Genetic diversity and breeding system in a group of neotropical epiphytic ferns (Pleopeltis; Polypodiaceae)

Epiphytes are ecologically important components of tropical forests worldwide and yet they have been underrepresented in studies of reproductive biology. Given the presumed ephemeral nature of their substrates, and the importance of dispersal and colonization, epiphytes might be expected to undergo substantial inbreeding to ensure reproductive success, as in weedy terrestrial plants. While there is some evidence for inbreeding in epiphytic angiosperms, the only previous studies of fern epiphytes indicate that they are predominantly outcrossing. The present study reports on the genetic diversity and breeding system of six members of the Neotropical epiphytic fern genus Pleopeltis (Polypodiaceae). A survey of isozyme variability using starch gel electrophoresis revealed high population levels of polymorphism (P = 0.62), allelic diversity (A = 2.3), and individual heterozygosity (Ho = 0.181), but little differentiation among conspecific populations (I 3 0.98; Gst = 0.048), and high interpopulational gene flow rates (Nm > 1). In addition, there was no indication of homozygote excess within populations that might indicate a history of selfing in these ferns: populations generally conformed to Hardy-Weinberg expected genotype frequencies, and both Wright's inbreeding coefficient (Fis) and Holsinger's intragametophytic selfing rates approached zero. Possible mechanisms limiting inbreeding in these ferns include antheridiogen activity and high levels of genetic load that would lead to inbreeding depression upon selfing.     

Distribution of glycolipids and phospholipids in Pteridium aquilinum

The glycolipids and phospholipids in fronds and rhizomes of Pteridium aquilinum were determined. The total quantity of polar lipid decreased towards the base of the frond, but increased in the storage rhizome. The monogalactosyl diglyceride/digalactosyl diglyceride ratio was 1.8 in the pinnae, 1.0 in the lower petiole and 0.3 in the storage rhizome.     

Taxonomic revision of Lepisorus （J. Sm.） Ching sect. Lepisorus （Polypodiaceae） from China

The taxonomy of Lepisorus （J. Sm.） Ching sect. Lepisorus in China was revised based on herbarium specimen examinations, field observations, and microscopic study of rhizome scales, soral paraphyses, leaf epidermis, and spores. As a result, nine species were recognized： Lepisorus macrosphaerus （Baker） Ching, Lepisorus asterolepis （Baker） Ching, Lepisorus marginatus Ching, Lepisorus kuchenensis （Y.C. Wu） Ching, Lepisorus megasorus （C. Chr.） Ching, Lepisorus kawakamii （Hayata） Tagawa, Lepisorus subsessilis Ching ＆ Y.X. Lin, Lepisorus affinis Ching, and Lepisorus nudus （Hook.） Ching. Lepisorus kawakamii （Hayata） Tagawa was reinstated; Lepisorus gyirongensis Ching ＆ S.K. Wu and Lepisorus longus Ching were reduced to synonyms ofL. nudus and L. affinis, respectively. The subdivision ofLepisorus macrosphaerus was not accepted. Rhizome scales and paraphyses are the most useful characters for species delimitation as well as for infrageneric classification. Characteristics of the leaf epidermis and spore ornamentation are usually stable and thus of great significance in understanding the relationships among groups within the genus.     

Hydrocarbons and fatty acids of ferns

The analysis of hydrocarbons and fatty acids in ten fern species indicate unique differences from plants in a higher phylogenetic order. Significant concentrations of fatty acids above C₂₀ are present. Distributions of hydrocarbons range from C₁₅–C₃₃ with a trend towards two maxima at C₁₇ and C₂₉. Homologous series of n-alkenes are present in all species. Pristane and phytane are large components representing up to 27% of the alkanes. Distinct alkane and fatty acid differences between fern families are observed while species variations within families are slight.     

A Supplement to the 《Flora of Xizang》 (2)

The present paper is the Supplement 2 to the Flora of Xizang, based upon a collection in 1980 by Mr. W. L. Chen et al. from Mêdog, the south-eastern part of Xizang. In the paper 11 new species are desribed and 10 new-record species are reported. All the type specimens are kept in the Herbarium of the Institure of Botany, Academia Sinica (PE).     

Exploring the evolution of humus collecting leaves in drynarioid ferns (Polypodiaceae, Polypodiidae) based on phylogenetic evidence

Most species of the paleotropic fern genera Aglaomorpha and Drynaria, together constituting a monophyletic clade (drynarioid ferns), possess humus-collecting structures as an adaptation to their epiphytic life form. Humus-collectors are either present as a specialized foliar structure (external leaf dimorphism) or as a specialized leaf part (internal dimorphism). Apart from these basic patterns there are several forms of reduction and an internal fertile – sterile dimorphism in Aglaomorpha. We present a phylogeny of drynarioid ferns based on morphological and molecular (cpDNA) markers. The genus Aglaomorpha was found to be monophyletic, whereas Drynaria is likely to be a paraphyletic assemblage including a grade of Himalayan to Southern Chinese taxa basal to Aglaomorpha. The evolution of humus-collectors is reconstructed by plotting their character state changes onto the obtained phylogeny. Despite the complex morphological pattern across species, evolution of drynarioid humus-collecting structures can be reconstructed postulating a simple sequence of character state changes based on only a few elementary processes.     

