Clarification of the taxonomic status and relationships of Pteridium caudatum (Dennstaedtiaceae) in Central and South America

Abstract

Contemporary systematic treatments of the Central and South American bracken ferns in the genus Pteridium Gled. ex Scop. recognize morphotype caudatum as either a full species or a variety of P. aquilinum (L.) Kuhn. Geographically representative sporophytes of morphotype caudatum, including the type in the Linnaean Herbarium, are shown using spore size, guard‐cell length and morphology of the cells of the false indusium to be tetraploid (based on 4n = 208). DNA fingerprinting of field‐collected Venezuelan samples supports the generalization that morphotype caudatum is a fertile allotetraploid containing genomic elements otherwise distinctive of the southern hemisphere diploid P. arachnoideum (Kaulf.) Maxon, together with elements characteristic of northern hemisphere diploids including the North American P. aquilinum var. pubescens Underw. and P. aquilinum var. pseudocaudatum (Clute) A. Heller. Evidence of genetic isolation from taxa with overlapping distributions, as well as morphological, biochemical and ecological data, validate recognition of P. caudatum (L.) Maxon at species level. Heterogeneity observed within P. caudatum is consistent with multiple origins through independent hybridization events. Pteridium caudatum is strikingly analogous to the tropical Asian/Australasian allotetraploid P. semihastatum (N. Wallich ex J. G. Agardh) S. B. Andrews [=P. yarrabense (Domin) N. A. Wakef.]. © 2002 The Linnean Society of London. Botanical Journal of the Linnean Society, 2002, 140, 237−248.

Palynological analysis of Dennstaedtiaceae taxa from the Paranaense Phytogeographic Province that produce Trilete spores II: Microlepia speluncae and Pteridium arachnoideum

“…As a consequence of its broad distribution, poorly stable diagnostic features, population phenotype plasticity, and the existence of intermediate morphotype, there are several views on the taxa classifi cation within Pteridium. While some authors describe it as a monotypic genus with several varieties (Tryon 1941, Cooper-Driver 1976, Van Cotthem 1970, Taylor 1990, others have acknowledged several species (Thomson and Alonso-Amelot 2002, Thomson 2004, Thomson et al 2005. In the present work we follow the classifi cation scheme used by Der et al (2009), based on phylogenetic and biogeographical studies.…”

Free Axial Lobes: An Important Diagnostic Character in Pteridium (Dennstaedtiaceae)

“…2014), as are many specimens of subsp. arachnoideum from Central and South America that have both free lobes and gnarled trichomes (Thomson 2000, Thomson and Alonso-Amelot 2002, Wolf et al 2015. The study by Schwartsburd et al (2014) was numerically large scale, established diploidy for a sample of the collections and revealed a coherent geographic distribution of sites for each morphotype.…”

“…ex J. Agardh) W.C. Shieh in South-East Asia/Australia while P. caudatum (L.) Maxon is an allotetraploid hybrid of P. esculentum subsp. arachnoideum with P. aquilinum (subspecies not identified) in Central and South America (Thomson and Alonso-Amelot 2002, Der et al 2009, Zhou et al 2014, Wolf et al 2015. There is evidence in both of these cases that hybrids or introgressants other than the allotetraploids are also present (Brownsey 1989, 1998, Wolf et al 2015, meriting additional cytological, molecular and morphological analysis.…”

“…ex Scop.) with a diploid (2n = 104) chromosome complement group on many morphological and molecular features into two distinct clades (Der et al 2009, Thomson 2012, Zhou et al 2014, Wolf et al 2015 between which there is evidence of reproductive incompatibility (Brownsey 1989, Thomson and Alonso-Amelot 2002, Thomson 2012. One of these clades comprises P. aquilinum (L.) Kuhn, predominantly from the northern hemisphere and Africa, considered to include 11 (Thomson 2004(Thomson , 2008(Thomson , 2012 or fewer (Zhou et al 2014) subspecies.…”

“…Tryon 1941, Mickel and Beitel 1988, Mickel and Smith 2004, Thomson 2012. One of these critical characters is the presence of minute highly distorted hairs termed gnarled trichomes (Thomson and Martin 1996, Thomson and Alonso-Amelot 2002, Schwartsburd et al 2014, Wolf et al 2015 between veins on the abaxial surface of laminal segments of P. esculentum s.l. If sufficiently dense, these hairs are seen at low magnifications as a surface texture that has been described as farinaceous (Tryon 1941, Schwartsburd et al 2014, mealy (Brownsey 1989), or farinose (Schwartsburd et al 2014).…”