A species, or kind, is in botany the unit of classification.  It embraces all such individuals as may have originated in a common stock.  Such individuals bear an essential resemblance to each other, as well as to their common parent in all their parts.  E.g., the Cinnamon fern is a kind or species of fern with the fronds evidently of one kind, and of a common origin, and all producing individuals of their own kind by their spores or rootstocks.  When such individuals differ perceptibly from the type in the shape of the pinnae, or the cutting of the fronds, we have varieties as frondosum, incisum, etc.  Or if the difference is less striking the word form is used instead of variety, but in any given case opinions may differ in respect to the more fitting term.

A genus is an assemblage of species closely related to each other, and having more points of resemblance than of difference; e.g., the royal fern, the cinnamon fern, and the interrupted fern are alike in having similar spore cases borne in a somewhat similar manner on the fronds, and forming the genus Osmunda.  In like manner certain members of the clover group—­red, white, yellow, etc., make up the genus Trifolium.

Thus individuals are grouped into species and species are associated into genera, and the two groups are united to give each fern or plant its true name, the generic name being qualified by that of the species; as in the cinnamon fern Osmunda (genus), cinnamomea (species).

CHECK LIST OF THE FERNS OF NORTHEASTERN AMERICA

In the following list the first name is usually the one adopted in the text, and those that follow are synonyms.

Names printed in small capitals are those of the newer nomenclature, now adopted at the Gray Herbarium but not in the Manual.

ADIANTUM L.
1.  Adiantum Capillus-Veneris L.
2.  Adiantum pedatum L.
    Var.  ALEUTICUM RUPR.

ASPIDIUM SW.
3.  Aspidium Boottii.  Tuckerm. 
    Dryopteris Boottii. (Tuckerm.) Underw. 
    THELYPTERIS BOOTTII. (Tuckerm.) Nieuwl.
4.  Aspidium cristatum. (L.) Sw. 
    Dryopteris cristata. (L.) A. Gray. 
    THELYPTERIS CRISTATA. (L.) Nieuwl.
5.  Aspidium cristatum var.  Clintonianum.  D.C.  Eaton. 
    Dryopteris cristata var.  Clintoniana. (D.C.  Eaton.) Underw. 
    THELYPTERIS CRISTATA var.  CLINTONIANA. (D.C.  Eaton.) Weatherby.
6.  Aspidium cristatum x marginale.  Davenp.
7.  Aspidium Filix-mas. (L.) Sw. 
    Dryopteris Filix-mas. (L.) Sw. 
    THELYPTERIS FILIX-MAS. (L.) Nieuwl.
8.  Aspidium fragrans. (L.) Sw. 
    Dryopteris fragrans. (L.) Schott. 
    THELYPTERIS FRAGRANS. (L.) Nieuwl.
9.  Aspidium Goldianum.  Hook. 
    Dryopteris Goldiana. (Hook.) A. Gray. 
    THELYPTERIS GOLDIANA. (Hook.) Nieuwl.