The taxonomic status and relationships of bracken ferns (Pteridium: Dennstaedtiaceae) from sub-Saharan Africa

Two morphotypes of bracken fern in the genus Pteridium Gled. ex Scop. occur in sub-Saharan Africa. The more common and widespread of these is assigned in contemporary systematic treatments to the European subspecies, P. aquilinum (L.) Kuhn ssp. aquilinum . We show that this African form is separable morphometrically and genomically from the European subspecies, and reinstate its earlier name P. aquilinum ssp. capense (Thunb.) C.Chr. The second African bracken, with a more localized tropical distribution mainly in the drainage basins of the Congo and Zambezi River systems, is confirmed as P. aquilinum ssp. centrali-africanum Hieron. ex R.E. Fr. We reject suggestions that this taxon be treated as a full species. Phenetic cluster analysis based on use of Arbitrarily Primed Polymerase Chain Reaction (A-P PCR) and Inter Simple Sequence Repeat (ISSR) fingerprinting of the nuclear genome provides evidence that the two African brackens are more closely related to each other than to other taxa, and sister to a grouping of the European sspp. aquilinum and pinetorum . The two African subspecies share solely with ssp. aquilinum a distinctive chloroplast haplotype carrying a 5-base direct repeat in the rps 4 –trn S region, confirming the close phyletic relationship between sspp. aquilinum , capense and centrali-africanum .  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 148 , 311–321.     

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

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 4 n  = 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.     

The taxonomy and phytogeography of bracken—a review

Some of the biological problems presented by bracken, Pteridium aquilinum (L.) Kuhn, are posed. Its taxonomic position within the Pteridophyta and the delimitation of entities within the genus are discussed on the basis of morphological and cytological evidence. The geographical ranges of the various brackens world-wide are described and mapped in outline, and emphasis placed on reviewing the natural ecological role of bracken in plant communities throughout the world. Further geographic areas where taxonomic investigation of Pteridium is most needed are indicated, and evidence of the reproductive, dispersal, establishment, colonizing ability and vegetative persistence of bracken is reviewed. Its palaeobiological spread, with associated vegetational history, and the effects on this of anthropogenic influences—better known than are comparable details for any other pteridophyte—are detailed, and the present magnitude of the resulting bracken problem in Britain (and especially in upland Britain) indicated.     

Chemotaxonomy and phytochemical ecology of bracken

Variations in flavonoids extracted from fronds suggest that Pteridium aquilinum (L.) Kuhn is a monospecific genus. A wide range of secondary plant substances also occur in bracken including sesquiterpenoids, echydones, cyanogenic glycosides, tannins and phenolic acids.     

Molecular phylogeny of Anthyllis spp

For the genus Anthyllis (Fam. Fabaceae, tribe Loteae), with few exceptions, little information is available on the genetic variation among and within species. This genus contains 20 species distributed throughout Europe, Africa, and the Mediterranean basin. The most widespread species is A. vulneraria, and over 30 intraspecies taxa have been identified based on plant morphology. To study the molecular phylogeny of the genus, the sequences of the internal transcribed spacers ITS1 and ITS2 of the nuclear ribosomal DNA of 10 Anthyllis species, including 11 subspecies of A. vulneraria and three subspecies of A. montana, were obtained and analysed together with sequences of five other species of the genus obtained from GenBank. Our results suggest that the genus Anthyllis is not monophyletic and is divided in two main clades: the Anthyllis sensu strictu and the "tetraphylla clade". The former includes most of the Anthyllis species, and the latter includes three annual species more closely related to Lotus. All the taxa were also analysed according to seven chloroplast microsatellites, and these data closely confirm the results obtained with the ITS phylogeny.     

Phylogeny and biogeography of the staghorn fern genus Platycerium (Polypodiaceae, Polypodiidae)

The genus Platycerium is one of the few pantropical epiphytic fern genera with six species in Afro-Madagascar, 8-11 Australasian species, and a single species in tropical South America. Nucleotide sequences of four chloroplast DNA markers are employed to reconstruct the phylogeny of these ferns and to explore their historical biogeography. The data set was designed to resolve conflicting hypotheses on the relationships within the genus that were based on previous phylogenetic studies exploring morphological evidence. Our results suggest a basal split of Platycerium into two well-supported clades. One clade comprises species occurring in Africa, Madagascar, and South America, whereas the second clade contains exclusively Australasian species. The latter clade is further divided into a clade corresponding to P. bifurcatum and its putative segregates and a clade of seven species occurring from Indochina throughout the Malesian region to New Guinea and Australia. The Afro-Madagascan clade includes a clade of two species found in tropical Africa and a clade of four species that includes three species endemic to Madagascar. The single neotropical species of this genus, P. andinum, is nested within the Afro-Madagascan clade but is not closely related to any extant species.     

Phylogenetic relationships in Bupleurum (apiaceae) based on nuclear ribosomal DNA its sequence data

BACKGROUND AND AIMS: The genus Bupleurum has long been recognized as a natural group, but its infrageneric classification is controversial and has not yet been studied in the light of sequence data. METHODS: Phylogenetic relationships among 32 species (35 taxa) of the genus Bupleurum were investigated by comparative sequencing of the ITS region of the 18-26S nuclear ribosomal DNA repeat. Exemplar taxa from all currently accepted sections and subsections of the genus were included, along with outgroups from four other early branching Apioideae genera (Anginon, Heteromorpha, Physospermum and Pleurospermum). RESULTS: Phylogenies generated by maximum parsimony, maximum likelihood, and neighbour-joining methods show similar topologies, demonstrating monophyly of Bupleurum and the division of the genus into two major clades. This division is also supported by analysis of the 5.8S coding sequence alone. The first branching clade is formed by all the species of the genus with pinnate-reticulate veined leaves and B. rigidum with a unique type of leaf venation. The other major clade includes the remaining species studied, all of which have more or less parallel-veined leaves. CONCLUSIONS: These phylogenetic results do not agree with any previous classifications of the genus. Molecular data also suggest that the endemic Macaronesian species B. salicifolium is a neoendemic, as the sequence divergence between the populations in Madeira and Canary Islands, and closer mainland relatives in north-west Africa is small. All endemic north-west African taxa are included in a single unresolved but well-supported clade, and the low nucleotide variation of ITS suggests a recent radiation within this group. The only southern hemisphere species, B. mundii (southern Africa), is shown to be a neoendemic, apparently closely related to B. falcatum, a Eurasian species.     

A re-evaluation of plants referred to as Pteridiutn herediae (Colmeiro) Love & Kjellqvist

SHEFFIELD, E., WOLF, P. G., HAUFLER, C. H., RANKER, T. A. & JERMY, A. C, 1989. Are-evaluation of plants referred to as Pteridiutn herediae (Colmeiro) Love & Kjellqvist. Based on perceived differences in morphology, chromosome number and habitat, specimens of Pteridiutn from southern Spain have been segregated by previous authors as a species distinct from Pteridium aquilinum , and called Pteridium herediae. However, type specimens of this taxon cannot be found. New collections of Pteridium from similar habitats in the area were examined and analysed in the present study and the results compared with those from British plants (P. aquilinum). The Spanish plants were not found to differ significantly from P. aquilinum morphologically, and all yielded chromosome counts (sporophytes, 104; gametophytes, 52) considered typical for the genus. Genotype frequency data obtained from isozyme electrophoresis of Spanish and British Pteridium yielded a genetic identity of 0.86; well within intraspecific distances found in other ferns.
These data indicate that there are currently no grounds for accepting that a form of Pteridium , distinguishable from P. aquilinum on the basis of differences in morphology, chromosome number, habitat or biochemistry, exists on the limestone soils of the Sierra de Cazorla region of southern Spain.     

Molecular phylogenetics, historical biogeography, and chromosome number evolution of Portulaca (Portulacaceae)

Portulaca is the only genus in Portulacaceae and has ca. 100 species distributed worldwide, mainly in the tropics and subtropics. Molecular data place the genus as one of the closest relatives of Cactaceae, but phylogenetic relationships within Portulaca are barely known. This study samples 59 species of Portulaca, 10 infraspecific taxa, and three cultivars, including multiple samples of widespread species. The sampled taxa represent all subgenera in the classifications of von Poellnitz (1934), Legrand (1958), and Geesink (1969) and come from around the world. Nuclear ITS and chloroplast ndhF, trnT-psbD intergenic spacer, and ndhA intron DNA sequences were analyzed using maximum likelihood and Bayesian methods to produce a hypothesis of relationships within Portulaca. Divergence times were estimated using Hawaiian endemics for calibration, and biogeographical patterns were examined using a Bayes-DIVA approach. In addition, the evolution of chromosome numbers in the genus was investigated using probabilistic models. The analyses strongly support the monophyly of Portulaca, with an age of the most recent common ancestor (MRCA) of 23 Myr. Within Portulaca are two major lineages: the OL clade (comprising opposite-leaved species) distributed in Africa, Asia, and Australia, and the AL clade (comprising alternate to subopposite-leaved species), which is more widespread and originated in the New World. Sedopsis, a genus sometimes recognized as distinct from Portulaca based on a long corolla tube, is nested within the OL clade and does not merit taxonomic recognition. Samples of Portulaca grandiflora, Portulaca halimoides, and Portulaca oleracea were found to be non-monophyletic. It is hypothesized that the ancestral distribution area of Portulaca included southern hemisphere continents and Asia. The OL clade remained restricted to the Old World (except Portulaca quadrifida, a pantropical weed), while the AL clade, with a South American origin, was able to disperse multiple times to other continents. The base chromosome number for Portulaca is inferred to be x=9, although the analysis was primarily based on the available data for the AL clade. A number of chromosome number change events (polyploidization, demi-polyploidization, gain, and loss) were shown to have occurred in the genus, especially within the Oleracea clade.     

