Flora of North America species comparison

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Adiantum capillus-veneris

Adiantum

black maidenhair fern, common maidenhair, southern maiden-hair, southern maidenhair fern, Venus hair, Venus hair fern, Venus's-hair fern

maidenhair fern
Habit Plants terrestrial or on rock.
Stems

short-creeping;

scales golden brown to medium brown, concolored, iridescent, margins entire or occasionally with single broad tooth near base.

short- to long-creeping or suberect, branched;

scales deep tawny yellow to dark reddish brown [black], concolored or bicolored, linear-lanceolate to lanceolate, margins entire, erose-ciliate, or minutely dentate.
Leaves

lax-arching or pendent, closely spaced, 15–75 cm.

monomorphic to somewhat dimorphic, densely clustered to closely spaced [distant], 15–110 cm.
Petiole

0.5–1.5 mm diam., glabrous, occasionally glaucous.

chestnut brown to dark purple or blackish, with single groove adaxially, glabrous, hispid, or strigose, with 1 or 2 vascular bundles.
Blade

lanceolate, pinnate, 10–45 × 4–15 cm, glabrous, gradually reduced distally;

proximal pinnae 3(–4)-pinnate;

rachis straight to flexuous, glabrous, not glaucous.

lanceolate, ovate, trowel-shaped, or fan-shaped, 1–4(–9)-pinnate proximally, membranaceous to papery, both surfaces commonly glabrous (2 species with scattered hairs), adaxially dull or shiny, not striate;

rachis straight or flexuous.
Ultimate segments

various, generally cuneate or fan-shaped to irregularly rhombic (plants in American southwest occasionally with segments nearly round), about as long as broad;

base broadly to narrowly cuneate;

margins shallowly to deeply lobed, incisions 0.5–7 mm, occasionally ± laciniate, sharply denticulate in sterile segments;

apex rounded to acute.

subsessile to short-stalked (stalks terminating in cupulelike swelling at base of pinna in A. tenerum), round, fan-shaped, rhombic, or oblong, 3–29 mm wide;

base truncate to cuneate, free from costa;

stalk dark, often lustrous;

fertile segments with marginal lobes recurved to form false indusia.
Veins

of ultimate segments conspicuous, free, ± dichotomously forking near base and well above segment base [anastomosing in a few tropical species], parallel distally.
Indusia

transversely oblong or crescent-shaped, 1–3(–7) mm, glabrous.

False indusia

light gray-green or brown to dark brown, narrow, 0.6–1 mm wide, marginal, concealing sporangia until sporangia dehisce.
Sporangia

submarginal, borne along or sometimes also between veins on abaxial surface of false indusium, paraphyses and glands absent.
Spores

mostly 40–50 µm diam. 2n = 120.

yellow or yellowish brown, tetrahedral-globose, trilete, rugulate to rugose or tuberculate, equatorial ridge absent.
Segment

stalks 0.5–3.5 mm, dark color extending into segment base.

x

= 29, 30.

Adiantum capillus-veneris

Adiantum
Phenology Sporulating spring–summer.
Habitat Moist calcareous cliffs, banks, and ledges along streams and rivers, walls of lime sinks, canyon walls (in the American southwest), around foundations, on mortar of storm drains
Elevation 0–2500 m (0–8200 ft)
Distribution
from FNA
AL; AR; AZ; CA; CO; FL; GA; KY; LA; MO; MS; NC; NM; NV; OK; SC; SD; TN; TX; UT; VA; BC; Mexico; Central America; West Indies; South America in Venezuela; Peru; tropical to warm temperate regions in Eurasia and Africa
[WildflowerSearch map]
[BONAP county map]
from USDA
Nearly worldwide except at latitudes greater than 60°
[BONAP county map]
Discussion

No evident pattern to morphologic variation in the species is discernible, although a number of segregate species and infraspecific taxa have been recognized within North American Adiantum capillus-veneris. In the Eastern Hemisphere, the species is diploid, with 2n = 60 (I. Manton 1950). Several tetraploid counts have been reported from North America (W. H. Wagner Jr. 1963). Spore-measurement data suggest, however, that the polyploid cytotype may not be widely distributed. Further investigation is needed to determine whether Adiantum capillus-veneris populations in North America are conspecific with those in Eurasia and Africa.

