Independent male and female gametophytes are present in

The correct option is Sphagnum.

To understand why this is the correct answer, let us break down the concepts of alternation of generations, gametophytes, and sporophytes across different plant groups:
1. Gametophyte vs. Sporophyte: In the plant life cycle, there is an alternation of generations between a haploid gametophyte phase (which produces gametes) and a diploid sporophyte phase (which produces spores).
2. Bryophytes (e.g., Sphagnum): Sphagnum is a bryophyte (peat moss). In bryophytes, the dominant, photosynthetic, and independent phase of the life cycle is the haploid gametophyte. The sporophyte is physically dependent on the gametophyte for nutrition and support. Thus, Sphagnum possesses an independent gametophyte.
3. Gymnosperms (e.g., Pinus): In gymnosperms like Pinus, the dominant phase is the diploid sporophyte. The male and female gametophytes are highly reduced, microscopic structures that remain completely dependent on and enclosed within the parent sporophyte tissues (pollen grains and ovules, respectively) for their nutrition and development. They do not have an independent free-living existence.
4. Angiosperms (e.g., mustard and castor): Mustard and castor are flowering plants (angiosperms). Similar to gymnosperms, angiosperms have a highly reduced gametophyte generation (the pollen grain represents the male gametophyte, and the embryo sac represents the female gametophyte). These gametophytes are entirely dependent on the dominant sporophyte plant body and are not free-living or independent.

Therefore, among the given options, only the bryophyte Sphagnum has independent, free-living male and female gametophytes.