Asplenium adiantum-nigrum
Asplenium septentrionale
black spleenwort
fork spleenwort, northern spleenwort
not proliferous.
not proliferous.
ascending or short-creeping, infrequently branched;
scales dark brown to blackish throughout, narrowly deltate, 2–4(–5) × 0.2–0.5 mm, margins entire or shallowly denticulate to serrulate.
erect, much branched to produce dense many-stemmed tufts or mats bearing numerous crowded leaves;
scales dark reddish brown to black throughout, narrowly deltate, 2–4 × 0.3–0.6 mm, margins entire.
monomorphic.
monomorphic.
dark reddish brown proximally, often fading to green distally, lustrous, 2–20 cm, 2/3–2 times length of blade;
indument of black filiform scales and minute hairs.
dark reddish brown proximally, fading to green distally, 2–13 cm, 2–5 times length of blade;
indument absent.
deltate, 2–3-pinnate, 2.5–10 × 2–6.5 cm, thick, hairs dark, scattered, minute;
base truncate;
apex acute to acuminate, not rooting.
linear, simple or more often 1-pinnate, 0.5–4 × 0.1–0.4 cm, occasionally wider when pinnae strongly diverge, leathery, glabrous;
base acute;
apex acute, not rooting at tip.
in 4–10 pairs, deltate to lanceolate;
most proximal (largest) pinnae 1.5–4 × 1–2.5 cm;
base obliquely obtuse;
segment margins coarsely incised;
apex acute.
of pinnate leaves 2(–4), strongly ascending to give forked appearance, linear, (5–)10–30 × 0.75–3 mm;
base acute;
margins remotely lacerate;
apex acute.
free, evident.
free, obscure.
1–numerous pairs per pinna [1–6 pairs per segment], on both basiscopic and acroscopic sides.
usually 2+ per pinna, parallel to margins.
64 per sporangium.
64 per sporangium.
greenish throughout or sometimes reddish brown proximally, lustrous, sparsely pubescent.
green, lustrous, glabrous.
= 144.
= 144.
Asplenium adiantum-nigrum
Asplenium septentrionale
Asplenium adiantum-nigrum is principally a Eurasian species and occurs extremely rarely in North America (see M. G. Shivas 1969 and M. D. Windham 1983 for a discussion of the conspecificity of Western Hemisphere and Eastern Hemisphere material). It is an allotetraploid derived from hybridization of two European taxa, A. cuneifolium Viviani and A. onopteris Linnaeus (M. G. Shivas 1969). Hybrids involving A. adiantum-nigrum and other Asplenium species occur in Europe but are unknown in North America.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
In North America Asplenium septentrionale is principally a western species with isolated disjunct populations in Monroe and Hardy counties, West Virginia. Because of its close resemblance to a tuft of grass, it is easily overlooked, and discoveries of additional localities are to be expected. In Europe A. septentrionale is known to hybridize with several species, but in North America only the hybrid with A. trichomanes (A. × alternifolium Wulfen) is known.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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