Phylogeny of Chinese Polystichum (Dryopteridaceae) based on chloroplast DNA sequence data (trnL-F and rps4-trnS)

Historical biogeography of the fern genus Polystichum (Dryopteridaceae) in Austral South America

A group of seven endemic Polystichum species inhabit Patagonia, the southern region of South America. To date, evolutionary relationships of these Austral South American Polystichum remain unknown. The biota of the Southern Andes appears to be more closely related to the temperate Australasian species than to northern South American ones. Differences in morphological characters suggested that Austral South American Polystichum follows that biogeographical pattern, not being closely related to their congeners in the Northern and Central Andes. We sought to reveal the evolutionary relationships, estimate the divergence times and reconstruct both ancestral areas and ancestral ploidy levels of Austral South America Polystichum. Phylogenetic relationships were estimated using maximum likelihood and Bayesian approaches. The seven Austral South American species plus 31 Polystichum species spanning all other major biogeographic regions were sampled for three DNA markers. Divergence times were estimated in BEAST and Bayesian binary Markov chain Monte Carlo reconstruction was applied in order to infer ancestral areas. The evolution of ploidy was reconstructed on the maximum clade credibility tree, using stochastic character mapping. Austral South American Polystichum was recovered as monophyletic. The earliest divergence reconstructed within the Austral South American Clade was that of Polystichum andinum; subsequently two other lineages diverged comprising the remaining Austral South American species. The Austral South American lineage is not closely allied to North and Central Andes congeners. Long-distance dispersal of an ancestral tetraploid from Australasia during the late Miocene is the most likely explanation for the origin of Patagonian Polystichum. Then, Pliocene and Pleistocene orogenic and climatic changes may have shaped its diversification in Patagonia.

A plastid phylogeny of the fern genus Arachniodes (Dryopteridaceae)

Arachniodes (Dryopteridaceae) is one of the most confusing and controversial fern genera in terms of its circumscription, nomenclature, and taxonomy. Estimates of species number range from 40 to 200. Previous molecular works included only 2-17 accessions representing 2-12 species of Arachniodes and allied genera, leaving most of the Asian species remain unsampled and the infragneric relationships unclear. In this study DNA sequences of seven plastid markers of 343 accessions representing ca. 68 species of Arachniodes (275 accessions), and 64 outgroup accessions from subfam. Dryopteridoideae and subfam. Polybotryoideae were used to infer a phylogeny with maximum likelihood, Bayesian inference, and maximum parsimony approaches. Our major results include: (1) Two species currently assigned in Arachniodes (A. macrostegia and A. ochropteroides are resolved outside of the core Arachniodes making the currently defined Arachniodes polyphyletic, confirming earlier findings; (2) Lithostegia, Leptorumohra, and Phanerophlebiopsis are indeed synonyms of Arachniodes; (3) Leptorumohra is confirmed to be monophyletic, but Phanerophlebiopsis is polyphyletic; (4) The New World species of Arachniodes are confirmed to be not monophyletic with A. denticulata being nested within the Old World species, suggesting that this species is dispersed from the Old World; (5) Arachniodes s.s is resolved into 12 major clades, some of which are further divisable into recognizable subclades and groups, with A. mutica from Japan being resolved as the sister to the rest of the genus; (6) A number of systematic implications of the phylogeny have been suggested; and (7) the genus is estimated to contain ca. 83 species.

A light and scanning electron microscopic diagnosis of leaf epidermal morphology and its systematic implications in Dryopteridaceae: Investigating 12 Pakistani taxa

Dryopteris and Polystichum are the 2 complex taxonomic genera of Dryopteridaceae. The comparative foliar epidermal anatomy of 12 species of both genera from Pakistan were studied using standard protocols of light microscopy (LM) and scanning electron microscopy (SEM). The objective of which was systematic comparison and investigation to elucidate the taxonomic importance of foliar micromorphology, which may be useful to taxonomists for identifying complex Dryopteridaceae taxa. Principal component analysis and UPGMA clustering analysis were performed to test the validity of leaf anatomical features as method of separating species and genera. The foliar epidermal anatomy described here is a good source of taxonomic characters in both groups that can help genera and species delimitation. This is the first report on leaf micromorphology in most of these species. Observation of foliar anatomy showed that stomata are only present on the abaxial surface; i.e., leaves of all species are hypostomatic. The shapes of epidermal cells in all studied species are irregular. The anticlinal walls are strongly lobed, irregular wavy and elongated wavy. However, substantial variation in epidermal cell size and other stomatal features were observed on both upper and lower surfaces in all investigated species. Two types of stomata were observed in all studied species. The presence of polocytic stomata in Dryopteris and staurocytic stomata in Polystichum are the important characters for the segregation of these genera. Elongate elliptic stomatal shape, narrow kidney shaped guard cells and broad elliptic shaped stomatal pores are diagnostic for all five species of Dryopteris selected. On the other hand, size and number of epidermal cells, lobes per cell, stomatal size, subsidiary cell size, stomatal pore size and stomatal index are the key features for species differentiation in Polystichum. An identification key was developed in order to apply the foliar anatomical characters in the discrimination of the species studied.

