Alternation of generations
Alternation of generations is the predominant type of life cycle in plants and algae. In plants both phases are multicellular: the haploid sexual phase – the gametophyte – alternates with a diploid asexual phase – the sporophyte.
Gametophyte of the fern Onoclea sensibilis (flat thallus, bottom) with a descendant sporophyte beginning to grow from it (small frond, top)
Gametophyte of Mnium hornum, a moss
Sporophyte of Lomaria discolor, a fern
Gametophyte of Pellia epiphylla with sporophytes growing from the remains of archegonia
Plants are the eukaryotes that form the kingdom Plantae; they are predominantly photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with cyanobacteria to produce sugars from carbon dioxide and water, using the green pigment chlorophyll. Exceptions are parasitic plants that have lost the genes for chlorophyll and photosynthesis, and obtain their energy from other plants or fungi.
Image: Frühling blühender Kirschenbaum
Image: Micrasterias radiata
Image: Red Moss
Image: Glaucocystis nostochinearum