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Mason Campbell
Mason Campbell

Asplenium Pinnatifidum WORK

Lobed spleenwort Asplenosorus pinnatifidus (Nuttall) MickelRoots not proliferous. Stems short-creeping to erect, frequently branched; scales dark reddish brown, narrowly deltate, 3--5 0.3--0.5 mm, margins entire. Leaves monomorphic. Petiole dark reddish brown at base, fading to green in distal 1/3--1/2, lustrous, 1--10 cm, 1/5--1 times length of blade; indument of dark reddish brown, narrowly deltate scales at very base, grading distally into hairs. Blade narrowly deltate, often irregular in outline, pinnatifid or often with single pair of pinnae proximally, 2--17(--20) 1--4(--13) cm, thick, pubescent abaxially only; base truncate, cordate, or auriculate; apex acute to long-attenuate, proliferous bud very rare, not known to root in nature. Rachis green, sometimes drying to tan, dull; hairs on abaxial surface only, scattered, minute. Pinnae 0--1 pair, ovate to deltate, sometimes narrowly so, 5--20(--90) 0.4--1(--1.2) mm; base truncate to acute; margins crenate to serrate; apex rounded to attenuate. Veins free (rarely anastomosing), obscure. Sori 1--6(--40+) per segment, usually confluent with age. Spores 64 per sporangium. 2 n = 144.Cliffs, ledges, and boulders of sandstone and other acidic rocks; 0--1000 m; Ala., Ark., D.C., Ga., Ill., Ind., Ky., Md., Miss., Mo., N.J., N.C., Ohio, Okla., Pa., S.C., Tenn., Va., W.Va., Wis.Asplenium pinnatifidum is an allotetraploid derived from the hybrid A . montanum rhizophyllum . Although isozyme studies indicate that this species originated at more than one site (C. R. Werth et al. 1985b), the sterile diploid hybrid is unknown. The species is uncommon in the eastern part of the Appalachian region and becomes much more frequent in the Cumberland and Interior Low plateaus, extending westward into the Ozarks and Ouachitas. It is disjunct in the Driftless Area of Wisconsin in Iowa County (M. G. and R. P. Hanson 1979). It crosses frequently with A . montanum (producing A . trudellii Wherry), with A . bradleyi (producing A . gravesii Maxon), with A . platyneuron (producing A . kentuckiense McCoy), and with A . trichomanes (producing A . herb-wagneri W. C. Taylor & Mohlenbrock).

asplenium pinnatifidum


Asplenium pinnatifidum, commonly known as the lobed spleenwort or pinnatifid spleenwort, is a small fern found principally in the Appalachian Mountains and the Shawnee Hills, growing in rock crevices in moderately acid to subacid strata. Originally identified as a variety of walking fern (Asplenium rhizophyllum), it was classified as a separate species by Thomas Nuttall in 1818. It is believed to have originated by chromosome doubling in a hybrid between walking fern and mountain spleenwort (Asplenium montanum), producing a fertile tetraploid, a phenomenon known as alloploidy; however, the hypothesized parental hybrid has never been located. It is intermediate in morphology between the parent species: while its leaf blades are long and tapering like that of walking fern, the influence of mountain spleenwort means that the blades are lobed, rather than whole. A. pinnatifidum can itself form sterile hybrids with several other spleenworts.

Asplenium pinnatifidum is a small fern with bright green, wrinkled, pinnatifid (lobed) fronds.[2][3] These form evergreen, perennial tufts.[3] Notable characteristics are the shiny stem, dark only at the base, and the long-tapering, variably lobed leaf blades.[2] The fronds are monomorphic, the sterile and fertile fronds appearing the same size and shape.[3]

The roots of A. pinnatifidum are not proliferous, so it appears as clusters of leaves springing from a single rhizome. The leaves are closely spaced on the rhizome, which is frequently branched.[2] The rhizome is about 1 millimeter (0.04 in) in diameter, covered with narrowly triangular scales which are dark reddish-brown or blackish in color, and strongly clathrate (bearing a lattice-like pattern).[2][4] The scales are 3 to 5 millimeters (0.1 to 0.2 in) long and 0.3 to 0.5 millimeters wide, with untoothed edges. The stipe (the stalk of the leaf, below the blade) is shiny and dark reddish brown at the base. The color fades to green in the upper one-third to one-half of the stipe. It is covered in narrowly triangular, dark reddish-brown scales at the base, which diminish into hairs in the upper part of the stipe.[2] It may show narrow wings from the base of the leaf to near the base of the stipe.[4] The stipe is 1 to 10 centimeters (0.4 to 4 in) long,[2] and may be from one-tenth to one and one-half times the length of the blade.[3]

