Moisture conditions and the presence of bryophytes determine fescue species abundance in a dry calcareous grassland

Festuca ovina is the abundant matrix-forming species and F. rubra a subordinate species in shallow-soil calcareous grasslands. F. pratensis is a transient species, occurring sparsely in this community. We hypothesised that the different abundances of these three species are primarily due to the differential effect of moisture conditions on their germination and early establishment, and that the effect of the pattern of rainfall intensity depends on the presence or absence of a bryophyte layer. We studied the dependence of the germination and establishment of the three fescue species on the moisture conditions both in the laboratory and in the patches of intact grassland community (microcosms). In a laboratory germination experiment, F. pratensis showed the highest, F. rubra , the intermediate and F. ovina, the lowest drought tolerance. In microcosms, the establishment of F. ovina was the highest. At the same time, the annual mortality of seedlings of F. ovina was the lowest. All three species responded positively to an increasing irrigation level. Differently from F. ovina, F. rubra showed a positive response only in plots from which the bryophyte layer had been removed, while F. pratensis responded positively to both irrigation and bryophyte removal. We conclude that moisture conditions have a differential effect on the three fescue species mainly in the seedling establishment, not in the germination phase. For the successful establishment of F. rubra and F. pratensis, the coincidence of high rainfall and local disturbance, removing bryophytes, is required. The presence or absence of bryophytes had no effect on establishment in dry years, while in rainy years the removal of bryophytes has a clear positive effect.     

The role of litter in an old-field community: impact of litter quantity in different seasons on plant species richness and abundance

Summary We studied the effect of removing and adding plant litter in different seasons on biomass, density, and species richness in a Solidago dominated old-field community in New Jersey, USA. We removed all the naturally accumulated plant litter in November (658 g/m²) and in May (856 g/m²) and doubled the amount of litter in November and May in replicated plots (1 m²). An equal number of plots were left as controls. Litter removal and addition had little impact on total plant biomass or individual species biomass in the growing season following the manipulations. Litter removal, however, significantly increased plant densities but this varied depending upon the season of litter removal, species, and life history type. Specifically, the fall litter removal had a much greater impact than the spring litter removal suggesting that litter has its greatest impact after plant senescence in the fall and prior to major periods of early plant growth in spring. Annual species showed the greatest response, especially early in the growing season. Both spring and fall litter removal significantly increased species richness throughout the study. Litter additions in both spring and fall reduced both plant densities and species richness in June, but these differences disappeared near the end of the growing season in September. We concluded than in productive communities where litter accumulation may be substantial, litter may promote low species richness and plant density. This explanation does not invoke resource competition for the decline in species richness. Finally, we hypothesize that there may be broad thresholds of litter accumulation in different community types that may act to either increase or decrease plant yield and diversity.     

Ethnobotany ofAnoda Cristata (L.) schl. (Malvaceae) in central Mexico: Uses, management and population differentiation in the community of Santiago Mamalhuazuca, Ozumba, state of Mexico

Anoda cristata is a common weed used for food and medicine in central Mexico where it grows among field crops during the rainy seasons. People prefer robust, tender plants from the agricultural fields because these “develop better.” Hence, the plants are tolerated within the conventional agricultural activities and benefit indirectly from the improvements in the agrohabitat. People do not select individuals with specific morphological characteristics but rather they select for plants at the level of the habitat. This step may precede that of direct management of individual plants. It is possible that these differences in the level of interaction between humans and plants (i.e., within the ruderal and agrestal habitats) may promote morphological and genetic differences over time,

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Etnobotánica de anoda cristata (Malvaceae) en México: Usos, Manejo y diferenciación poblacional en la Comunidad de Santiago Mamalhuazuca, Ozumba, estado de México

Resumen   Anoda cristata es una maleza muy común utilizada como medicina y alimento en el centro de México durante la época de lluvias La gente prefiere las plantas robustas y tiernas que crecen en los campos de cultivo porque se “desarrollan mejor.”Ahí, las plantas son toleradas dentro de las prácticas agrícolas tradicionales y se benefician indirectamente de las alteraciones que se hacen al agrohabitat. La gente no selecciona conscientemente individuos con características morfológicas específicas, sino que seleccionan a las plantas a nivel del hábitat. Este paso puede ser previo al manejo indirecto de individuos particulares. Es posible que estas diferencias en el nivel de interactión entre los hombres y las plantas (entre el hábitat ruderal y arvense) puede promover diferencias morfológicas y genéticas a través del tiempo.

