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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However, the presence of intermediates (Mickel and Smith, 2004) and probable diploid populations (Windham and Rothfels, unpublished data) suggest that the relationships within Cheiloplecton may be more complex than generally recognized.
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.