Phylogenetic analysis of Pinguicula (Lentibulariaceae): chloroplast DNA sequences and morphology support several geographically distinct radiations

The genus Pinguicula is one of the three genera of the carnivorous Lentibulariaceae, comprising approximately 80 species. Phylogeny inference using nucleotide sequences of the chloroplast gene matK and the trnK group II intron, as well as a set of 32 morphological characters revealed five well-supported, major lineages within the genus. These lineages largely reflect radiations in clearly defined geographic regions, whereas most previously recognized sections of the genus are shown to be para- or polyphyletic. A species-rich Mexican-Central American-Caribbean clade has the Eurasian P. alpina and an East Asian clade as successive sisters. All three are characterized by a production of flower buds on winter-resting plants, a specific corolla hair structure and a very large corolla lower central lobe. Another diverse clade is composed of species with primarily European distribution including the widespread type species P. vulgaris. For this clade, vegetative reproduction during dormancy is synapomorphic. Species native to SE North America and the South American Andes and a group of Mediterranean and NE Atlantic coast species together appear in a fifth well-supported clade, that is characterized by a tropical-type growth habit. It is the only clade that has reached temperate zones of the southern hemisphere.     

A CHLOROPLAST-DNA PHYLOGENY OF THE WILD PERENNIAL RELATIVES OF SOYBEAN (GLYCINE SUBGENUS GLYCINE): CONGRUENCE WITH MORPHOLOGICAL AND CROSSING GROUPS

Hypotheses of evolutionary relationships among the Australian wild perennial relatives of soybean (Glycine subgenus Glycine) are based largely on patterns of meiotic pairing in intra- and interspecific experimental hybrids. This evidence has indicated a number of genome groupings within the subgenus but has not resolved most phylogenetic relationships. Restriction-endonuclease site variation of chloroplast DNA (cpDNA) within the perennial subgenus is reported here, representing a sampling of approximately 3% of the approximately 150-kilobase plastome. Seven hundred twenty-one unique restriction sites were compared within Glycine using 29 restriction endonucleases; 157 sites varied within the genus. Distance and parsimony methods using these data yielded congruent results, recognizing the existence of three major groups within subgenus Glycine: the species-rich and geographically diverse A clade consisting of G. canescens and related taxa; the B clade, which includes the stoloniferous species; and the C group, containing two species with distinctive curved pods. These results are in general agreement with hypotheses based on genome analysis; inconsistencies involve the inclusion of genetically divergent taxa such as G. falcata in well-supported plastome clades comprised of otherwise interfertile species. Such findings are not unexpected if crossing barriers are considered to be unique features of such anomalous species, paralleling their often numerous morphological and cpDNA autapomorphies. Consideration of cpDNA divergence within the three major clades of subgenus Glycine indicates that the rate of plastome evolution is uncoupled from rates of morphological or ecological diversification.     

Molecular phylogeny and evolution of Caricaceae based on rDNA internal transcribed spacers and chloroplast sequence data

This study focused on clarifying phylogenetic relationships and evolution within Caricaceae. Our phylogenetic analysis based on nucleotide sequences from the ITS of the ribosomal DNA and three chloroplast fragments (matK, trnL-trnF, and psbA-trnH) included 29 taxa belonging to five genera: the neotropical genera Carica, Vasconcellea, Jarilla, and Jacaratia and the equatorial African genus Cylicomorpha. Having a relatively low mutation rate, matK, and trnL-trnF were used for estimating relationships at the generic level, while intrageneric evolution within Vasconcellea was studied with the more variable ITS and psbA-trnH sequences. Gaps, coded as binary characters, were added to the sequence alignments before performing Maximum Parsimony and Maximum Likelihood analyses. Monophyly of Caricaceae as well as phylogenetic distance between Carica and Vasconcellea species, previously belonging to the same genus, and monophyly of the resurrected genus Vasconcellea were emphasized. Within Vasconcellea, the largest genus of this family, two well-confirmed evolutionary lineages could be discerned: (1) V.xheilbornii, V. weberbaueri, V. stipulata, and V. parviflora and (2) a clade holding all other taxa of the genus. Incongruence between nuclear ITS and chloroplast psbA-trnH datasets, shown to be significantly caused by some taxa of the genus Vasconcellea, indicated that reticulate events in this genus might be more frequent than previously suspected. Moreover, intra-individual ITS sequence heterogeneity provided further evidence for the hybrid or introgressed origin of different taxa and one presumed hybrid belonging to this genus.     

Phylogenetic relationships of Pterocarya (Juglandaceae) with an emphasis on the taxonomic status of Iranian populations using ITS and trnH-psbA sequence data

Pterocarya fraxinifolia (Lam.) Spach., a relict tree species of the Juglandaceae family, is native to the Great Caucasus, Anatolia, and to the Hyrcanian forests of the southern Azerbaijan and Northern Iran. In this study, the phylogenetic relationship of the species, sampled in selected Iranian populations, and the global biogeography of the genus Pterocarya were addressed. Leaves were collected from 8 to 10 trees from three geographically isolated habitats. The samples were analyzed with nuclear (internal transcribed spacer [ITS] regions) and chloroplast (trnH-psbA) DNA markers. The obtained results were compared and analyzed with the data registered in NCBI GenBank. It is reported that the ITS regions varied from 644 to 652 for Pterocarya genus, but we did not observe polymorphisms for Iranian Pterocarya. The phylogenetic tree divided the Pterocarya genus in three clades: clade 1 grouping exclusively the samples P. fraxinifolia, clearly separated from the East Asiatic taxa; clade 2 that includes the species P. hupehensis and P. macroptera; clade 3 clustering P. stenoptera and P. tonkinensis. Although the Iranian Pterocarya samples and P. fraxinifolia from the Caucasus were in the same clade, they presented two different secondary structures. The Iranian populations showed the maximum genetic distance with P. stenoptera and P. tonkinensis. Our analysis demonstrates that the traditional division of all the six species sampled throughout their distribution area as well as the phylogeny of the genus Pterocarya needs to be reviewed.     

Bracken-induced increase in soil P availability,along with its high P acquisition efficiency,enables it to invade P-deficient meadows

欧洲蕨入侵提高了土壤磷有效性和高磷获取效率 对于欧洲蕨(Pteridium aquilinum)入侵荒地后土壤化学的变化,已经有了相关的研究,但是对于欧洲蕨入侵草地的研究却比较缺乏。本研究探讨了欧洲蕨入侵缺磷草地是否会改变土壤养分资源库,以及与土壤过程和欧洲蕨营养相关的机制。此外,还研究了欧洲蕨入侵前后群落组成对土壤化学差异的反应。在蕨菜生物量高峰期间,我们进行了土壤和植物取样以及植被调查。数据分析包括方差分析(ANOVA)和典型对应分析(CCA)。研究结果表明,欧洲蕨入侵提高了土壤磷有效性、土壤有机碳浓度以及碳氮比、碳硫比和氮硫比,同时降低了铁和钴的浓度。欧洲蕨羽片富含磷,根茎富含钾,而羽片 和根茎的氮磷比很低。典型对应分析(CCA)显示了与磷和钾有效性相关的常见草地植物物种的不同丰度模式。在磷有效性极低的条件下,绒毛草(Holcus lanatus)表现出竞争优势。欧洲蕨通过促进铁和铝的浸出提高了磷有效性。从土壤资源生态位的角度来看,欧洲蕨通过提高自身生长所需的磷有效性并且增加对其他物种的氮限制,从而获得了竞争优势。欧洲蕨提高土壤磷有效性的能力,以及其高磷获取效率背后的生理机制,似乎将欧洲蕨与其他竞争生态策略的物种区分开来,因为其他物种的生长主要局限于营养丰富的环境,因此欧洲蕨更容易入侵缺磷的草地。     

Phylogeny and historical biogeography of African ground squirrels: the role of climate change in the evolution of Xerus

