1. In traditional classifications, any living organism of the kingdom Plantae, which includes the various groups of algae and the land plants, or embryophytes. Plants are distinguished from other organisms by their life cycles, in which haploid male and female organisms develop from spores produced by meiosis in the adult diploid organisms and produce gametes by mitosis; fertilization results in a diploid embryo that undergoes its early development in the haploid female. Most plants manufacture carbohydrates by photosynthesis, in which simple inorganic substances are built up into organic compounds. The radiant energy needed for this process is absorbed by chlorophyll, a complex pigment not found in animals. Plants also differ from animals in the possession of cell walls (usually composed of cellulose). Plants are immobile, as there is no necessity to search for food, and they respond slowly to external stimuli. For a classification of the plant kingdom, see Appendix 3.

2. Any member of a supergroup of eukaryotic organisms—the Archaeplastida—recognized on the basis of recent molecular data. Besides land plants, this assemblage contains the single-celled and colonial green algae (see chlorophyta), the more distantly related red algae (see rhodophyta), and some 13 species of single-celled algae—the Glaucophyta—whose chloroplasts are similar to cyanobacteria.

https://www.kew.org/science Open doors to the world of plants via the website of the Royal Botanic Gardens, Kew