Seed plants' tiny gametophytes
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Suboptimal design > Seed plants' tiny gametophytes
Land plants practice alternation of generations between a diploid sporophyte phase and a haploid gametophyte phase; these phases produce spores and gametes, respectively. The more primitive plants, like mosses, liverworts, and ferns, have prominent sporophyte and gametophyte phases, but seed plants are nearly all sporophyte, having only microscopic gametophytes with only a few cells. The female gametophytes live inside of the parent plant's female reproductive parts (female cone, pistil, ...), while the male gametophytes are released inside of pollen grains from the parent plant's male reproductive parts (male cone, stamen, ...). When a pollen grain arrives at a compatible female reproductive part, it sprouts a pollen tube that contains the sperm-cell nuclei. This tube grows inside that part toward an embedded female gametophyte, where it fertilizes an egg cell.
This is clearly convergence toward the usual animal state of affairs of being all-diploid except for the gametes; the tiny gametophytes are essentially vestigial, and could easily be done without.
