The Friends of the Wild Flower Garden, Inc.

Ferns of the Eloise Butler Wildflower Garden

The oldest public wildflower garden in the United States

Bracken Fern thumbnail

Common Name
Bracken Fern (Western Bracken Fern)


Scientific Name
Pteridium aquilinum (L.) Kuhn var. latiusculum (Desv.) Underw. ex A. Heller


Plant Family
Bracken Fern Family (Dennstaedtiaceae)

Garden Location
Upland - Fern grove


Prime Season
Spring to Autumn


Fern terms


Shape: Bracken Fern grows to 3 feet high, and usually in large colonies. It is the only large fern whose blade appears to be in 3 parts, plus the blades grow almost horizontally, forming a dense growth, very shady beneath.

Fronds: Sterile and fertile fronds are the same shape, with triangular blades that are divided into 3 almost equal size parts. These reflex from the stipe 45 to 60 degrees and can appear almost horizontal. They can be considered 3-pinnate at the base, where the first division is found - 1st division is the branching into 3 blade sections, each of which is considered a very large pinna, 2nd division is the large pinnae, 3rd division is the individual pinnules on the large pinnae and these large pinnules are further subdivided into lobes. The stipe is long and rigid with square edges, green at first and turning brown later. New fronds may form all season long.

Pinnae: The two lower pinnae, forming the base of the triangular blade, when taken together are large compared to the one above, but individually, the upper pinna is the largest. These lower two are almost opposite each other, distinctly stalked, and are cut to the costa into pinnules. The upper pinna has its upper pinnules spaced more tightly. The costa has a central groove with light fine hair.

Pinnules: Pinnules are variable in appearance, but arranged somewhat close together on the pinna and usually with narrowed tips. Fine veins fork from the central vein to the margins, which have a few very fine hair as does the under-rib of the pinnule. This is an identifying characteristic of var. latiusculum. The lobes on the upper pinnules are not cut to the costa but are pinnatifid and also are not opposite each other, but offset. Also the terminal segments of the pinnules (the narrowed tips) are only 2 to 4 times longer than wide in this variety vs var. pseudocaudatum where they are 6 to 12 times longer than wide.

Fertility: The sori form on the margin of the underside of the pinnules and the margin of the pinnule folds over to provide an indusium (more correctly called a false indusium), similar to the Maidenhair Fern. These turn brown at maturity of the sori.

Fiddleheads: These have green stems with fine hair and as the blade has three parts, when the fiddlehead unfolds it has the appearance of an eagle's claw which is where the species name aquilinum, is derived - from the Latin meaning "characteristic of eagle."


Habitat: Bracken Fern can aggressively colonize dry sites in full sun. The rhizome is deeply buried and survives most types of attempted destruction. It is also aggressive in forming new plants and a colony soon is made. This spreading from the rhizome is the normal way this fern produces new plants. Once established, it is very difficult to eradicate which is why it is sometimes termed the "weed of ferns". The shade provided by the re-flexing blades leaves little sun or moisture for anything beneath the blades. The plant is considered moderately toxic to livestock.

Names: The genus Pteridium, is from the Greek pteris, for 'fern', which in turn was derived from pteron, meaning 'wing', referring to the frond shape. The species is explained above. An older name is Pteridium latiusculum (Desv.) Hieron. The authorship is quite complex - see note at bottom of the page. In Eloise Butler's time the name frequently used was Pteris aquilina, but by the time of Martha Crone's 1951 Garden plant census the current name was in use.

See bottom of page for notes on the Garden's planting history, distribution in Minnesota and North America, lore and other references.

Bracken Fern Bracken Fern Fiddlehead Bracken Fern Fiddlehead

Above: 1st photo A stand of young fronds. 2nd & 3rd photos - Emerging fiddlehead of Bracken Fern. As it unfolds the 3 arms of the future blade create the appearance of an eagle claw, from which comes the species name.

