Formal recognition of six subordinate taxa within the South American bracken fern, Pteridium esculentum (P. esculentum subsp. arachnoideum s.l.—Dennstaedtiaceae), based on morphology and geography

Abstract

Based on the morphological study of ca. 470 specimens and geographical studies, we here propose the recognition of six morphotypes within the South American Pteridium esculentum (= P. arachnoideum s.l., or P. aquilinum var. arachnoideum sensu Tryon, or P. esculentum subsp. arachnoideum sensu Thomson). Three of them are widely distributed and well-defined, and we regard them as subspecies of P. esculentum: P. esculentum subsp. arachnoideum s. str., P. esculentum subsp. campestre, comb. et stat. nov., and P. esculentum subsp. gryphus. The other three are more rare. One of these is a pedomorphic form of P. esculentum subsp. arachnoideum, which we name as P. esculentum subsp. arachnoideum var. paedomorficum, nom. nov. The other is a glabrous form of P. esculentum subsp. gryphus, which we name P. esculentum subsp. gryphus var. harpianum, var. nov. The third is a putative hybrid between P. esculentum subsp. arachnoideum and P. esculentum subsp. campestre. All six taxa are keyed, described, illustrated, mapped, and discussed. Pteridium esculentum subsp. arachnoideum s. str. forms an arc of distribution from eastern, to southern, to western South America (but not occurring west of the Andes); Pteridium esculentum subsp. campestre forms an arc of distribution from northeastern Brazil to northern South America (not occurring west of the Andes either); and P. esculentum subsp. gryphus forms an arc of distribution from western to northern South America (occurring also west of the Andes and in Galapagos). This one is morphologically more similar to the Australasian P. esculentum subsp. esculentum.

Worldwide relationships in the fern genus Pteridium (bracken) based on nuclear genome markers

“…In contrast to the genetic subdivisions observed in Pteridium aquilinum , we detected no clear differences between Australian and South American P. esculentum . This finding is more consistent with the treatment as a single species (Thomson, ; Zhou et al., ; Schwartsburd et al., ) rather than as separate taxa with P. esculentum in Australia and P. arachnoideum in South America (see e.g., Schwartsburd et al., ).…”

“…We sampled Pteridium from most named taxa (Fig. , Appendix 1) except for some recently described forms of P. esculentum from South and Central America (Schwartsburd et al., ). We used 101 samples for ddRADseq and 96 for amplicon analysis.…”

“…The majority of brackens are diploid (2n = 104: summarized by Page, ; Marrs and Watt, ). Current treatments have converged to recognize two diploid species (Thomson, ; Zhou et al., ; Wolf et al., ; Schwartsburd et al., ). Pteridium aquilinum (L.) Kuhn is predominant in the northern hemisphere whereas P. esculentum (G.…”

“…In Pteridium , the problem is exacerbated by inconsistencies in morphological variation and what appears to be phenotypic plasticity for many traits (Page, ). In P. aquilinum (Boodle, ; Bright, ; Tryon, ) and in P. esculentum (O'Brien, ; Schwartsburd et al., , ), environmentally labile characters include features regarded as critical for taxonomic assignment, as well as occasional paedomorphy in the latter species. Furthermore, because of uncertainties in taxonomic delimitations, and because fern spores are so mobile, it is not unexpected to find intermediate phenotypes and apparent hybrids.…”

Weedy ferns (Polypodiopsida) in Argentina: diversity, distribution and impact on human activities and ecosystems

“…Lellinger (Lellinger 2003) y Pteridium psittacinum Maxon (Ramos Giacosa et al 2004). In the present work, we follow Thomson (2012) and Schwartsburd et al (2018).…”