia clustered in sori on lower surfaces of leaves. Sori my be naked or covered by an indusium of false indusium. The spores are dispersed with the aid of special row of sporangium cells - the annulus. Gametophytes are photosynthetic and often heart-shaped.
All seed plants are heterosporous.
Microspores develop into male gametophytes called pollen grains, consisting of only a few cells. Ovules become seeds. Each seed contains an embryo, nutritive tissue, and a seed coat, which comes from the integument. Gametophytes are not free-living, they derive their nutrition from the parent sporophyte. Gymnosperms Gymnosperm seeds are naked - there are no flowers or fruit.