     

Differences in AM fungal root colonization between populations of perennial Aster species have genetic reasons

We tested the hypothesis whether differences between plant populations in root colonization by arbuscular mycorrhizal (AM) fungi could be caused by genetic differentiation between populations. In addition, we investigated whether the response to AM fungi differs between plants from different populations and if it is affected by the soil in which the plants are cultivated. We used Aster amellus, which occurs in fragmented dry grasslands, as a model species and we studied six different populations from two regions, which varied in soil nutrient concentration.We found significant differences in the degree of mycorrhizal colonization of plant roots between regions in the field. To test if these differences were due to phenotypic plasticity or had a genetic basis, we performed a greenhouse experiment. The results suggested that Aster amellus is an obligate mycotrophic plant species with a high dependency upon mycorrhiza. Plant biomass was affected only by soil, and not by population or the interaction between the population and the soil. Mycorrhizal colonization was significantly affected by all three factors (soil, population, interaction of soil and population). Plants from the population originating from the soil with lower nutrient availability developed more mycorrhiza even when grown in soil with higher nutrient availability. The correspondence between mycorrhizal colonization of plants in the field and in both soils in the pot experiment suggests that the observed differences in root colonization have a genetic basis.     

Analysis of the molecular variation between and within cultivated and wild Pistacia species using AFLPs

Knowledge of pistachio genetic diversity is necessary for the formulation of appropriate management strategies for the conservation of these species. We analysed amplified fragment length polymorphisms in a total of 216 pistachio accessions, which included seven populations from three wild species (Pistacia vera, Pistacia khinjuk and Pistacia atlantica subsp. kurdica) and most of the important cultivars from Iran, together with some foreign cultivars. High levels of genetic diversity were detected within the Iranian cultivars, and they showed a clear separation from foreign cultivars, as revealed by unweighted pair group method with arithmetic averaging and supported by analysis of molecular variance. The lowest amount of polymorphism was observed in P. atlantica subsp. kurdica, which showed the lowest number of total bands as compared to the other species. This revealed strong genetic erosion of P. atlantica subsp. kurdica, which reflected a severe decline in habitat and over-exploitation. Based on these findings, strategies are proposed for the genetic conservation and management of pistachio species and cultivars.     

Ten new species of Tibouchina (Melastomataceae) from Mexico

Ten new species of Tibouchina (T. almedae, T. congestiflora, T. connata, T. hintonii, T. macvaughii, T. nanifolia, T. patens, T. roseotincta, T. sinaloensis, andT. thulia) are described from western Mexico. Distinguishing characteristics, phenology, distribution, and phylogenetic relationships are discussed. Illustrations of all these new species are provided.     

Three new species of Spigelia (Strychnaceae) from Mexico

During a revisionary study ofSpigelia, three new species from Mexico were discovered. Two of these new species appear to be narrow endemics, one in the state of Chiapas and one in the state of Guerrero, and the third is more widespread in Mexico and Guatemala. These new species are described, illustrated, and distinguished from other North AmericanSpigelias.     

Distribution and ecology ofCystopteris (Athyriaceae) species within the Flora Iranica region

The distribution ofCystopteris fragilis andC. dickieana in Afghanistan within the Flora Iranica region is studied. The latter species, for some ecological reason, occurs more frequently at higher altitudes. In both taxa higher polyploid levels also occur at high altitudes. The phenomenon can be correlated with the boreal-arctic distribution pattern. Polyploidism and spore-size classes are briefly mentioned as well as possible ecological adaptations. Evolutionary differentiation within both taxa are complex and still unknown.Dedicated to Univ.-Prof. DrK. H. Rechinger on the occasion of his 80th birthday and in recalling historical trips to the marvellous Afghan flora and vegetation.     

