core Notholaena

Introduction

Core Notholaena are comprised of approximately 27 species of small, farinose ferns (see below) of New World xeric habitats, with their center of richness in Mexico. As such, it contains the vast majority of Notholaena sensu Windham (1993a) and Mickel and Smith (2004) and Chrysochosma sensu Pichi Sermolli (1989). The sole known exception is Notholaena standleyi, which falls outside the core Notholaena clade based on recent DNA evidence (Rothfels et al., 2008). This circumscription also differs substantially from that of Tryon (1956)—many of the taxa included in his treatment are now known to be pellaeids, myriopterids, or hemionitids. For a more complete list of taxa previously included in Notholaena, see notholaenids: Excluded Species.

The genus Notholaena suffers from some unfortunate nomenclatural confusion: the genus was lectotypified three different times, and two of those lectotypifications (N. trichomanoides and N. marantae) are still in active use. Unfortunately, N. trichomanoides and N. marantae are only distantly related (N. trichomanoides is here, in core Notholaena, whereas N. marantae is in the pellaeids), and so the choice of one lectotype over the other results in a dramatically different concept of the genus. I here follow the first lectotypification (N. trichomanoides), based primarily on the arguments presented by Yatskievych and Smith (2003) and Rothfels et al. (2008), and treat N. marantae under Paragymnopteris.

Characteristics

Left: Notholaena californica ssp. leucophylla. Note the farina-covered leaf under-surfaces exposed when the leaves roll inwards under water stress. Note also the black marginal sporangia, and the absence of a false indusium. Right: Notholaena aschenborniana. The farina characteristic of all members of the core Notholaena are present in this species, too, but hidden under a dense layer of scales. Images © 2008 Carl Rothfels

This clade contains nearly half of all the world’s known farinose fern species. This farina can be brightly colored (usually white, but also cream, yellow, or orange) and is believed to be an adaptation to help reduce water loss from the leaves. Indeed, when these plants are water stressed, they roll their leaves inwards, exposing the farina-covered undersides to solar irradiation, even though the leaf undersurfaces are where the stomata are located (Hevly, 1963). All members of core Notholaena are farinose, even those, like N. aschenborniana, that have their farina covered by a dense layer of hairs or scales (the exception that proves the rule are the disjunct Chiapas populations of N. rigida, which are apparently nonfarinose; Mickel and Smith, 2004). Outside of the notholaenids the presence of farina is unusual, and it is unknown outside of the Pteridaceae (see A Quick Guide to Farinose Ferns for a brief overview of the genera of farinose ferns).

From other farinose species, core Notholaena taxa can generally be recognized by the position of their sporangia (confined to vein-ends near the leaf margins) and by the absence of a recurved leaf margin protecting the sporangia (although a weakly differentiated margin is present in some species). Confusion is most likely with members of Argyrochosma (the False Cloakferns) and with Notholaena standleyi (Northern Desert Star Cloakfern). Notholaena standleyi has a unique leaf shape and dissection (but see N. sulphurea). The farinose species of Argyrochosma differ from the highly dissected Notholaena species (e.g., N. greggii) in the following characters: the sporangia extend somewhat along the veins (vs. confined to the vein tips); rhizome scales are uniformly tan or brown (vs. rhizome scales uniformly dark or bicolored with dark central stripe); and glabrous gametophytes (vs. farinose).

Discussion of Phylogenetic Relationships

Based on plastid DNA sequence data (Rothfels et al., 2008), core Notholaena species are divided into two well-supported clades: core Notholaena I and core Notholaena II. Core Notholaena I species tend to have linear-lanceolate leaves and are often hairy or scaly, whereas the species in core Notholaena II tend to have pentagonal leaves (or, at least, enlarged basioscopic pinnules on their basal pinnae), and are usually glabrous (Rothfels et al., 2008).

Other Names for core Notholaena

• Vernacular Names: Cloakferns

References

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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.

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