New insights into the origin of buckwheat cultivation in southwestern China from pollen data.

Buckwheat is an important crop which originated in China and spread widely across Eurasia. However, exactly where in China domestication took place remains controversial. Archaeological and palynological records suggest a longer cultivation history of buckwheat in northern China than in southwestern China, but this conflicts with phylogenetic evidence implicating southwestern China as the centre of origin and diversity of buckwheat. We investigate alternative methodologies for inferring the occurrence of buckwheat cultivation and suggest that relative abundance could provide a reliable measure for distinguishing between wild and cultivated buckwheat in both present-day and fossil samples. Approximately 12 800-yr palaeoecological record shows that Fagopyrum pollen occurred only infrequently before the early Holocene. As southwestern China entered the early agricultural period, c. 8000-7000 yr ago, a slight increase in abundance of Fagopyrum pollen was observed. Approximately 4000 yr ago, concurrent with the Pu minority beginning to develop dry-land agriculture, the abundance of Fagopyrum pollen increased significantly, suggesting the cultivation of this crop. Fagopyrum pollen rose to a maximum value c. 1270 yr ago, suggesting an intensification of agricultural activity. These findings fill a gap in the Fagopyrum pollen record in southwestern China and provide new indications that early cultivation may have occurred in this region.

Herbaria are a major frontier for species discovery.

Despite the importance of species discovery, the processes including collecting, recognizing, and describing new species are poorly understood. Data are presented for flowering plants, measuring quantitatively the lag between the date a specimen of a new species was collected for the first time and when it was subsequently described and published. The data from our sample of new species published between 1970 and 2010 show that only 16% were described within five years of being collected for the first time. The description of the remaining 84% involved much older specimens, with nearly one-quarter of new species descriptions involving specimens >50 y old. Extrapolation of these results suggest that, of the estimated 70,000 species still to be described, more than half already have been collected and are stored in herbaria. Effort, funding, and research focus should, therefore, be directed as much to examining extant herbarium material as collecting new material in the field.

An assessment of potential diatom "barcode" genes (cox1, rbcL, 18S and ITS rDNA) and their effectiveness in determining relationships in Sellaphora (Bacillariophyta).

Due to limited morphological differentiation, diatoms can be very difficult to identify and cryptic speciation is widespread. There is a need for a narrower species concept if contentious issues such as diatom biodiversities and biogeographies are to be resolved. We assessed the effectiveness of several genes (cox1, rbcL, 18S and ITS rDNA) to distinguish cryptic species within the model 'morphospecies', Sellaphora pupula agg. This is the first time that the suitability of cox1 as an identification tool for diatoms has been assessed. A range of cox1 primers was tested on Sellaphora and various outgroup taxa. Sequences were obtained for 34 isolates belonging to 22 Sellaphora taxa and three others (Pinnularia, Eunotia and Tabularia). Intraspecific divergences ranged from 0 to 5bp (=0.8%) and interspecific levels were at least 18bp (=c. 3%). Cox1 divergence was usually much greater than rbcL divergence and always much more variable than 18S rDNA. ITS rDNA sequences were more variable than cox1, but well-known problems concerning intragenomic variability caution against its use in identification. More information and less sequencing effort mean that cox1 can be a very useful aid in diatom identification. The usefulness of cox1 for determining phylogenetic relationships among Sellaphora species was also assessed and compared to rbcL. Tree topologies were very similar, although support values were generally lower for cox1.

Pollen-based reconstruction of vegetational and climatic change over the past ~30 ka at Shudu Lake in the Hengduan Mountains of Yunnan, southwestern China.