While no named varieties or forms of A. pinnatifidum have been described, an unusual population was described from Giant City State Park in southern Illinois in 1956. In it, the leaf blade was highly reduced, barely exceeding the rachis, except for a series of stubby projections under which the sori were borne.[7] Individual plants have also been known on occasion to develop forked leaves, which appears to be a developmental accident rather than a stable genetically-controlled trait.[8]

A. pinnatifidum is somewhat similar to its parent species A. rhizophyllum. In comparison, however, A. pinnatifidum is distinctly lobed when mature, tends to have longer stipes in proportion to its leaf size, and has a more upright habit.[3] It might be confused with Countess Dalhousie's spleenwort (A. dalhousiae), of Asia and the American Southeast, but the latter has short, dull stipes with larger, toothed scales.[2] A. pinnatifidum closely resembles the hybrid Scott's spleenwort (A. ebenoides) (including the fertile Tutwiler's spleenwort, A. tutwilerae), but those species have a wholly dark stipe, with the dark color extending into the rachis,[2][3] and longer lobes on the blade.[4]

Among the hybrid species of which it is a parent, A. pinnatifidum is most similar to Graves' spleenwort (A. gravesii), a hybrid with Bradley's spleenwort (A. bradleyi), and to a lesser extent, to Trudell's spleenwort (A. trudellii) and Kentucky spleenwort (A. kentuckiense). In A. gravesii, the dark color of the stipe extends to the base of the leaf blade, the blades often have more than one pair of pinnae, and their edges are shallowly wrinkled or toothed. In addition, the basal pinnae, which may themselves be pinnatifid, lack a stalk, the leaf blade is pointed at the tip but not drawn out at length, and there are generally fewer fronds. Its sori are dark brown, rather than cinnamon brown.[9] A. trudellii is fully pinnate in the lower half of the blade, and its pinnae are toothed.[10] A. kentuckiense is also fully pinnate towards the base of the blade, with four to six pairs of pinnae, and the brown color of its stipe extends up into the basal part of the rachis.[11]

Lobed spleenwort was first recognized by Henry Muhlenberg in 1813, who considered it a variety of Asplenium rhizophyllum, although he did not provide a description distinguishing the variety.[12] In 1818, Thomas Nuttall observed that it was always distinguishable from A. rhizophyllum, and described it as a species under the name of Asplenium pinnatifidum.[13] Alphonso Wood used the name Camptosorus pinnatifidus for the species in 1870,[14] but this was not widely accepted.

Oliver A. Farwell, observing an unusual specimen of A. pinnatifidum, was led to suggest that the species might be a hybrid between American walking fern, Camptosorus rhizophyllus (now A. rhizophyllum), and ebony spleenwort (A. platyneuron). Such a hybrid, Scott's spleenwort (A. ebenoides) was already known, but Farwell thought it bore a greater affinity to A. platyneuron while A. pinnatifidum had a greater affinity to A. rhizophyllum.[15] He was correct in viewing A. pinnatifidum as a hybrid descendant of A. rhizophyllum, but incorrect in identifying the other parent, and his suggestion was not widely taken up in the literature. Nor did his later attempt at subdividing Asplenium, moving A. pinnatifidum to a new genus as Chamaefilix pinnatifida in 1931,[16] meet with much favor.

As a member of the "Appalachian Asplenium complex", A. pinnatifidum readily acts as the progenitor of hybrids, as well. A. gravesii was recognized as a hybrid of A. pinnatifidum and A. bradleyi by W. R. Maxon in 1918.[9] Edgar T. Wherry noted the similarities between A. montanum, A. pinnatifidum, and A. trudellii in 1925,[10] and in 1936 concluded that Trudell's spleenwort was a hybrid between the first two.[17] That same year, A. kentuckiense was described by Thomas McCoy; Wherry identified it as a hybrid between A. pinnatifidum and A. platyneuron.[17] In 1951, Herb Wagner, while reviewing Irene Manton's Problems of Cytology and Evolution in the Pteridophyta, suggested in passing that A. pinnatifidum itself might represent a hybrid between A. montanum and A. rhizophyllum.[18]

In 1953, he made chromosome counts of A. trudellii, which had been classified by some simply as a variety of A. pinnatifidum. As A. pinnatifidum proved to be a tetraploid while A. montanum was a diploid, a hybrid between them would be a triploid, and Wagner showed that this was in fact the case for A. trudellii.[19] His further experiments, published the following year, strongly suggested that A. pinnatifidum is an allotetraploid, the product of hybridization between A. montanum and A. rhizophyllum to form a sterile diploid, followed by chromosome doubling that restored fertility.[20] However, the hypothesized sterile diploid has never been found.[2][a] Partial pairing of homologous chromosomes in A. gravesii and A. trudellii confirmed A. montanum parentage for A. pinnatifidum,[21] while an artificial hybrid between A. pinnatifidum and Tutwiler's spleenwort (A. tutwilerae) helped confirm their shared A. rhizophyllum parentage.[22] 041b061a72


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