Pteridophyta - ferns (weeds)
The pteridophytes (also called monilophytes) include the ferns and horsetails. The group contains more than 10,000 species of plants which do not produce flowers or seeds. Instead, they form haploid, single-celled spores. These germinate and form a tiny plant-like structures (1-2 mm large), the prothallus, which produces sexual organs, often both sperm and eggs on the same prothallus. Eggs are fertilized by a flagellate sperm and grow into a new diploid plant.
Ferns include several important weeds, usually introduced and invasive species. Some are terrestrial like Lygodium microphyllum, the old world climbing fern, while others are aquatic, like Salvinia molesta, a floating fern.
The following families of weeds are currently included: