The appearance and dramatic radiation of angiosperm in the Cretaceous was one of the major biotic upheavals in the history of life. This late and apparent sudden arrival of angiosperms, almost 300 mil-lion years after the first land plants started to colonize Earth, was a puzzle to Darwin and his contem-poraries. Darwin himself famously labeled the Cretaceous appearance of angiosperms an "abominable mystery". Since Darwin's time much more has been learnt about the pattern of angiosperm diversifi-cation and some aspects of his "mystery" now seem much less problematic. The discovery and study of fossil flowers and other reproductive organs from the Cretaceous has played an important role in recent progress and has provided unexpected insights into the early phases of angiosperm diversi-fication. The new picture that continues to emerge indicates that angiosperms were diverse already by the Late Barremian-Early Aptian, albeit represented by extinct lineages and a limited selection of extant lineages related particularly to ANITA-grade angiosperms, Chloranthaceae and basal mono-cots. This phylogenetic diversity is strikingly different from the much more modern appearance that characterizes Late Cretaceous and younger floras. Early in the diversification the occurrence of an-giosperms was probably patchy, and the earliest angiosperms appear mainly to have been insect pol-linated, herbaceous or shrubby, plants of low stature and low pollen production. Together with ferns they may have formed the ground cover in open areas or the understory in open-forests dominated by xeromorphic conifers and plants related to Bennettitales, Erdtmanithecales and Gnetales. Systematic assignments, together with the general morphology of the vegetative remains of early angiosperms, also suggest that the aquatic habit was established at a very early stage in angiosperm history.
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