Equisetaceae - horsetail family
This family worldwide is composed of 15 species in one genus, Equisetum.
Maine is home to 8 species in 1 genus (hybrids excluded). If you already know which species you have or are interested in learning about, click on the appropriate species link below. Otherwise, to determine which genus that the plant in question falls into, refer to the table immediately below the species list.
Equisetum (8 species)
Equisetum arvense - field horsetail
Equisetum fluviatile - river horsetail
Equisetum hyemale ssp. affine - tall scouring-rush
Equisetum palustre - marsh horsetail
Equisetum pratense - meadow horsetail
Equisetum scirpoides - dwarf scouring-rush
Equisetum sylvaticum - wood horsetail
Equisetum variegatum - variegated scouring-rush
|red font = character state unique or nearly so||arial stem morphology||stem branching||central cavity size||cone tip||vallecular canals||char. 6|
|E. arvense||dimorphic||sterile: branched;
|1/4–1/3 stem diameter||blunt||present|
|E. fluviatile||monomorphic||branched, unbranched||≥4/5 stem diameter||blunt||absent|
|E. hyemale ssp. affine||monomorphic||mostly unbranched||2/3 ± stem diameter||sharp-pointed||present|
|E. palustre||monomorphic||branched||3/4 stem diameter||blunt||present|
|E. pratense||dimorphic||sterile: branched;
fertile: unbranched then branched
|1/6–1/3 stem diameter||blunt||present|
|E. scirpoides||mostly unbranched||absent||sharp-pointed||preent (3)|
|E. sylvaticum||dimorphic||fertile: unbranched then branched;
|1/6–1/3 stem diameter||rounded||present|
|E. variegatum||unbranched||1/3 stem diameter||sharp-pointed||present|
Equisetum arvense (field horsetail) may be mistaken for two different species if one observes the stems in early April and then later in the season. This is because the stems are dimorphic; that is, there are two different forms. In early April (on Mount Desert Island) the fertile stems appear. They are flesh-colored and have no branches (lower left three images). Later the sterile stems emerge (lower right, showing primarily sterile stems with some withering fertile stems).
(click on an image to enlarge)
Equisetum fluviatile (river horsetail) grows in shallow freshwater (image below).
(click on image to enlarge)
Equisetum hyemale ssp. affine - (tall scouring-rush) [information to be added]
Equisetum palustre (marsh horsetail) - [information to be added]
Equisetum pratense (meadow horsetail) - [information to be added]
Equisetum scirpoides (dwarf scouring-rush) - [information to be added]
(click on image to enlarge)
Equisetum sylvaticum (wood horsetail)
(click on images to enlarge)
Equisetum variegatum (variegatum scouring-rush) - [information to be added]
1. Taxonomy and nomenclature follow Flora Novae Angliae by Arthur Haines (2011, Yale University Press, ISBN 978-0-300-17154-9).