The Hengduan Mountains, with a distinct altitudinal differentiation and strong vertical vegetation zonation, occupy an important position in southwestern China as a global hotspot of biodiversity. Pollen analysis of lake sediments sampled along an altitudinal gradient in this region helps us to understand how this vegetation zonation arose and how it has responded to climate change and human impacts through time. Here we present a ~30-ka pollen record and interpret it in terms of vegetational and climatic change from a 310 cm-long core from Shudu Lake, located in the Hengduan Mountains region. Our results suggest that from 30 to 22 cal. ka BP, the vegetation was dominated by steppe/grassland (comprising mainly Artemisia, Poaceae and Polygonaceae) and broad-leaved forest (primarily Quercus, Betula and Castanopsis) in the lake catchment, reflecting a relatively warm, wet climate early in this phase and slightly warmer, drier conditions late in the phase. The period between 22 and 13.9 cal. ka BP was marked by a large expansion of needle- and broad-leaved mixed forest (Pinus, Abies and Quercus) and a decline in the extent of steppe/grassland, indicating warming, drying climatic conditions followed by a cold, wet period. Between 13.9 and 3 cal. ka BP, steppe/grassland expanded and the area covered by needle- and broad-leaved mixed forest reduced, implying a fluctuating climate dominated by warm and humid conditions. After 3 cal. ka BP, the vegetation was characterized by an increase in needle-leaved forest and reduction in steppe/grassland, suggesting warming and drying climate. A synthesis of palynological investigations from this and other sites suggests that the vegetation succession patterns seen along an altitudinal gradient in northwestern Yunnan since the Late Pleistocene are comparable, but that each site has its own characteristics probably due to the influences of altitude, topography, microclimate and human impact.

A MOLECULAR SYSTEMATIC APPROACH TO EXPLORE DIVERSITY WITHIN THE SELLAPHORA PUPULA SPECIES COMPLEX (BACILLARIOPHYTA)(1).

The common and cosmopolitan freshwater benthic diatom Sellaphora pupula (Kütz.) Mereschk. is a model system for studying the nature of species in microalgae; the biological significance of morphological variation in this species complex has been widely demonstrated. The aim of this study was to establish a two-gene phylogeny (18S rDNA and rbcL) for 23 Sellaphora taxa, including 19 S. pupula aggregate (agg.) demes or species, S. bacillum (Ehrenb.) D. G. Mann, and S. laevissima (Kütz.) D. G. Mann. A range of analyses on separate and combined data sets indicated that Sellaphora is a monophyletic group containing four major clades. Of the traditionally recognized species, S. bacillum and S. laevissima are natural groups, but S. pupula is paraphyletic or polyphyletic because S. bacillum groups with S. pupula"small lanceolate" and S. lanceolata. Thickened bars at the poles of valves within the core "pupula-bacillum" group may be a morphological synapomorphy; the fossil record suggests that this group is at least 12 million years old. Otherwise, there was no clear pattern in the distribution of different morphologies among the major clades; each clade was also heterogeneous with respect to mating system. More intensive and extensive sampling will doubtless uncover even greater diversity; the challenge lies in its interpretation. Our results demonstrate the limitations of paleoecological, ecological, and biogeographical research based on morphospecies.

Pollen wall development in flowering plants.

The outer pollen wall, or exine, is more structurally complex than any other plant cell wall, comprising several distinct layers, each with its own organizational pattern. Since elucidation of the basic events of pollen wall ontogeny using electron microscopy in the 1970s, knowledge of their developmental genetics has increased enormously. However, self-assembly processes that are not under direct genetic control also play an important role in pollen wall patterning. This review integrates ultrastructural and developmental findings with recent models for self-assembly in an attempt to understand the origins of the morphological complexity and diversity that underpin the science of palynology.

How much data are needed to resolve a difficult phylogeny?: case study in Lamiales.

Reconstructing phylogeny is a crucial target of contemporary biology, now commonly approached through computerized analysis of genetic sequence data. In angiosperms, despite recent progress at the ordinal level, many relationships between families remain unclear. Here we take a case study from Lamiales, an angiosperm order in which interfamilial relationships have so far proved particularly problematic. We examine the effect of changing one factor-the quantity of sequence data analyzed-on phylogeny reconstruction in this group. We use simulation to estimate a priori the sequence data that would be needed to resolve an accurate, supported phylogeny of Lamiales. We investigate the effect of increasing the length of sequence data analyzed, the rate of substitution in the sequences used, and of combining gene partitions. This method could be a valuable technique for planning systematic investigations in other problematic groups. Our results suggest that increasing sequence length is a better way to improve support, resolution, and accuracy than employing sequences with a faster substitution rate. Indeed, the latter may in some cases have detrimental effects on phylogeny reconstruction. Further molecular sequencing-of at least 10,000 bp-should result in a fully resolved and supported phylogeny of Lamiales, but at present the problematic aspects of this tree model remain.