A single mushroom will produce billions of spores. The spores grow long threads which spread through the growing medium. To reproduce sexually, a single thread fuses with another thread, but only if their sexes are compatible (Fungi have more than two sexes, in fact the Schizophyllum commune has 23,000 sexes). The fused threads form a single cell with two nuclei which only fuse once the mushroom has grown and eventually become the organ which produces the mushroom’s spores.
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