A whole plant development stage (PO:0007033) that has as primary participant a whole plant (PO:0000003) during the interval between fertilization (or apogamy) and death.

A whole plant (PO:0000003) in the sporophyte development stage usually has twice the chromosome complement of a plant in the gametophytic phase, but may not in the case of apogamy. Examples of apogamy include both naturally occurring instances (such as sporophytes arising form haploid cells as in bryophytes or ferns) as well as in vitro instances (such as haploid embryo culture or in vitro fusion of non-gamete cells or protoplasts). During the sporophyte development stage, a plant may produce meiospores by meiosis.