Bamboo is well known for its fast growth and excellent mechanical performance, but since it lacks secondary-thickening it cannot use adaptive growth in the same way as a tree would in order to cope with bending stresses. Wang et al. examine the mechanical properties of single fibres and tissue slices of stems of mature moso bamboo (Phyllostachys pubescens) and latewood of spruce (Picea abies) and find that the superior tensile properties of bamboo fibres and fibre bundles are mainly a result of amplified cell-wall formation leading to a densely packed tissue, rather than being based on specific cell-wall properties. The material optimization towards extremely compact fibres with a multi-lamellar cell wall in bamboo might be a result of a plant growth strategy that compensates for the lack of secondary thickening growth at the tissue level.
Lizard orchids (Himantoglossum) include several of Eurasia’s most spectacular and conservation-relevant species. Sramkó et al. provide the first comprehensive molecular phylogeny for these charismatic orchids by sampling all known taxa across the whole distribution area of the genus. By using sequences of two nuclear and four plastid DNA-regions, they reconstruct phylogenetic trees that collectively determined the order of branching of the early divergent taxa as H. comperianum > H. robertianum group > H. formosum > H. hircinum group. Molecular clock and ancestral area analyses indicate an origin of the group at approximately 9 million years ago in the Caucasus Mountains.
Genomes of higher plants contain a spectrum of repetitive DNAs elements, and during genome restructuring these elements can be evolutionarily highly dynamic. Jang et al. examine the evolution of a novel satellite DNA, PaB6, in the chromosomally variable monocotyledonous genus Prospero. Although present in all three species, PaB6 has undergone differential amplification only in the P. autumnale complex, particularly in cytotypes that have experienced chromosomal fusions and genome size increases. The PaB6 copy numbers are among the highest for repetitive elements of any higher plant, and their changes are exceptionally dynamic in this group of closely related cytotypes within a single species.
Durum wheat (Triticum turgidum) is an important crop but grows poorly on acid soil because of its sensitivity to soluble Al3+. In contrast, hexaploid wheat (T. aestivum) possesses TaALMT1, a major gene for Al3+ tolerance located on chromosome 4D that is responsible for much of the variation in tolerance observed in this species. Han et al. introgress a fragment of the 4D chromosome containing TaALMT1 from hexaploid wheat into an elite durum cultivar and show that the fragment enhances root growth in acid soil. Since the Kna1 locus is also located on the chromosomal fragment, the ability of leaves to exclude Na+, a trait associated with salt tolerance, is also enhanced.
There seems to be a trade-off between height growth and mechanical stability in plants growing in crowded habitats. Watari et al. measure extension growth and mechanical properties of internodes in Xanthium canadense plants grown at different densities and show that tissue stiffness (Young’s modulus of elasticity) and strength (modulus of rupture) play crucial roles in maintaining stability in herbaceous species that lack the capacity for secondary growth. This differs from woody species where diameter growth has been considered more important.
Sex allocation can vary widely among flowers on a plant and among plants within a population. Austen and Weis develop a numerical model and use it to demonstrate that the widespread tendency towards declining fruit set from first to last flowers on plants may contribute to temporal variation in allocation optima. Temporal trends in relative pollen and ovule investment measured in Brassica rapa, however, do not match the predicted trends in functional gender, but some findings of the model, namely decreasing male reproductive success with later flowering onset, may nonetheless apply in this taxon.
Miscanthus sinensis is a perennial C4 grass that is one parent of the economically important hybrid biomass species, M. ×giganteus. Clark et al. evaluate 620 M. sinensis accessions from most of its native range with >20 000 nuclear and plastid markers, and identify six genetic groups. They find that coastal south-east China was a refugium of M. sinensis during the last glacial maximum, and that the species recolonized Japan prior to recolonizing similar latitudes in mainland Asia. Ornamental cultivars originate almost exclusively from southern Japan, and many marketed as M. sinensis have hybrid ancestry from M. sacchariflorus.
The pollinator-mediated stabilizing selection hypothesis suggests that the specialized pollination system of zygomorphic flowers might cause stabilizing selection, reducing their flower size variation compared to actinomorphic flowers. By using data on 43 species from two contrasting communities, Lázaro and Totland show that zygomorphic species that are highly dependent on pollinators and ecologically specialized are less variable in flower size than ecologically generalist and selfing zygomorphic species. However, these relationships are not found in actinomorphic species. The results suggest that the relationship between flower size variation and floral symmetry may be influenced by population-dependent factors, such as ecological generalization and species’ dependence on pollinators.
Olearia flocktoniae (Asteraceae) is an endangered shrub that was passively translocated from its natural ecosystem where it has since gone extinct. Gross and Mackay use two decades of demographic monitoring and a seed bank study in a sensitivity analysis in order to reveal vulnerabilities in the life cycle. They find that seed production is high but populations are short-term persistent (<5 years) due to transient seed banks and poor survivorship of seedlings. Seedling establishment is promoted by soil disturbance and only populations that have been disturbed annually survived the full 20 years of the study. They conclude that active management is thus required to keep this species from extinction.
Salvia (Lamiaceae) is the largest genus in the mint family, and phenotypic diversity of the genus in Africa is largely the result of repeated colonizations of the continent from different sources. Will and Claßen-Bockhoff produce a phylogenetic reconstruction and suggest that parallel character evolution is the rule rather than the exception in Old World Salvia. Notable examples are given by papery, conspicuously coloured calyces and repeated switches from bee- to bird-pollination. Different staminal lever types also evolved in parallel and should not be used any longer for characterizing major clades.