The Equisetaceae

The Horsetail Family

Equisetum hyemalespp.	Equisetum sylvaticum Woodland Horsetail.

The Equisetaceae are distributed on all continents except for Australia and New Zealand. They generally grow in moist, unforested areas near lakes and wetlands between 40 and 60 degrees north latitude. They tend to be colonizers. There is one genus and 15 species in the Horsetail Family.

Click here for a distribution map of Equisetum arvense in the U.S.A.

Vegetative Characters | Reproductive Characters | Diagnostic Characters | Economic Importance/Fun Facts | Evolutionary Adaptations and Relationships | Glossary of Terms | References and Links | Pictures

Vegetative Characters

• Areial part of plant is mostly jointed stem, range from 1m-8m in height
• Stems are hollow and ridged transversly along the internodes
• Leaves are very small usually less than 2cm long
• Leaves are whorled and fused at the base into sheaths-toothlike
• Leaves are microphylls and there can be up to 40 at a single node
• Equisetaceae is rhizomatous

Reproductive Characters

• Equistetaceae are homosporous
• Produce a strobilus with peltate sprorangiophores
• Stobilus usually terminal on the branch
• Hexagonal sporangiophores
• Sporangiophores are whorled in the stobili creating a terminal cone (see picture below)
• Spores are very distinct looking, they are spherical with 4-6 elaters
• An decrease in humidity causes the elaters to spring out, ejecting the spores from the sproragium
• There are usually 5-10 sporangia per sporophyll
• Plants can be perenial or annual

Diagnostic Characters

• Very small whorled leaves creating a fused sheath
• Jointed stems with ridging
• Spores with elaters

Economic Importance/Fun Facts

• The family has limited economic imporatacne
• There is silica in the stems which is an abrasive -it is believed that European settlers used the plants to scoure cookware
• Equi- means horse, setum- means tail

Evolutionary Adaptations and Relationships

• Fossil records of equisetophytes go back to the Devonian (408-360 MYA)
• Most abundant during the Carboniferous
• Microphylls evolved a second time in this group, all other leptosporangiate ferns have megaphylls
• Most likely monophyletic

Glossary of Terms

• homosporous-all spores produced are of equal size
• microphylls-leaves with a single strand of vascualr tissue, no branching
• elaters-structures found on surface of spore that expand when humidity decreases, aiding in ejection of spore from sprorangium and buoyancy when moving through the air
• peltate sporangiophore-hexagonal cap like structure with spores stored on underside

References and Links

• Hauke, Richard L., 1993. Flora of North America vol 2: Pteridophytes and Gymnosperms. Oxford Press New York, NY U.S.A.
• Judd et al., 1999. Plant Systematics: a phylogenetic approach. Sinauer Associates, Inc. Sunderland, MA U.S.A.
• Picture Sites:
• http://www.funet.fi/pub/sci/bio/life/plants/pteridophyta/sphenopsida/equisetaceae/equisetum/sp-2y.jpg
• http://www.borealforest.org/ferns/woodland_horsetail.jpg" alt="Image of Equisetaceae
• http://www.npwrc.usgs.gov/resource/othrdata/plntguid/species/maps/equiarve.jpg
• http://www.users.muohio.edu/smithhn/equisetum4%20copy.jpg
• http://www.funet.fi/pub/sci/bio/life/plants/pteridophyta/sphenopsida/equisetaceae/equisetum/sp-3x.jpg
• http://www.camag.ch/Images/equisetum.gif
• http://www.parametrix.com/Projects/bearevans/Horsetail.jp

Pictures

Cross section of a strobili with visible sprorangiophore.	Equisetum strobili-notice whorled leaves

Equisetum arvense	Equisetum arvense

For questions or feedback, contact: Catharine Calandra