Quantifying phenotypic gradients in freshwater snails: a case study in Lithasia (Gastropoda: Pleuroceridae)

Many authors have described a pattern of morphological variation in freshwater bivalves where shells taken from lentic and lotic environments, or headwaters and main stem reaches, appear to exhibit phenotypic gradients in size and shape. For example, mussels taken from headwater reaches tend to possess smooth, less inflated shells compared to the more obese, sculptured individuals downstream. Others observed similar relationships in certain freshwater gastropods, but this variation has not been quantified nor its existence explained in an ecological or evolutionary context. Geometric morphometrics indicated freshwater snails shells from the pleurocerid genus Lithasia from the Duck River, Tennessee, USA, show phenotypic gradients similar to those in freshwater mussels. Shells from upstream areas were narrow and less sculptured on the posterior portions of their body whorls, while downstream shells were more inflated and possessed significantly more sculpture. This phenotypic variation may reduce predation or damage due to dislodging. The nature of the observed plasticity suggests an unidirectional environment similar to that proposed by the river continuum concept. Handling editor: K. Martens     

Testing the enemies hypothesis in forest stands: the important role of tree species composition

Numerous studies conducted in agro-ecosystems support the enemies hypothesis, which states that predators and parasites are more efficient in controlling pest densities in polycultures than in monocultures. Few similar studies, however, have been conducted in forest ecosystems, and we do not yet have evidence as to whether the enemies hypothesis holds true in forests. In a 2-year study, we investigated whether the survival of autumnal moth (Epirrita autumnata) larvae and pupae differs between silver birch monocultures and two-species mixtures of birch with black alder, Norway spruce and Scots pine. We placed young larvae on birch saplings and monitored their survival until the end of the larval period, when we checked whether they had been parasitized. After the larvae had pupated, pupal survival was tested in a field trial. In 2002, the larvae disappeared earlier and their overall survival was lower in birch–pine mixtures than in other stand types. In 2003, survival probability was lowest in birch–pine stands only during the first week and there were no differences between stands in overall survival. Larval parasitism was not affected by tree species composition. Pupal weight and pupal survival were likewise not affected by stand type. Among the predators, wood ants were more abundant on birches growing in birch–pine mixtures than in other stand types probably because colonies of myrmecophilic aphids were common on pines. In contrast, spider numbers did not differ between stand types. Ant exclusion by means of a glue ring around the birch trunk increased larval survival, indicating that ants are important predators of the autumnal moth larvae; differences in larval survival between stands are probably due to differential ant predation. Our results provide only partial support for the enemies hypothesis, and suggest that it is both tree species composition and species diversity which affect herbivore survival and predation.     

Three new species of Ocotea (Lauraceae) from southern Mexico

Three new species ofOcotea (O. disjuncta, O. iridescens, andO. rovirosae) from southern Mexico are described and illustrated.Ocotea disjuncta is related to theO. effusa group, whileO. iridescens seems to be related to theO. heydeana group. The relationships ofO. rovirosae are not clear.      

A new species in the Elaphoglossum petiolatum complex (Elaphoglossaceae) from Mexico

Elaphoglossum trichomidiatum is described from northeastern Mexico. The new species is a member of theE. petiolatum comples, which is widespread in tropical America, Africa, Southeast Asia, and the Pacific Islands. It is unique in the complex and in sectionLepidoglossa in bearing trichomidia on the abaxial blade surface.     

Three new species of ferns (Woodsiaceae and Polypodiaceae) from Mexico

Three new species of ferns are described from Mexico:Athyrium tripinnatum, Cystopteris millefolia, andPolypodium praetermissum.     

Variation on the population,racial, and species level in the primitive relic Angiosperm genusDrimys (Winteraceae) in South America

Statistical analyses and scatter diagrams illustrate for the polymorphic E. and SE. BrazilianDrimys brasiliensis a clear correlation between morphological variation and eco-geographical differentiation. This is backed by data on the (ultra)structure of the lower leaf surface. A new infraspecific taxonomy is proposed, andD. roraimensis andD. angustifolia are recognized as distinct species of the Guyana Highlands and S. Brazil, respectively. The affinities between these and other taxa of the paleopolyploid genus, its evolution and its position within the family are discussed.Dedicated to Prof.Lothar Geitler at the occasion of his 80th birthday.     

Thirteen new species and two new combinations of Stevia (Asteraceae: Eupatorieae) from Mexico

Thirteen new species of the genusStevia are described and illustrated from Mexico:S. chilapensis, S. coahuilensis, S. crassifolia, S. ecatepecana, S. filodecaballoana, S. mascotensis, S. mexicana, S. oaxacana, S. oligophylla, S. potosina, S. rotundifolia, S. scabrelloides, andS. viejoana. In addition, two varieties,Stevia aschenborniana Sch. Bip. ex Klotzsch var.occidentalis Grashoff andS. palmeri A. Gray var.constricta Grashoff are herein redefined as being distinct species,S. occidentalis andS. constricta stat. nov.Stevia mexicana resemblesStevia trifida Lagasca but differs in the habit.