Equisetaceae of Maine
(Kingdom Plantae, Monilophytes)

a project of
V. F. Thomas Co. - 167 Thorne Mountain Road - Canton, Maine  04221

(updated 29 January 2020)

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

Equisetum (horsetail)

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;
fertile; unbranched
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;
sterile; 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).