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 know which species you have or are interested in learning about, click on the appropriate link from the species list below. Otherwise, to determine which species your horsetail/scouring-rush is, refer to the table below the species list.

   Equisetum (8 species)
      Equisetum arvense - field horsetail
      Equisetum fluviatile - river horsetail
      Equisetum hyemale ssp. affine - tall scouring-rush
      Equisetum palustris - marsh horsetail
      Equisetum pratense - meadow horsetail
      Equisetum scirpoidea - 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; fertile unbranched	1/4–1/3 of stem diameter	blunt	present
E. fluviatile	monomorphic	unbranched or with a few irregular branches	≥4/5 of stem diameter	blunt	absent
E. hyemale ssp. affine	monomorphic	mostly unbranched	approximately 2/3 of stem diameter	sharply pointed	present
E. palustre	monomorphic	branched	3/4 of stem diameter	blunt	present
E. pratense	dimorphic	sterile branched; fertile unbranched when young, later branched	1/6–1/3 of stem diameter	blunt	present
E. scirpoides		mostly unbranched	absent	sharply pointed	present (3)
E. sylvaticum	dimorphic	fertile unbranched when young, later branched; sterile branched	1/6–1/3 of stem diameter	rounded	present
E. variegatum		unbranched	1/3 of stem diameter	sharply pointed	present

Equisetum (horsetail, scouring-rush)
[information to be added]

Equisetum arvense (field horsetail) may be mistaken as two different species if one observes the stems in early April and then later in the season. This is becausee the stems are dimorphic; i.e., there are two different forms). Early in the season the fertile stems appear. They are flesh-colored and are unbranched (lower left three images). Later the sterile stems emerged emerge, their ascending branches soon spreading out (lower right image, showing some withering fertile stems).
               
   (click on an image to enlarge)

Equisetum fluviatile (river horsetail) grows in shallow water (image below).
   
   (click on an image to enlarge)

Equisetum hyemale ssp. affine (tall scouring-rush)
         
   (photos by Kevin Stone; click on an image to enlarge)

Equisetum palustre (marsh horsetail) - [information to be added]

Equisetum pratense (meadow horsetail) - [information to be added]

Equisetum scirpoides (dwarf scouring-rush)
   
   (click on an image to enlarge)

Equisetum sylvaticum (wood horsetail)
   
   (click on an image to enlarge)

Equisetum variegatum (variegated scouring-rush) - [information to be added]

Note:
   1. Taxonomy and nomenclature follow Flora Novae Angliae by Arthur Haines (2011, Yale University Press, ISBN 978-0-300-17154-9).