Cheiloplecton rigidum (Sw.) Fée 1857

Introduction

Cheiloplecton rigidum is an enigmatic species of Mexico and northern Central America. It is found in both mesic and dry habitats, often in wooded areas, and often on rocky slopes. It has been a taxonomic challenge—it is often placed in either Cheilanthes or Pellaea—and has only recently (Rothfels et al., 2008) been shown to be embedded within Notholaena s. s. (Notholaena sensu Mickel and Smith, 2004; Windham, 1993a).

Currently, two varieties are recognized within Cheiloplecton rigidum (following Mickel and Smith, 2004): Cheiloplecton rigidum var. rigidum and C. rigidum var. lanceolatum C.C. Hall ex Mickel & Beitel. The two differ in leaf shape and characteristics of their rhizome scales, and both are triploids. However, the presence of intermediates (Mickel and Smith, 2004) and probable diploid populations (Windham and Rothfels, unpublished data) suggest that the relationships within Cheiloplecton may be more complex than generally recognized.

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Above: An example of a plant that appears to be intermediate between the two varieties: It has slightly enlarged basal basioscopic pinnules on the basal pinnae, but is only very weakly delate, and has a longer leaf blade than expected for var. rigidum. Image © 2009 Carl Rothfels.

Characteristics

With its thick, nonfarinose leaf blades, Cheiloplecton superficially resembles some of the species of Pellaea (in the pellaeids) that have less-divided leaves, or species of Doryopteris (in the hemionitids). But that resemblance is, indeed, superficial. Cheiloplecton has a different leaf dissection (pinnate-pinnatifid to barely 2-pinnate on the lowest pinnae), and most strikingly, a unique fertile leaf margin. This margin is doubly recurved, such that it nearly forms a tube protecting the sporangia. For young plants, especially, the most likely confusion is between Cheiloplecton and Mildella intramarginalis (in the hemionitids). Mildella, however, has a “false margin” that protrudes from the junction of the leaf blade and the false indusium, and is generally glabrous except for short club-shaped hairs on the side of the leaf stalk.

In retrospect, Cheiloplecton does resemble a few other notholaenids, particularly Notholaena ochracea. In silhouette N. ochracea very closely resembles Cheiloplecton rigidum var. lanceolatum. However, the former is farinose (bright orange farina), and lacks the distinctive false indusium of Cheiloplecton.

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Above: The underside of a Cheiloplecton leaf, showing the prominent inrolled false indusia, protecting the sporangia. Image © 2009

Other Names for Cheiloplecton rigidum (Sw.) Fée 1857

• Pteris rigida Sw. 1806
• Pellaea rigida (Sw.) Hook. 1858
• Cheilanthes rigida (Sw.)Mett. 1859
• Pteris cartilaginea C.Presl 1825
• Cheiloplecton

References

Gastony, G. J., and D. R. Rollo. 1995. Phylogeny and generic circumscriptions of cheilanthoid ferns (Pteridaceae: Cheilanthoideae) inferred from rbcL nucleotide sequences. American Fern Journal 85:341-360.

Gastony, G. J., and D. R. Rollo. 1998. Cheilanthoid ferns (Pteridaceae: Cheilanthoideae) in the southwestern United States and adjacent Mexico--A molecular phylogenetic reassessment of generic lines. Aliso 17:131-144.

Mickel, J. T., and A. R. Smith. 2004. The Pteridophytes of Mexico. The New York Botanical Garden Press, New York.

Rothfels, C. J., M. D. Windham, A. L. Grusz, G. J. Gastony, and K. M. Pryer. 2008. Toward a monophyletic Notholaena (Pteridaceae): Resolving patterns of evolutionary convergence in xeric-adapted ferns Taxon 57:712-724.

Tryon, R. M. 1956. A revision of the American species of Notholaena. Contributions from the Gray Herbarium 179:1-106.

Windham, M. D., L. Huiet, E. Schuettpelz, C. J. Rothfels, J. Beck, A. L. Grusz, G. Yatskievych, and K. M. Pryer. 2008. Using plastid and nuclear DNA sequences to redraw generic boundaries and demystify species complexes in cheilanthoid ferns. American Fern Journal (in review).