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Boston swordfern, sword fern, wild Boston fern

Boston fern, swordfern

Habit Plants terrestrial, epiphytic, or on rock.
Stem(s)

scales spreading, concolored.

ascending to erect, bearing wiry stolons and sometimes underground tubers.

Leaves

4–15 × 0.5–1.2 dm.

monomorphic, evergreen.

Petiole

0.2–4 dm, sparsely to moderately scaly;

scales spreading, pale brown to reddish brown, concolored.

ca. 1/10–1/2 length of blade, base not swollen;

vascular bundles more than 3, arranged in an arc, ± round in cross section.

Blade

glabrous, sparsely to moderately scaly abaxially near costae and adaxially.

narrowly elliptic to linear-lanceolate, 1-pinnate (to 4–5-pinnate in various cultivated forms), very gradually reduced distally to minute pinnatifid apex, often seemingly indeterminate with apex never expanded, herbaceous to papery.

Pinnae

articulate to rachis, sometimes deciduous, segment (pinna) margins entire, crenulate, or biserrate;

proximal pinnae (usually several pairs) slightly to greatly reduced, sessile, equilateral or inequilateral with basiscopic base excised and often an acroscopic basal auricle;

costae adaxially grooved, grooves not continuous from rachis to costae;

indument of linear-lanceolate scales and sometimes multicellular hairs on abaxial and sometimes adaxial surfaces.

Veins

free, forked.

Indusia

reniform to horseshoe-shaped, attached at narrow or broad sinus, 1–1.7 mm wide.

Sori

± round;

indusia round-reniform and with deep sinus to semicircular with broad sinus or lunate without sinus and seemingly laterally attached, persistent.

Spores

brownish, tuberculate to rugose.

Tubers

absent.

Rachis

2.4–16.3 dm, points of pinna attachment 7.3–21 mm apart;

scales moderately spaced, pale to dark brown, essentially concolored or margin indistinctly paler;

hairs absent.

Central

pinnae deltate-oblong, slightly to distinctly falcate, 2.3–7.4 × 0.6–1.8 cm, base truncate to truncate-auriculate or auriculate, occasionally overlapping rachis, acroscopic lobe deltate to acute, margins serrulate, apex acute to deltate;

costae adaxially glabrous.

x

= 41.

Nephrolepis exaltata

Nephrolepis

Habitat Terrestrial or epiphytic in forested to open habitats, most often as an epiphyte
Elevation 0 m (0 ft)
Distribution
from FNA
FL; West Indies; Pacific Islands in scattered locations
[WildflowerSearch map]
[BONAP county map]
from USDA
Widespread in tropical areas
[BONAP county map]
Discussion

Nephrolepis exaltata is occasionally found farther north in the flora, but only as an escape from cultivation. Nephrolepis exaltata is usually confused with N. cordifolia when sterile; the latter species can be distinguished by its distinctly bicolored, adaxial rachis scales. These bicolored scales will distinguish N. cordifolia from all of the other species, even in the absence of other key features.

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

Nephrolepis often has veins ending in hydathodes and whitish lime-dots adaxially.

Cultivars of Nephrolepis occasionally are found in the wild, where they persist for some time. Numerous forms of N. exaltata cv. `Bostoniensis' and its derivatives are widely cultivated, and the following are known from Florida: N. exaltata cv. `Bostoniensis', N. exaltata cv. `Elegantissima' complex, N. exaltata cv. `Florida Ruffles', N. exaltata cv. `M. P. Mills'.

Nephrolepis falcata forma furcans (T. Moore in Nicholson) Proctor resembles N. biserrata in size, pinna shape, and sori, but it differs characteristically in having forking pinnae and rachises. It is widely cultivated and persists when escaped; it is not known to spread from spores. It is known in the literature under the following names: Aspidium biserratum Swartz var. furcans (T. Moore in Nicholson) Farwell, Nephrolepis biserrata (Swartz) Schott var. furcans (T. Moore in Nicholson) Hortus ex Bailey, and Nephrolepis davallioides var. furcans T. Moore in Nicholson.

Nephrolepis hirsutula (G. Forster) C. Presl cv. `Superba' has irregularly pinnatisect, elliptic pinnae and a dense covering of reddish orange scales over most of the leaf surfaces.

The report of Nephrolepis pectinata (Willdenow) Schott for Florida by E. T. Wherry (1964) was based on a misdetermination (T. Darling Jr. 1982).

Species 25–30 (4 in the flora).

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

Key
1. Adaxial costae of central pinnae sparsely to densely covered with short, erect hairs (often also with scales).
→ 2
1. Adaxial costae of central pinnae glabrous, with or without scales.
→ 4
2. Mature petioles at base covered moderately to densely with appressed, dark brown scales with pale margins.
N. multiflora
2. Mature petioles at base often with a few loose, reddish to light brown, concolored scales.
→ 3
3. Adaxial costae sparsely hairy, hairs ca. 0.5 mm; pinnae mostly falcate.
N. ×averyi
3. Adaxial costae densely hairy to tomentose, hairs 0.2-0.4 mm; pinnae not falcate or only slightly so.
N. biserrata
4. Indusia circular and peltate or horseshoe-shaped and attached at narrow sinus, largest ca. 1 mm wide; pinnae usually more than 5 cm, often with conspicuous hairs 0.3-0.4 mm on blade surface.
N. biserrata
4. Indusia reniform, horseshoe-shaped, or lunate to deltate-rounded and attached by narrow to broad sinus, 1.1-1.7 mm wide or wider; pinnae usually less than 5 cm, without hairs or hairs less than 0.3 mm and inconspicuous.
→ 5
5. Plants with or without tubers; adaxial rachis scales distinctly bicolored (pale with darker point of attachment), often dense; points of pinna attachment 5-12 mm apart; pinnae glabrous; indusia lunate to deltate-rounded or reniform.
N. cordifolia
5. Plants never bearing tubers; adaxial rachis scales concolored or indistinctly bicolored, dense to sparse; points of pinna attachment 7-21 mm apart; pinnae with a few scales near costae; indusia usually reniform to horseshoe-shaped.
N. exaltata
Source FNA vol. 2. FNA vol. 2.
Parent taxa Dryopteridaceae > Nephrolepis Dryopteridaceae
Sibling taxa
N. biserrata, N. cordifolia, N. multiflora, N. ×averyi
Subordinate taxa
N. biserrata, N. cordifolia, N. exaltata, N. multiflora, N. ×averyi
Synonyms Polypodium exaltatum
Name authority (Linnaeus) Schott: Gen. Fil. plate 3. (1834) Schott: Gen. Fil. plate 3. (1834)
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