Using a multilocus phylogeny to test morphology-based classifications of Polystichum (Dryopteridaceae), one of the largest fern genera

BACKGROUND

Polystichum (Dryopteridaceae) is probably the third largest fern genus in the world and contains ca. 500 species. Species of Polystichum occur on all continents except Antarctica, but its highest diversity is found in East Asia, especially Southwest China and adjacent regions. Previous studies typically had sparse taxon sampling and used limited DNA sequence data. Consequently, the majority of morphological hypotheses/classifications have never been tested using molecular data.

RESULTS

In this study, DNA sequences of five plastid loci of 177 accessions representing ca. 140 species of Polystichum and 13 species of the closely related genera were used to infer a phylogeny using maximum likelihood, Bayesian inference, and maximum parsimony. Our analyses show that (1) Polystichum is monophyletic, this being supported by not only molecular data but also morphological features and distribution information; (2) Polystichum is resolved into two strongly supported monophyletic clades, corresponding to the two subgenera, P. subg. Polystichum and P. subg. Haplopolystichum; (3) Accessions of P. subg. Polystichum are resolved into three major clades: clade K (P. sect. Xiphophyllum), clade L (P. sect. Polystichum), and the HYMASO superclade dominated by accessions of P. sect. Hypopeltis, P. sect. Macropolystichum, and P. sect. Sorolepidium, while those of P. subg. Haplopolystichum are resolved into eight major clades; and (4) The monophyly of the Afra clade (weakly supported), the Australasian clade (weakly supported), and the North American clade (strongly supported) is confirmed.

CONCLUSIONS

Of the 23 sections of Polystichum recognized in a recent classification of the genus, four (P. sect. Hypopeltis, P. sect. Neopolystichum, P. sect. Sorolepidium, P. sect. Sphaenopolystichum) are resolved as non-monophyletic, 16 are recovered as monophyletic, and three are monospecific. Of the 16 monophyletic sections, two (P. sect. Adenolepia, P. sect. Cyrtogonellum) are weakly supported and 14 are strongly supported as monophyletic. The relationships of 11 sections (five in P. subg. Haplopolystichum; six in P. subg. Polystichum) are well resolved.

Phylogeny and biogeography of exindusiate Andean Polystichum (Dryopteridaceae)

PREMISE OF THE STUDY

Uplift of the tropical Andes had a significant impact on the diversification of South American flora and fauna. Recent biogeographic inquiries have established patterns of Andean divergence, but investigations on ferns are scant. The fern genus Polystichum Roth (Dryopteridaceae) combines widespread geographic and elevational distribution with a large number of species to form an ideal system for investigation of the origin and diversification patterns of a fern lineage in the tropical Andes.

METHODS

The relationships among 42 Polystichum species, including taxa from all major biogeographic regions, were analyzed with 2591 aligned nucleotides from four plastid markers using maximum parsimony and Bayesian inference. The resulting phylogeny was then used to estimate divergence times and reconstruct both ancestral areas and ancestral elevations.

KEY RESULTS

Tropical Andean South American polystichums that lack an indusium (sori exindusiate) were confirmed to form a monophyletic group. This exindusiate Andean Polystichum clade diverged from a middle-elevation forest lineage now rich in species endemic to Mexico during the middle Miocene (13.12 million years ago). The majority of diversification that followed took place in the montane regions of the central Andes with radiations to the northern Andes, southeastern Brazil, and alpine regions.

CONCLUSIONS

The monophyletic exindusiate Andean Polystichum lineage diverged from a Mexican lineage in the middle Miocene and diversified in the central Andes before dispersing northward. This south-to-north dispersal pattern, documented for many other Andean lineages, corresponds with episodes of uplift in the tropical Andes.

The Evolutionary Dynamics of Apomixis in Ferns: A Case Study from Polystichoid Ferns

The disparate distribution of apomixis between the major plant lineages is arguably one of the most paradoxical phenomena in plant evolution. Ferns are particularly interesting for addressing this issue because apomixis is more frequent than in any other group of plants. Here, we use a phylogenetic framework to explore some aspects of the evolution of apomixis in ferns and in particular in the polystichoid ferns. Our findings indicate that apomixis evolved several times independently in three different clades of polystichoid ferns. A lineage-wide perspective across ferns indicates a correlation between apomixis and the species richness of lineages; however BiSSE tests did not recover evidence for a correlation of apomixis and diversification rates. Instead, evidence was recovered supporting an association between the establishment of apomixis and reticulate evolution, especially in the establishment of triploid hybrids. Diversification time estimates supported the hypothesis of short living apomictic lineages and indicated a link between the establishment of apomixis and the strengthening of the monsoons caused by the lifting of the Qinghai-Tibetan plateau. In general our results supported the hypothesis for the rare establishment of apomictic lineages, high extinction risks, and low speciation rates.