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Aim This paper presents a synthesis of our recent results regarding the biogeography of Plagiochila using a molecular approach, and documents intercontinental ranges within this largest genus of the hepatics. Methods A maximum likelihood analysis of sixty‐one nrITS sequences of Plagiochila was performed and the molecular topology obtained was compared with morphological, phytochemical and geographical data. Results Our molecular data set allowed the identification of eleven Plagiochila sections, the majority of which cover at least two floristic kingdoms. Seven sections have species in Europe (sect. Arrectae, Carringtoniae, Fuscoluteae, Glaucescentes, Plagiochila, Rutilantes, Vagae). Plagiochila species from Atlantic Europe are usually close to or conspecific with neotropical taxa, whereas species widespread in Europe are closely related to Asian ones and not to those in the Neotropics. Plagiochila sect. Arrectae represents a neotropical – Atlantic European clade. The section is not closely related – as has often been suggested – to the morphologically similar sect. Zonatae from Asia and western North America. Sequence data show that the African P. integerrima and the neotropical P. subplana are members of the Asian sect. Cucullatae (sect. Ciliatae, syn. nov.), which becomes pantropical in distribution. An ITS sequence of P. boryana from Uganda confirms the Afro‐American range of the primarily neotropical sect. Hylacoetes. Similarities in sporophyte morphology between the sect. Cucullatae and sect. Hylacoetes are the result of parallel evolution. Main conclusions Our results indicate that intercontinental ranges at section and species level are common in Plagiochila. Carl's (1931) subdivision of Plagiochila into sections restricted to one floristic kingdom is outdated. Biogeographical patterns in Plagiochila are not dissimilar to those of other groups of bryophytes but elucidation of the geographical ranges of the taxa requires a molecular approach. Contrary to earlier belief, most Plagiochila species from Atlantic Europe do not have close relatives in Asia but are conspecific with or closely related to species from tropical America.

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In the production of concrete from cement powder and water, setting behavior of the slurry is determined by the formation of ettringite (Ca6Al2(OH)12 · (SO4)3 · 26 H2O) from tricalcium aluminate (Ca9Al6O18, abbreviated C3A) and gypsum (CaSO4 · 2 H2O). Due to the high reaction potential of cement and water, premature hydration can occur after unintentional exposure to moisture. Model binary mixtures of C3A and gypsum stored at 90% relative humidity and 35 °C produced ample amounts of ettringite, which subsequently reacted with atmospheric CO2 to CaCO3, Al(OH)3 and gypsum. Investigated were the two main polymorphs of tricalcium aluminate encountered in cement, pure, cubic C3A and orthorhombic C3A in which calcium is partially substituted by sodium or potassium. Alkali substituted C3A converted to ettringite faster and more completely than pure C3A. Ettringite from prehydration caused a seeding effect, which promotes crystal growth and accelerates bulk hydration of the C3A/gypsum mixtures. Set retarders commonly applied in cement were dissolved in the mixing water prior to hydration to investigate their ability to counteract this acceleration. Sodium gluconate merely delayed the crystal growth but does not prolong the hydration process overall. Potassium pyrophosphate retarded much more effectively by suppressing the seeding effect via removal of calcium ions from the hydration reaction.

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