Filicinae (Ferns), Ernst Haeckel
Kunstformen der Natur, 1904
The 92nd plate from Ernst Haeckel's Kunstformen der Natur (Art Forms of Nature), showing ferns.

A fern is any one of a group of about 20,000 species of plants classified in the phylum or division Pteridophyta, also known as Filicophyta.

Ferns are vascular plants differing from the more primitive lycophytes by having true leaves (megaphylls). They differ from seed plants (gymnosperms and angiosperms) in their mode of reproduction—lacking flowers and seeds. Like all other vascular plants, they have a life cycle referred to as alternation of generations, characterized by a diploid sporophytic and a haploid gametophytic phase. Unlike the gymnosperms and angiosperms, the ferns' gametophyte is a free-living organism.

Life cycle of a typical fern:
1. A sporophyte (diploid) phase produces haploid spores by meiosis;
2. A spore grows by mitosis into a gametophyte, which typically consists of a photosynthetic prothallus
3. The gametophyte produces gametes (often both sperm and eggs on the same prothallus) by mitosis
4. A mobile, flagellate sperm fertilizes an egg that remains attached to the prothallus
5. The fertilized egg is now a diploid zygote and grows by mitosis into a sporophyte (the typical "fern" plant).

Ernst Heinrich Philipp August Haeckel (February 16, 1834 – August 9, 1919), also written von Haeckel, was an eminent German biologist, naturalist, philosopher, physician, professor and artist who discovered, described and named thousands of new species, mapped a genealogical tree relating all life forms, and coined many terms in biology, including phylum, phylogeny, ecology and the kingdom Protista.

Vintage retro cute artistic nature pattern landscape realism fine art.