Ulva and Polysiphonia both have alternation of generations types of life cycles. Spirogyra produces motile, flagellated gametes like most other green algae. Most brown algae are found in cold ocean water. Diatoms have silicon in their cell walls. Red tides are caused by exploding populations of diatoms.
Red algae are important as a source of commercial agar.
In the large kelps, the plant you see is the gametophyte generation. Archegoniophores and antheridiophores are produced by some liverworts. Male mosses produce pollen. Acetabularia is a brown alga. Paramylon is the food storage carbohydrate of the green algae.