We used phylogenetic and phylogeographical methods to infer relationships among African ground squirrels of the genus Xerus. Using Bayesian, maximum-parsimony, nested clade and coalescent analyses of cytochrome b sequences, we inferred interspecific relationships, evaluated the specific distinctness of Cape (Xerus inauris) and mountain (Xerus princeps) ground squirrels, and tested hypotheses for historical patterns of gene flow within X. inauris. The inferred phylogeny supports the hypothesized existence of an 'arid corridor' from the Horn of Africa to the Cape region. Although doubts have been raised regarding the specific distinctness of X. inauris and X. princeps, our analyses show that each represents a distinct well-supported, monophyletic lineage. Xerus inauris includes three major clades, two of which are geographically restricted. The distributions of X. inauris populations are concordant with divergences within and disjunctions between other taxa, which have been interpreted as results of Plio-Pleistocene climate cycles. Nested clade analysis, coalescent analyses, and analyses of genetic structure support allopatric fragmentation as the cause of the deep divergences within this species.     

Molecular systematics of a speciose, cosmopolitan songbird genus: defining the limits of, and relationships among, the Turdus thrushes

The avian genus Turdus is one of the most speciose and widespread of passerine genera. We investigated phylogenetic relationships within this genus using mitochondrial DNA sequence data from the ND3, ND2 and cytochrome b genes. Our sampling of Turdus included 60 of the 65 extant species currently recognized, as well as all four species from three genera previously shown to fall inside Turdus (Platycichla, Nesocichla, and Cichlherminia). Phylogenetic trees based on maximum likelihood and maximum parsimony algorithms were congruent. Most of the Turdus taxa sampled fall into one of four clades: an African clade, a Central American-Caribbean clade, a largely South American clade, and a Eurasian clade. Still other taxa are placed either at the base of Turdus, or as links between clades. In no instance is any continent reciprocally monophyletic for the species distributed on it. A general lack of nodal support near the base of the phylogeny seems related to a rapid intercontinental establishment of the major clades within Turdus very early in the history of the genus. The monotypic genus Psophocichla is distantly related to, but clearly the sister of, Turdus rather than a constituent member of it.     

The ecological status of bracken

Information about the morphology of bracken ( Pteridium aquilinum (L.) Kuhn var. aquilinum ) and the chief nutrients in the frond at different times of the year introduce an account of litter production and its accumulation in relation to the behaviour of frond, root and rhizome systems.
Where litter gain exceeds loss there is a correlation between the thickness and/or kind of litter and the level of the root and rhizome systems in relation to the mineral soil surface: with increase of litter the bracken becomes progressively more dependent for its physical and chemical soil environment on its own débris and less on the underlying mineral soil. An example of the limit of complete dependence has not been examined, but degeneration of the community can take place before that stage is reached.
From a review of the chief factors affecting bracken the conclusion is reached that the woodland habitat is both favourable and restrictive: in it bracken is in equilibrium with its environment, at a high social status. The relationship with other plant communities depends largely on the degree of human interference to which each is subject. Dominant bracken when left alone, and where gain of litter exceeds loss, becomes the victim of its own success; local degeneration opens the way for entry by other species.     

Phylogenetic origins of Lophocereus (Cactaceae) and the senita cactus-senita moth pollination mutualism

Recent ecological research has revealed that the Sonoran Desert columnar cactus Lophocereus and the pyralid moth Upiga virescens form an obligate pollination mutualism, a rare but important case of coevolution. To investigate the phylogenetic origins of this unusual pollination system, we used molecular sequence data to reconstruct the phylogeny of the four taxa within the genus Lophocereus and to determine the phylogenetic position of Lophocereus within the North American columnar cacti (tribe Pachycereeae). Our analysis included Lophocereus, six Pachycereus species, Carnegiea gigantea, and Neobuxbaumia tetetzo within the subtribe Pachycereinae, and Stenocereus thurberi as an outgroup within the Stenocereinae. Extensive screening of chloroplast and mitochondrial genomes failed to reveal sequence variation within Lophocereus. At a deeper phylogenetic level, however, we found strong support for the placement of Lophocereus within Pachycereus as sister group to the hummingbird-pollinated P. marginatus. We discuss possible hypotheses that may explain the transition from bat pollination (ancestral) to moth and hummingbird pollination in Lophocereus and P. marginatus, respectively. Additional phylogenetic analyses suggest that the genus Pachycereus should be expanded to include Lophocereus, Carnegiea, Neobuxbaumia, and perhaps other species, whereas P. hollianus may need to be excluded from this clade. Future study will be needed to test taxonomic distinctions within Lophocereus, to test for parallel cladogenesis between phylogroups within Lophocereus and Upiga, and to fully delineate the genus Pachycereus and relationships among genera in the Pachycereinae.