Flora of North America species comparison

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Pteridium aquilinum

Pteridium

bracken, bracken fern, fougère-aigle commune, western brackenfern

bracken, brackenfern, brake, brake-fern
Habit Plants terrestrial, often forming colonies or thickets.
Stems

subterranean, slender, long-creeping;

hairs pale to dark, jointed;

scales absent;

true vessels present (absent in other Dennstaedtiaceae genera in the flora).
Leaves

widely spaced, broadly deltate, 0.5–4.5 m. Petiole glabrous to short-hairy, without prickles, with stem buds near base, vascular bundles numerous, U- or O-shaped in cross section.
Petioles

scattered along creeping stems, 0.3–3.5 m, shallowly to deeply grooved adaxially, base not strongly distinct from stem.

Blade(s)

broadly deltate, papery to leathery, sparsely to densely hairy abaxially, rarely glabrous.

2–4-pinnate, rachis and costae grooved adaxially;

rachis without prickles;

nectaries at base of proximal and sometimes distal pinnae.
Segments

alternate, numerous.

pinnately divided, ultimate segments ovate to oblong to linear, base extending proximally on costae (decurrent) or proximally (surcurrent), margins entire.
Pinnae

often opposite to subopposite [alternate];

proximal pinnae often prolonged basiscopically, each proximal pinna nearly equal to distal part of leaf in size and dissection (except in var. caudata).

Veins

free or joined at margin by commissural vein beneath sori, pinnately 2–3-forked.
Sori

± continuous, covered by recurved, outer false indusium and obscure, extrorse, inner true indusium.
Spores

tetrahedral-globose, trilete, very finely granulate.
x

= 26.

Pteridium aquilinum

Pteridium
Distribution
from FNA
AK; AL; AR; AZ; CA; CO; CT; DC; DE; FL; GA; IA; ID; IL; IN; KY; LA; MA; MD; ME; MI; MN; MO; MS; MT; NC; ND; NH; NJ; NM; NV; NY; OH; OK; OR; PA; RI; SC; SD; TN; TX; UT; VA; VT; WA; WI; WV; WY; AB; BC; MB; NB; NF; NS; ON; PE; QC; Almost worldwide
[WildflowerSearch map]
[BONAP county map]
from USDA
Almost worldwide
[BONAP county map]
Discussion

In accord with the most recent revision (R. M. Tryon 1941) of the genus, Pteridium is treated here as a single widespread species composed of two subspecies with 12 varieties. So treated, it is probably the most widespread species of all vascular plants, with the exception of a few annual weeds (F. H. Perring and B. G. Gardner 1976). The plants are generally aggressive, invading disturbed areas as weeds in pastures, cultivated fields, and roadsides. In Europe, it was harvested and burned to produce potash. Although croziers are eaten in many temperate cultures, bracken has been shown to contain thiaminase (and other compounds with mutagenic and carcinogenic properties).

Disagreement exists among taxonomists regarding the rank that should be accorded to the taxa treated herein as varieties. In a survey of the genus, C. N. Page (1976) noted uniform chromosome numbers and flavonoid compositions of the varieties. D. B. Lellinger (1985) separated the genus into at least two species based on morphology, recognizing as species the subspecies of R. M. Tryon (1941). J. T. Mickel and J. M. Beitel (1988) reported sympatric occurrence in Mexico of three taxa that maintained consistent characteristics and only rarely produced plants with combined characteristics. They suggested that these three taxa should be considered as species that occasionally hybridize. P. J. Brownsey (1989) reported that two different brackens in Australia formed sterile hybrids and should be treated as species. Modern systematic studies are needed to evaluate the status and rank of the four North American varieties. As treated below, Pteridium aquilinum var. pubescens, var. latiusculum, and var. pseudocaudatum are in subsp. aquilinum, and var. caudatum is in subsp. caudatum (Linnaeus) Bonaparte.

Varieties 12 (4 in the flora).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Species 1 (1 species, 4 varieties in the flora).

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Key
1. Fertile ultimate segments only decurrent or more decurrent than surcurrent, mostly 1-2 mm wide; hairs on abaxial surface of blades abundant, straight, stiff, subappressed to spreading.
var. caudatum
1. Fertile ultimate segments adnate or equally decurrent and surcurrent, mostly 3-6 mm wide; hairs on abaxial surface of blades abundant to sparse, twisted and flexible, if abundant then lax, spreading.
→ 2
2. Pinnules at nearly 90º angle to costa; outer indusium pilose on margin and often on surface; hairs on abaxial surface of blades abundant, lax, and spreading.
var. pubescens
2. Pinnules at 45º -60º angle to costa; outer indusium glabrous; hairs on abaxial surface of blades sparse or blades nearly glabrous.
→ 3
3. Terminal segments of pinnules 2-4 times longer than wide; segment margins and abaxial surface of blade midrib and costae shaggy.
var. latiusculum
3. Terminal segments of pinnules ca. 6-15 times longer than wide; segment margins and abaxial surface of blade midrib and costae sparsely pilose to glabrous.
var. pseudocaudatum
Source FNA vol. 2. FNA vol. 2. Authors: Carol A. Jacobs, James H. Peck.
Parent taxa Dennstaedtiaceae > Pteridium Dennstaedtiaceae
Subordinate taxa
P. aquilinum var. caudatum, P. aquilinum var. latiusculum, P. aquilinum var. pseudocaudatum, P. aquilinum var. pubescens
P. aquilinum
Synonyms Pteris aquilina
Name authority (Linnaeus) Kuhn: in Decken, Reisen Ost-Afrika 3(3): 11. (1879) Gleditsch ex Scopoli: Fl. Carniol. 169. (1760)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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