Reproduction Fungi can reproduce asexually, primarily by releasing spores that are adapted to travel through air and water. Simply breaking off a hypha or budding off a cell can also serve as asexual reproduction.

Most fungi also can reproduce sexually. Figure 21–17 shows the life cycle of a type of bread mold, a fungus called Rhizopus stolonifer. Sexual reproduction in fungi often involves two different mating types. In Rhizopus, as in most fungi, gametes of both mating types are about the same size and are not usually called male and female. Instead, one mating type is called “+” (plus) and the other “–” (minus). When hyphae of opposite mating types meet, they start the process of sexual reproduction by fusing, bringing + and–nuclei together in the same cell. The + and–nuclei form pairs that divide in unison as the mycelium grows. Many of the paired nuclei fuse to form diploid zygote nuclei, which go through meiosis to make haploid spores. Each spore has a different combination of parental genes, and each can make a new mycelium.

Diversity of Fungi More than 100,000 species of fungi are known. Of course, they all share the characteristics that define them as fungi, but they differ from one another in important ways. Biologists have used these similarities and differences, along with DNA comparisons, to place the fungi into several distinct groups. The major groups of fungi differ from one another in their reproductive structures, as summarized in Figure 21–18.

FIGURE 21–18 The Major Phyla of Fungi The table summarizes the main differences among the four major phyla of fungi. Infer Would you expect to find chytrids in aquatic or terrestrial habitats? Explain your answer.

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