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18. Nephrolepis Schott, Gen. Fil. plate 3. 1834.

Boston fern [Greek nephros, kidney, and lepis, scale, in reference to shape of the indusia]

Clifton E. Nauman

Plants terrestrial, epiphytic, or on rock. Stems ascending to erect, bearing wiry stolons and sometimes underground tubers. Leaves monomorphic, evergreen. Petiole 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 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. 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. x = 41.

Species 25--30 (4 in the flora): widespread in tropical areas.

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).


Darling, T. Jr. 1982. The deletion of Nephrolepis pectinata from the flora of Florida. Amer. Fern J. 72: 63. Nauman, C. E. 1981. The genus Nephrolepis in Florida. Amer. Fern J. 71: 35--40. Nauman, C. E. 1985. A Systematic Revision of the Neotropical Species of Nephrolepis Schott. Ph.D. dissertation. University of Tennessee. Wherry, E. T. 1964. The Southern Fern Guide. Garden City, N.Y.

1 Adaxial costae of central pinnae sparsely to densely covered with short, erect hairs (often also with scales).   (2)
+ Adaxial costae of central pinnae glabrous, with or without scales.   (4)
2 (1) Mature petioles at base covered moderately to densely with appressed, dark brown scales with pale margins.   1 Nephrolepis multiflora
+ Mature petioles at base often with a few loose, reddish to light brown, concolored scales.   (3)
3 (2) Adaxial costae sparsely hairy, hairs ca. 0.5 mm; pinnae mostly falcate.   2 Nephrolepis ×averyi
+ Adaxial costae densely hairy to tomentose, hairs 0.2-0.4 mm; pinnae not falcate or only slightly so.   3 Nephrolepis biserrata
4 (1) 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. .   3 Nephrolepis biserrata
+ 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 (4) 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.   4 Nephrolepis cordifolia
+ 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.   5 Nephrolepis exaltata

Lower Taxa


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