Botrychium dissectum

Botrychium dissectum Spreng.
(Latin: dissectus, cut up, deeply divided, dissected)

Local names: cut-leaf grape fern, oblique grape fern, dissected grape fern

Plant extremely similar to B. biternatum; leaves present over winter, often bronze or reddish bronze in winter if exposed (but more so in colder areas of the n U.S.); new leaves appearing in late spring; sterile blade portion shiny green, relatively leathery, to 20 cm long and 30 cm wide, mostly 3-pinnate, the ultimate segments usually ± trowel-shaped (rarely linear), the margins usually not parallel, denticulate to coarsely denticulate, the marginal teeth coarser and less uniform than in B. biternatum; 2n = 90 (Wagner & Wagner 1993). In various habitats from open grassy areas to deep forests; Anderson, Bowie, Fannin (Diggs & S. Beach s.n., 1999), Leon (E.S. Nixon 18512), Titus, and Walker (all BRIT—identified by J. Peck) cos., Pineywoods w to Post Oak Savannah and Red River drainage; Hatch et al. (1990) also cited the Blackland Prairie; while the range map in Wagner and Wagner (1993) shows this species in TX only on the extreme e margin of the Pineywoods, it occurs considerably further w; se Canada and throughout e U.S. w to KS, MN, OK, and TX. Spores maturing in the fall. [B. dissectum var. obliquum (Muhl. ex Willd.) Clute, B. dissectum var. oblongifolium (Graves) Broun, B. obliquum Muhl. ex Willd., B. obliquum var. elongatum Gilbert & Haberer, Sceptridium dissectum (Spreng.) Lyon] If Botrychium is divided into segregate genera, as argued by Hauk et al. (2003), B. dissectum would be recognized in the genus Sceptridium. Barker and Hauke (2003) noted that this is the “most variable North American grapefern species.” One form (forma dissectum—northern entity occurring as close to TX as c AR—J. Peck, pers. comm.) has highly dissected and quite distinctive leaves. However, molecular studies (Barker & Hauke 2003) do not show the forms to be genetically distinct and thus do not support recognizing the forms as formal varieties or subspecies. The only form occurring in TX (forma obliquum, previously treated as a variety) closely resembles B. biternatum. Thomas (1980) indicated that the two species intergrade and that some individual specimens puzzle even experts. As a result, B. dissectum and B. biternatum have often been confused (particularly immature plants). According to Taylor (1984) “… there do not appear to be any stable characters which will always clearly distinguish these two taxa.” Nauman et al. (2000) lumped B. dissectum into B. biternatum saying, “they intergrade in Florida to such an extent that two species cannot be maintained.” However, according to W.H. Wagner Jr. (pers. comm.) and Wagner and Wagner (1993), B. dissectum has leaves that are more dissected and the ultimate segments usually trowel-shaped (rarely linear), apically more pointed, and with the margins more lacerate. Likewise, J. Peck (pers. comm.) indicates that two species are distinct and that mature (reproductive) plants can usually be distinguished without difficulty. We are therefore following W.H. Wagner, Jr. (pers. comm.), Wagner and Wagner (1993) and J. Peck (pers. comm.) in recognizing B. dissectum as a distinct species.

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