Ulva goes through an isomorphic alternation of generations. Adult gametophytes produce only female or male gamets, which are positively phototactic, and move with flagella. They are released in swarms coordinated by lunar cycles and tides. When the zygote is formed it becomes negatively phototactic and swims to the bottom to settle, and germinates within a few days. The haploid phase of the life cycle (the sporophyte), produces sporophytes which, like the gametes, are also motile using a set of four flagella to swim (Lee 2008; Guiry and Guiry 2011).
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