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Pellaea zygophylla, a new combination for a distinctive & well-known but neglected fern.

27 Mar 2021-bioRxiv (Cold Spring Harbor Laboratory)-
TL;DR: Pellaea ovata is a widespread species, sexual diploid in Texas & northeastern Mexico but an apogamous triploid species in northwestern Mexico, south to northern Argentina, & on Hispaniola as discussed by the authors.
Abstract: AO_SCPLOWBSTRACTC_SCPLOWPellaea ovata is a widespread species, sexual diploid in Texas & northeastern Mexico but an apogamous triploid in northwestern Mexico, south to northern Argentina, & on Hispaniola. The type belongs to the southern, apogamous triploid form. Although these two forms have been discussed repeatedly in the literature, morphological distinctions between them have been overlooked and they have not been recognized taxonomically. However, they are distinct. Pellaea ovata s.s. has puberulent rachides & costae; pinnae usually 2-pinnate with a well-defined main axis & pinnules borne singly; fertile pinnules ovate, cordate basally & rounded apically. The sexual diploid form has rachides & costae glabrous; pinnae pseudo-dichotomously branched & pinnules usually paired; fertile pinnules narrowly rounded-trapeziform, obliquely truncate to cordate basally & truncate apically. Riddell named the sexual diploid form Pteris zygophylla, from which I give it the new combination Pellaea zygophylla.

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Summary

  • The type belongs to the southern, apogamous triploid form.
  • Morphological distinctions between them have been overlooked and they have not been recognized taxonomically.
  • One form had glabrous rachides & almost dichotomous branching in the pinnae, the other puberulent rachides & pinnae more straightforwardly pinnate.
  • I began to suspect that these may be separate species, a suspicion that lingered in the back of my mind over the following years.
  • The rachides & cosate are less flexuous than in either form of Pellaea ovata and the pinnules are not paired.
  • Was not certified by peer review) is the author/funder.

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Journal ArticleDOI
TL;DR: Chromosome numbers have been widely used to evaluate the evolutionary pattern of chromosome number change and to estimate the base chromosome number of clades of interest and phylogenetic information was incorporated into the analyses, allowing researchers to infer transitions in chromosome numbers along branches of the tree.
Abstract: For nearly a century, biologists, and botanists in particular, have been interested in the determination and documentation of chromosome numbers for extant taxa (reviewed in Goldblatt & Lowry, 2011) as well as extinct ones (Laane & Hoiland, 1986; Masterson, 1994). These data have beenwidely used to evaluate the evolutionary pattern of chromosome number change and to estimate the base chromosome number of clades of interest. Chromosome numbers have also been extensively utilized as an important phylogenetic character in the context of cytotaxonomy (Chatterjee & Kumar Sharma, 1969; Schlarbaum & Tsuchiya, 1984; Guerra, 2012). Perhaps the most influential use of chromosome number data has been in the inference of major genomic events such aswhole genomeduplications (polyploidy), as well as changes in single chromosome numbers (e.g. dysploidy). Early researchers analyzed the distribution of chromosome numbers within a group of interest and employed various threshold techniques to estimate ploidy levels for the analyzed taxa (Stebbins, 1938; Grant, 1963; Goldblatt, 1980).More recently, phylogenetic information was incorporated into the analyses, allowing researchers to infer transitions in chromosome numbers along branches of the tree using either the maximum parsimony principle (Schultheis, 2001; Hansen et al., 2006; Ohi-Toma et al., 2006; Wood et al., 2009) or by using a probabilistic evolutionary model within the likelihood paradigm (Mayrose et al., 2010; Cusimano et al., 2012; Glick & Mayrose, 2014). Due to their significance and the relative ease by which chromosome numbers can be obtained, it is not surprising that chromosome number is the most extensively and consistently recorded cytological property in most plant families and genera (Guerra, 2008). These data have been documented along the years in an array of journal manuscripts, printed books (L€ove & L€ove, 1948; Darlington & Wylie, 1955; Fedorov, 1969) and, more recently, in the form of online databases (Goldblatt & Johnson, 1979; Watanabe, 2002; Bennett & Leitch, 2011). To date, the most comprehensive data source is the Index to PlantChromosome Numbers (IPCN; Goldblatt & Johnson, 1979), which provides reference point to original chromosome counts reported in the literature. IPCN was initially established at the University of California Berkeley in the 1950s and was later maintained by Canada Department of Agriculture, Missouri Botanical Garden, and currently by the International Association for Plant Taxonomy (IAPT). A large portion of the counts referenced during 1979– 2006, the years that IPCN has been housed in the Missouri Botanical Garden, can be accessed and searched online. Counts reported in more recent years are currently published under IAPT/ IOPBChromosomeData series (Marhold, 2006) but are not stored within a central, easily searched, database. In addition to IPCN, several other online data sources are available, most of which are dedicated to either a specific geographical region (Slovakia – Marhold et al., 2007; Poland –G oralski et al., 2009 onwards) or to a certain taxonomic group (e.g. Hieracium – Schuhwerk, 1996; Asteraceae –Watanabe, 2002). The amount of chromosome counts that exist to date is extensive, and searching the large number of resources that contain such information is a daunting task, particularly when a large number of taxa is examined. Consequently, many researchers search for chromosome number information only through the largest online database(s), while smaller but nonetheless valuable sources are ignored.This usually results inmissing data for someof the species in question, which may lead to erroneous conclusions drawn from the analysis. Obviously, a large accessible database that unifies all currently known databases, including both printed and online sources, would be of great value to the botanical community and wouldmake the task of data collectionmuch easier. In addition, such a central resource would enable researchers to add new counts as soon as they are being reported, facilitating the task of data sharing. Here, we present the Chromosome Counts Database (CCDB), as a community resource of plant chromosome numbers. The database incorporates data from dozens of sources, more than doubling the amount of data available within any single resource. The online database additionally enables researchers to add new counts or to comment on existing data entries, thereby facilitating data sharing. The extensive amount of data currently available in CCDB further allowed us to analyze the patterns of chromosome number distribution among major plant groups. We estimate the percentage of plant species exhibiting intraspecific variation in chromosome numbers as well as in their ploidy levels.

