Phylum Sphenophyta
- Includes phylum description, and links to images of members of the Equisetaceae (horsetails).
- http://www.science.siu.edu/landplants/Sphenophyta/sphenophyta.html

Equisetaceae
- General description of this family of terrestrial, herbaceous, homosporous vascular plants, comprising a single genus with about 15 species. Includes photos of several Equisetum species.
- http://www.botany.hawaii.edu/faculty/carr/equiset.htm

Horsetails - Equisetaceae
- Brief description of the horsetail family, including descriptions of several Equisetum species.
- http://bodd.cf.ac.uk/BotDermFolder/BotDermE/EQUI.html