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.