Fern constituents: Cycloartane triterpenoids and allied compounds from Polypodium formosanum and P. niponicum

From the rhizomes of Polypodium formosanum, new triterpenoids of the cycloartane group, (24R)-cyclolaudenol and (24R)-cyclomargenol, were isolated as the corresponding acetates, alcohols and ketones, and their structures were established. Also, from the rhizomes of P. niponicum eight acetates of cycloartane derivatives and two acetates of new methyl sterols were isolated and characterized.     

Gymnogrammitis dareiformis is a polygrammoid fern (Polypodiaceae) – Resolving an apparent conflict between morphological and molecular data

 Maximum parsimony and maximum likelihood analyses of the combined data sets of two chloroplast genes, rbcL and rps4, demonstrate that nk;the monotypic genus Gymnogrammitis is part of the polygrammoid clade (Polypodiaceae + Grammitidaceae), and not the Davalliaceae as proposed in most studies. The genus forms a clade together with two Asiatic genera of the Polypodiaceae, Arthromeris and Selliguea. These last two genera have either simple or once-pinnate leaves, whereas Gymnogrammitis has highly divided (3- to 4-pinnate) blades. Two characters of this genus, the basic chromosome number of x=36 and the absence of indusia, support a relationship with the Polypodiaceae. Neither feature is found within Davalliaceae. Three morphological characters support the placement of Gymnogrammitis within the selligueoid lineage of Polypodiaceae: spores with a thick perine extending in microspines, sclerenchymatous strands in the rhizome, and non-clathrate rhizome scales. These results demonstrate that molecular and morphological data are phylogenetically congruent with the exception of blade dissection. Our study clearly shows the pitfalls of classifications based on single characters, and illustrates the importance of phylogenetic assessment of all taxonomic conclusions. Received November 22, 2001; accepted May 21, 2002 Published online: November 14, 2002 Addresses of the authors: Harald Schneider (e-mail: hschneid@duke.edu), Department of Biology, Duke University, Durham, North Carolina, 27708, USA; Current address: Albrecht-von-Haller Institut für Pflanzenwissenschaften der Universit?t G?ttingen, Abteilung Systematische Botanik, Untere Karspüle 2, D-37073 G?ttingen, Germany. Alan R. Smith, Ray Cranfill, University Herbarium, University of California, Berkeley, California 94720-2465, USA. Christopher H. Haufler, Terri Hildebrand, Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, Kansas 66045, USA. Tom A. Ranker, University Museum and Department of Environmental, Population, and Organismic Biology, University of Colorado, Boulder, Colorado 80309, USA.     

Higher clonal integration in the facultative epiphytic fern Selliguea griffithiana growing in the forest canopy compared with the forest understorey

Background and Aims The advantage of clonal integration (resource sharing between connected ramets of clonal plants) varies and a higher degree of integration is expected in more stressful and/or more heterogeneous habitats. Clonal facultative epiphytes occur in both forest canopies (epiphytic habitats) and forest understories (terrestrial habitats). Because environmental conditions, especially water and nutrients, are more stressful and heterogeneous in the canopy than in the understorey, this study hypothesizes that clonal integration is more important for facultative epiphytes in epiphytic habitats than in terrestrial habitats.Methods In a field experiment, an examination was made of the effects of rhizome connection (connected vs. disconnected, i.e. with vs. without clonal integration) on survival and growth of single ramets, both young and old, of the facultative epiphytic rhizomatous fern Selliguea griffithiana (Polypodiaceae) in both epiphytic and terrestrial habitats. In another field experiment, the effects of rhizome connection on performance of ramets were tested in small (10 × 10 cm²) and large (20 × 20 cm²) plots in both epiphytic and terrestrial habitats.Key Results Rhizome disconnection significantly decreased survival and growth of S. griffithiana in both experiments. The effects of rhizome disconnection on survival of single ramets and on ramet number and growth in plots were greater in epiphytic habitats than in terrestrial habitats.Conclusions Clonal integration contributes greatly to performance of facultative epiphytic ferns, and the effects were more important in forest canopies than in forest understories. The results therefore support the hypothesis that natural selection favours genotypes with a higher degree of integration in more stressful and heterogeneous environments.