Nephrolepis
Nephrolepis biserrata
Boston fern, swordfern
giant sword fern
ascending to erect, bearing wiry stolons and sometimes underground tubers.
scales loosely appressed to spreading, concolored or bicolored with pale margins.
monomorphic, evergreen.
2–22 × 0.3–3.5 dm.
ca. 1/10–1/2 length of blade, base not swollen;
vascular bundles more than 3, arranged in an arc, ± round in cross section.
0.2–5.4 dm, sparsely to moderately scaly;
scales spreading, reddish to light brown throughout (rarely with pale margins).
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.
sparsely to densely scaly, glabrous or pubescent, hairs mostly on veins and abaxial, pale to light brown, 0.2–0.7 mm.
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.
free, forked.
circular to horseshoe-shaped, peltate or attached at narrow sinus, 0.8–1.1 mm wide.
± round;
indusia round-reniform and with deep sinus to semicircular with broad sinus or lunate without sinus and seemingly laterally attached, persistent.
brownish, tuberculate to rugose.
absent.
1.8–17 dm, points of pinna attachment 7.5–35 mm apart;
scales moderately spaced, pale brown throughout.
pinnae narrowly deltate to narrowly elliptic-lanceolate, 2.5–23 × 0.5–2 cm, base cuneate, truncate to auriculate-cordate acroscopically, rounded basiscopically, acroscopic lobe small and oblong or absent, margins biserrate to serrulate, apex attenuate;
costae adaxially glabrous or densely hairy, hairs erect, pale, 0.3 mm.
= 41.
= 82.
Nephrolepis
Nephrolepis biserrata
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.)
Some forms of Nephrolepis biserrata closely resemble N. multiflora in pinna shape and indument but lack the distinctively transparent-margined (i.e., bicolored) and persistent petiole scales of the latter species. Nephrolepis multiflora also has more appressed and darker-colored stem scales.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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 |
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