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

Most diverse in Andean South America, Adiantum is primarily a tropical genus; of the nine species occurring in the flora, A. melanoleucum, A. tenerum, and A. tricholepis are strictly subtropical. Adiantum hispidulum occurs only as an escape from cultivation. The genus is absent from dry areas in the interior of the continent.

Adiantum is a very clearly circumscribed genus of ferns, the character state "sporangia borne on abaxial surface of false indusium" being both necessary and sufficient to define it. Within this large and widespread genus, however, species relationships are mostly unknown. An evolutionary classification of the group is indeed much needed (R. M. Tryon and A. F. Tryon 1982).

Species ca. 150–200 (9 in the flora).

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Key
1. Segments at middle of penultimate divisions of blades ± fan-shaped, rhombic, transversely oblong, or nearly round, about as long as broad.
→ 2
1. Segments at middle of penultimate divisions of blades ± oblong or long-triangular, at least 2 times as long as broad (rarely, reniform).
→ 5
2. Dark color of stalks extending into base of ultimate segments.
A. capillus-veneris
2. Dark color of stalks ending ± abruptly at base of ultimate segments.
→ 3
3. Segment stalks terminating in small, cupulelike swelling at base of ultimate segments.
A. tenerum
3. Segment stalks not terminating in small, cupulelike swelling at base of ultimate segments.
→ 4
4. Ultimate segments glabrous.
A. jordanii
4. Ultimate segments hirsute.
A. tricholepis
5. Rachises hispid or strigose; blades pinnate (occasionally pseudopedate in Adiantum hispidulum).
→ 6
5. Rachises glabrous; blades pseudopedate.
→ 7
6. Ultimate segments with scattered multicelled hairs; rachises hispid; false indusia ± round.
A. hispidulum
6. Ultimate segments glabrous; rachises strigose; false indusia crescent-shaped.
A. melanoleucum
7. Segments at middle of penultimate divisions of blades ± oblong; leaves lax-arching, blades fan-shaped.
→ 8
7. Segments at middle of penultimate divisions ± long-triangular or reniform; leaves arching to stiffly erect, blades fan-shaped to funnel-shaped.
→ 9
8. Segments at middle of penultimate divisions of blades generally less than 3.2 times as long as broad, apices with rounded, crenulate or crenate-denticulate lobes, lobes separated by shallow sinuses 0.1–2(–3.7) mm, segment stalks ca. 0.6–0.9 mm.
A. pedatum
8. Segments at middle of penultimate divisions usually more than 3.2 times as long as broad, apices with sharply denticulate, angular lobes, lobes separated by deep sinuses 0.6–4 mm, segment stalks to 0.6 mm.
A. aleuticum
9. Central ultimate segments on stalks less than 0.9 mm; false indusia mostly less than 3.5 mm.
A. aleuticum
9. Central ultimate segments on stalks generally greater than 0.9 mm; false indusia mostly exceeding 3.5 mm.
A. viridimontanum
Source FNA vol. 2. FNA vol. 2. Author: Cathy A. Paris.
Parent taxa Pteridaceae > Adiantum Pteridaceae
Sibling taxa
A. aleuticum, A. hispidulum, A. jordanii, A. melanoleucum, A. pedatum, A. tenerum, A. tricholepis, A. viridimontanum
Subordinate taxa
A. aleuticum, A. capillus-veneris, A. hispidulum, A. jordanii, A. melanoleucum, A. pedatum, A. tenerum, A. tricholepis, A. viridimontanum
Synonyms A. capillus-veneris var. modestum, A. capillus-veneris var. protrusum, A. capillus-veneris var. rimicola
Name authority Linnaeus: Sp. Pl. 2: 1096. (1753) Linnaeus: Sp. Pl. 2: 1094. 1753; Gen. Pl. ed 5, 485. (1754)
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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