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True land plants (embryophytes) evolved only once. Becker and Marin (pp. 999–1004) describe recent progress in our understanding of the early evolution of embryophytes from streptophyte algae. They present a hypothetical reconstruction of evolutionary events that led to the origin of the first land plants, and shaped the current diversity and ecology of streptophytes.
Host specificity in the parasitic plant Orobanche minor is quantified by Thorogood et al. (pp. 1005–1014) using cross-infection experiments. The data provide evidence that genetic races of O. minor are physiologically adapted to particular hosts. Host specificity may isolate races of Orobanche on different hosts, accelerating genetic divergence and ultimately speciation in the genus, and it is proposed that this mode of speciation may be a widespread phenomenon in parasitic plants. (Featured article in ContentSelect on p. iii.)
The small, submerged rosette plants called isoetids take up CO2 from sediment for photosynthesis. Winkel and Borum (pp. 1015–1023) show that sediment CO2 can support photosynthesis of other submerged rooted plants if they have a high root-to-shoot area ratio and high tissue porosity. (Featured article in ContentSelect on p. iii.)
Dry biomass includes the weights of a plant's structural and non-structural compounds, mostly carbohydrates, carboxylates, amino acids and minerals. Huanosto Magaña et al. (pp. 1025–1037) describe diel growth in tomato plantlets in terms of total and structural dry weight changes, highlighting large discrepancies in response to light and N nutrition. They emphasize the role played by C and N reserves in the uncoupling of resource use for growth from resource acquisition.
Interspecific hybridization and introgression are of wide occurrence in plant speciation. In intertribal crosses between Brassica rapa and Isatis indigotica made by Tu et al. (pp. 1039–1048), the hybrids show variations in morphology, chromosomal/genomic components and produce novel B. rapa types with altered genomic constitution or alien additions, suggesting that complete or partial chromosome elimination and diploidization with genomic rearrangements occur.
The sister tribes of Spermacoceae and Knoxieae in the Rubiaceae are essentially herbaceous. Using microscopic wood anatomical observations in combination with an independent molecular phylogeny, Lens et al. (pp. 1049–1064) find that all the woody Spermacoceae species observed are derived from herbaceous ancestors, while in Knoxieae there is a general trend from (primary) woodiness towards herbaceousness and back to (secondary) woodiness.
Cytinus hypocistis is a rootless, stemless and leafless holoparasitic plant whose flowers are only visible during the reproductive period when they arise from the host. de Vega et al. (pp. 1065–1075) conduct the first study of the pollination biology of this holoparasite, combining long-term field observations together with experimental pollination treatments, which reveal that ant mutualistic services are essential for the pollination of this Mediterranean biological oddity. (Featured article in ContentSelect on p. iv.)
The strength of self-incompatibility varies in F. cernua, a species showing pollen limitation. Ferrer et al. (pp. 1077–1089) find that poor availability of compatible mates may limit seed set in the species, and that self-fertility allows reproductive compensation in plants exhibiting either a partial or complete breakdown of self-incompatibility. Partial self-incompatibility may be favourable in this colonizing species, even though it maintains low levels of inbreeding. (Featured article in ContentSelect on p. iv.)
At dispersal, Lomatium dissectum seeds have under-developed embryos. Scholten et al. (pp. 1091–1101) find that these seeds have a deep, complex morphophysiological dormancy. Dormancy break and germination occur at low temperatures, but seeds from moist habitats have longer cold-stratification requirements than those from semi-arid environments. Interruption of cold stratification by dehydration results in loss of seed viability, or induced secondary dormancy.
Using the framework of a crop-emergence model, Brunel et al. (pp. 1103–1117) find genetic diversity during germination and pre-emergence growth in the model legume Medicago truncatula. A set of ecophysiological references is provided for M. truncatula users and the authors suggest such integrative characterizations are made before genetic or genomic analyses.
In a taxonomically diverse array of insect-pollinated Mediterranean plants, Herrera (pp. 1119–1127) examines within- and among-species variations in floral quantitative traits. Although isometric from the standpoint of corolla allocation, species with large, conspicuous flowers pay higher biomass costs per millimetre of display. Linear size is in general more steady than biomass. Any of the studied characteristics can vary significantly among populations.
The demography of pioneer-, early- and late-successional species and one ubiquitous species is studied by Marcante et al. (pp. 1129–1143) along a central alpine glacier foreland. Matrix modelling is used to classify species demography. All species over all successional stages behave like climax species in secondary successions. The overall dominance of survival indicates a major difference between primary and secondary succession.
The rays are generally considered as the main structure that serves radial transport in xylem. Kitin et al. (pp. 1145–1157) demonstrate that radial apoplastic transport can occur via a tracheid network (radial grain and tangential-wall pitting of tracheids) in a distinct pathway from that of the rays. They also show that intercellular spaces of rays form continuous canals across xylem rings.
Thermoregulation in the flower of the Asian sacred lotus, Nelumbo nucifera, has been hypothesized to offer a direct energy reward for pollinators. Using an artificial refrigeration instrument, Li and Huang (pp. 1159–1163) find that low floral temperature during the fertilization period significantly decreases seed production. Field pollination treatments confirm that a stable temperature is important in post-pollination events in lotus.