Below: The pinnules of a large lower pinna are cut through to the costa near the base of the pinnule but not so toward the tip and not on the smaller upper pinnules (photo further below).

Bracken Fern Frond

Below: 1st photo - The blade reflexes from the stipe giving the blades a 45 to 60 degree spreading appearance. 2nd photo - The point of the stipe where the frond separates into 3 blade sections (each a large pinna) - left, right and up. The right and left laterals are slightly offset from each other. Note the square edges of the stipe leading up to the separation point.

Bracken Fern frond Stem joint

Below: 1st photo - the sori form on the margins of the undersides of the pinnules and the margin of the pinnule folds over covering them forming a false indusium. Note the fine hair on the margins and the sparse hair on the rib. 2nd photo - As the season progresses, the false indusium falls away exposing the sori.

sori sori

Below: 1st photo - The upper lobes on the pinnules are not opposite each other and not cut as deeply. 2nd photo - Fine veins fork from the central vein of each pinnule to the margins.

Pinna near blade tip pinnule veins

Below: 1st photo - A fern viewed from above with the 2 lateral blades each smaller than the center (Upward ascending) blade, but together they are longer. Also note the lowest pinnules on each pinna are much larger than those toward the tips. 2nd photo - This young frond clearly shows the 2 lateral divisions closest to the base and the larger upper division.

Plant young leaf
Bracken Fern plant


Notes: Eloise Butler considered Bracken Fern to be indigenous to the Garden. Although she makes no mention of it in her Garden Log in the first years of the Garden, she listed it as one of ten species of ferns that were indigenous to the Garden when she submitted an essay on ferns and fern allies to the Agassiz Association in 1915. She wrote in 1915 It is rapidly spreading, although when the garden started in 1907 it was not in evidence and I recall that three of the teachers of botany tried and failed to dig up a root of it to transplant in the garden". In a follow-up essay 4 years later she noted that is was "the least abundant, but it is rapidly increasing on the sides of the knoll on which my office stands." {Entire 1919 essay} Several new plants were planted as recently as 2006. A good patch of them is found at the entrance to the Fern Glen. Thirty-six of these were planted in there in 1956 when Martha Crone developed the Fern Glen.

In North America Bracken Fern is found from the Dakotas, Oklahoma and Texas eastward to the coast and also in Montana and Colorado and in the Canadian southern provinces except Saskatchewan. Within Minnesota it is found in most of the state except the SW Quadrant. There is only one species within this genus, but it is a worldwide genus with a number of varieties. There are several accepted varieties of these in North America but only two in the eastern half of the continent and the one treated here is considered the native variety of Minnesota. The second variety found in the eastern half of North America is var. pseudocaudatum The variety found in the Western part of North America is var. pubescens. It has abundant hair on the underside of the blades.

Authorship: The authors of the botanical classification of this species and its history are quite complex. Pteridium aquilinum was originally named by Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy. That's the '(L.)'. Next, ‘Kuhn’ is for Friedrich A. Maximilian Kuhn (1842-1894), German Botanist who revised Linnaeus's description in 1879. In the variety latiusculum, ‘Desv.’ is for Nicaise Auguste Desvaux (1784-1856), French botanist and director of the botanical garden in Angers, who wrote several volumes on plants of the Marne and Loire regions. He wrote his characteristics for Pteridium latiuscula in 1827. That became Pteridium latiusculum (Desv.) Hieron. by the work, in 1914, of Georg Hans Emmo Wolfgang Hieronymus, (1846-1921), a European botanist (his name now dropped from the published botanical name) and that species has now been consolidated as a variety of Pteridium aquilinum. The current description is by 'Underw.' which refers to Lucien Marcus Underwood (1853-1907), American botanist and mycologist. One of his works was “Our Native Ferns and How to Study Them." His work was updated in Heller's Catalogue of 1909. 'A. Heller’ is for Amos Arthur Heller (1867-1944), American botanist, who collected extensively in California and Puerto Rico, and created several extensive herbarium collections.

References and site links

References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.

graphicIdentification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.