Asplenium platyneuron

Asplenium platyneuron (L.) Britton, Sterns, & Poggenb.
(Greek: platys, broad, wide, or flat, and neuron, nerve, = broad-nerved, the name given by Linnaeus based on an inaccurate early drawing—Fernald 1950a; Thieret 1980; Nelson 2000)

Local names: ebony spleenwort, brown-stem spleenwort, Indian-hair fern

Rhizomes typically short-creeping, not branched; leaves slightly dimorphic, to 50 cm tall; leaf blades linear-lanceolate to narrowly elliptic-lanceolate or linear-oblanceolate in outline; petiole and rachis usually reddish brown to dark brown (rarely nearly black), shiny; pinnae usually alternate and oblong, usually crenate to serrate, sometimes prominently so to incised, usually with conspicuous acroscopic basal auricle which overlaps the rachis; 2n = 72 (Wagner et al. 1993). Sandy, moist, wooded banks and slopes, terrestrial or on rocks (it is the only TX species often seen growing terrestrially rather than on rock); widespread in the e 1⁄3 of TX w to Parker Co. (J. Quayle & O’Kennon 537, BRIT) in the West Cross Timbers; se Canada and throughout e U.S. w to NE, KS, OK, and TX and disjunct to isolated areas in AZ, e CO, and e NM; also disjunct to s Africa. Sporulating Apr–Dec. [A. platyneuron var. bacculum-rubrum (Fernald) Fernald, A. platyneuron var. incisum (Howe ex Peck) B.L. Rob.] Varieties are sometimes recognized in this species (e.g., Taylor et al. 1976; Kartesz 1999). However, due to the lack of consistent variation, we are following Wagner and Johnson (1983), Wagner et al. (1993), and Yatskievych (1999) in not recognizing infraspecific taxa. This is a generalist species and is according to Correll (1956), “… one of the commonest woodland ferns occurring in eastern Texas. It may be found not only as a solitary plant but also in extensive stands.” Wagner et al. (1993) noted that this species “… is remarkable in that it occurs in southern Africa as well as in North America. No other North American fern has this distribution.” This disjunct distribution (a distance across the Atlantic Ocean of approximately 12,000 km or roughly7,500 mi) is almost certainly the result of the long-distance dispersal by spores (Moran & Smith 2001; Moran 2008). Perhaps not surprisingly, Peck et al. (1990) found that this species is “well equipped” for long distance dispersal (e.g., self-fertile gametophytes, low levels of genetic problems). The species is also unusual in possessing trophopods; these modified petiole bases accumulate food reserves and persist after the leaf blade has withered (Wagner & Johnson 1981, 1983; Nauman et al. 2000). Wagner et al. (1993) pointed out that “proliferous buds on the lowest pinnae allow formation of clumps with stems at several layers in the litter.” Correll (1956) also noted that if grown in the sun under poor nutrient conditions, the plants are dwarfed, yellowish green, and have nearly entire or only slightly toothed pinnae. In the e U.S. A. platyneuron hybridizes with a number of other Asplenium species and is involved in a reticulate hybrid complex involving polyploidy (Wagner 1954).

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