Asplenium adiantum-nigrum
Asplenium ebenoides
black spleenwort
Scott's 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.
ascending to erect, rarely branched;
scales dark brown to blackish throughout, narrowly deltate, 2–4 × 0.25–0.45 mm, margins entire.
monomorphic.
weakly subdimorphic, fertile leaves taller and more erect than sterile leaves.
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.
reddish or purplish brown throughout, lustrous, 1–10 cm, 1/5–1 times length of blade;
indument of dark brown to black scales, narrowly deltate at very base, grading into hairs distally.
deltate, 2–3-pinnate, 2.5–10 × 2–6.5 cm, thick, hairs dark, scattered, minute;
base truncate;
apex acute to acuminate, not rooting.
highly variable and typically irregularly shaped, narrowly deltate to lanceolate, pinnatifid or 1-pinnate in proximal 1/3, 2–20 × 1–6(–13) cm, medium thick, sparsely pubescent adaxially only;
base ± truncate;
apex acute to long-attenuate, apical buds borne occasionally but not known to root in nature.
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.
in 0–3 pairs, often irregular in size and shape, deltate to narrowly deltate;
proximal pinnae 5–30(–80) × 3–10(–15) mm;
base truncate to obtuse, auriculate on both sides;
margins entire to finely serrate or crenulate;
apex obtuse to acute or occasionally attenuate.
free, evident.
somewhat evident, mostly free, rarely anastomosing.
1–numerous pairs per pinna [1–6 pairs per segment], on both basiscopic and acroscopic sides.
1–10(–15+) pairs per pinna, on both acroscopic and basiscopic lobes.
64 per sporangium.
malformed (sterile form) or 64 per sporangium (fertile form).
greenish throughout or sometimes reddish brown proximally, lustrous, sparsely pubescent.
reddish or purplish brown abaxially, fading to green distally, lustrous, glabrous.
= 144.
= 72, 144.
Asplenium adiantum-nigrum
Asplenium ebenoides
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.)
The above description applies to the sterile hybrid Asplenium platyneuron × rhizophyllum and its allopolyploid derivative. The allotetraploid form is known only from Hale County, Alabama, where it occurs with A. platyneuron (but not with A. rhizophyllum) on conglomerate boulders (K. S. Walter et al. 1982). The sterile diploid form of A. ebenoides occurs at elevations of 70 to 500 m within the region where the ranges of the parental species overlap, always occurring with both parents on limestone, sandstone, or other rock strata. A hybrid between the allopolyploid and A. platyneuron [A. × boydstoniae (K. S. Walter) J. W. Short] was discovered at Havana Glen. An unnamed hybrid between the sterile diploid (presumably via unreduced spores) and A. rhizophyllum is known from West Virginia and Missouri (K. S. Walter et al. 1982).
This fern has been pivotal in the study of fern hybridization. Called the "most famous hybrid fern," it was one of the first crosses to be synthesized deliberately in culture (M. Slosson 1902) and the first to be converted from the sterile diploid state to the fertile tetraploid state experimentally (W. H. Wagner Jr. and R. S. Whitmire 1957).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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