472 citations

Book
01 Aug 1969

367 citations

Journal ArticleDOI
TL;DR: The present investigation was undertaken as a cytological survey of a group of closely related species with particular reference to apogamy, when it was noted in a revision of Pellaea section Pellaea Tryon (1957) that the relationships of several entities in the group were complicated by Apogamy and apparently hybridization.
Abstract: Apogamy in ferns involving the premeiotic doubling of the chromosome number has recently been reported by Manton (1950) to occur in several unrelated species including Pellaea atropurpurea. A second report was made of apogamy in Pellaea, in a floristic survey of the chromosome numbers of ferns of eastern North America, by Britton (1953) in P. glabella var. glabella. The present investigation was undertaken as a cytological survey of a group of closely related species with particular reference to apogamy, when it was noted in a revision of Pellaea section Pellaea Tryon (1957) that the relationships of several entities in the group were complicated by apogamy and apparently hybridization. The genus Pellaea belongs to the tribe Cheilantheae of the Polypodiaceae and the fifteen species included in section Pellaea are predominately Cordilleran, growing in dry, rocky habitats, under semi-deAert conditions quite unlike that usually associated with ferns.

38 citations

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Q1. What have the authors contributed in "Pellaea zygophylla, a new combination for a distinctive & well- known but neglected fern" ?

I began to suspect that these may be separate species, a suspicion that lingered in the back of my mind over the following years. The Texas plants belonged to the glabrous, dichotomous form, and Texas plants were reported to be sexual & diploid ( Tryon 1957, Tryon & Britton 1958, Tryon 1968, Tryon 1972 ). The pubescent, pinnate form must correspond with the reported apomictic triploids, then. Recently, this taxonomic question regained my attention while reviewing observations on iNaturalist. In this paper I do so, provide morphological descriptions & distribution maps for this species along with Pellaea oaxacana and Pellaea ovata, and discuss some of the remaining uncertainties surrounding these species. This unpublished manuscript and its associated materials were sent to Gray Herbarium, where they now reside. Within this description, the following features are especially relevant: stipe & frond glabrous ; pinnules mostly in pairs, trapeziform, apex truncate. Was not certified by peer review ) is the author/funder. This article is a US Government work.