Seaweed is a leaflike marine spore plant with chlorophyll, autotrophic life and no embryo, which is called seaweed for short. They have the following three characteristics: (1) The whole algae has the functions of absorbing nutrients, carrying out photosynthesis and producing nutrients. Although some seaweeds have similar structures to the roots, stems and leaves of higher plants in appearance, they are essentially different in basic structure and function. In fact, regardless of its shape, functionally, the whole algae body of all algae is basically a single leaf, so it is called a "phyllosome" plant.

(2) The reproductive organs of algae are different from the seeds of higher plants, and most of them are single-celled spores or zygotes; Although the reproductive organs of some algae are multicellular, they are all directly involved in reproduction, unlike the reproductive organs of higher plants, which have reproductive and nutritional functions.

(3) The individual life history of algae begins with spores or zygotes and does not develop into multicellular embryos in the mother, which is different from the life history of higher plants.