The extraordinary diversity of angiosperms is the ultimate outcome of the interplay of speciation and extinction, which determine the net diversification of different lineages. We document the temporal trends of angiosperm diversification rates during their early history. Absolute diversification rates were estimated for order-level clades using ages derived from relaxed molecular clock analyses that included or excluded a maximal constraint to angiosperm age. Diversification rates for angiosperms as a whole ranged from 0.0781 to 0.0909 net speciation events per million years, with dates from the constrained analysis. Diversification through time plots show an inverse relationship between clade age and rate, where the younger clades tend to have the highest rates. Angiosperm diversity is found to have mixed origins: slightly less than half of the living species belong to lineages with low to moderate diversification rates, which appeared between 130 and 102 Mya (Barremian-uppermost Albian; Lower Cretaceous). Slightly over half of the living species belong to lineages with moderate to high diversification rates, which appeared between 102 and 77 Mya (Cenomanian-mid Campanian; Upper Cretaceous). Terminal lineages leading to living angiosperm species, however, may have originated soon or long after the phylogenetic differentiation of the clade to which they belong.

Angiosperm diversification through time.

Cretaceous angiosperm flowers: Innovation and evolution in plant reproduction

• Plants have utterly transformed the planet, but testing hypotheses of causality requires a reliable time-scale for plant evolution. While clock methods have been extensively developed, less attention has been paid to the correct interpretation and appropriate implementation of fossil data. • We constructed 17 calibrations, consisting of minimum constraints and soft maximum constraints, for divergences between model representatives of the major land plant lineages. Using a data set of seven plastid genes, we performed a cross-validation analysis to determine the consistency of the calibrations. Six molecular clock analyses were then conducted, one with the original calibrations, and others exploring the impact on divergence estimates of changing maxima at basal nodes, and prior probability densities within calibrations. • Cross-validation highlighted Tracheophyta and Euphyllophyta calibrations as inconsistent, either because their soft maxima were overly conservative or because of undetected rate variation. Molecular clock analyses yielded estimates ranging from 568-815 million yr before present (Ma) for crown embryophytes and from 175-240 Ma for crown angiosperms. • We reject both a post-Jurassic origin of angiosperms and a post-Cambrian origin of land plants. Our analyses also suggest that the establishment of the major embryophyte lineages occurred at a much slower tempo than suggested in most previous studies. These conclusions are entirely compatible with current palaeobotanical data, although not necessarily with their interpretation by palaeobotanists.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.2011.03794.x

Establishing a time-scale for plant evolution

UNLABELLED PREMISE OF THE STUDY Land plants play an essential role in the evolution of terrestrial life. Their time of origin and diversification is fundamental to understanding the evolution of life on land. We investigated the timing and the rate of molecular evolution of land plants, evaluating the effects of different types of molecular data, including temporal information from fossils, and using different molecular clock methods. • METHODS Ages and absolute rates were estimated independently with two substitutionally different data sets: a highly conserved 4-gene data set and matK, a fast-evolving gene. The vascular plant backbone and the crown nodes of all major lineages were calibrated with fossil-derived ages. Dates and absolute rates were estimated while including or excluding the calibrations and using two relaxed clocks that differ in their implementation of temporal autocorrelation. • KEY RESULTS Land plants diverged from streptophyte alga 912 (870-962) million years ago (Mya) but diversified into living lineages 475 (471-480) Mya. Ages estimated for all major land-plant lineages agree with their fossil record, except for angiosperms. Different genes estimated very similar ages and correlated absolute rates across the tree. Excluding calibrations resulted in the greatest age differences. Different relaxed clocks provided similar ages, but different and uncorrelated absolute rates. • CONCLUSIONS Whole-genome rate accelerations or decelerations may underlie the similar ages and correlated absolute rates estimated with different genes. We suggest that pronounced substitution rate changes around the angiosperm crown node may represent a challenge for relaxed clocks to model adequately.

Land plant evolutionary timeline: Gene effects are secondary to fossil constraints in relaxed clock estimation of age and substitution rates

Hilton J. (School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK) and R. M. Bateman (Natural History Museum, Cromwell Road, London, SW7 5BD, UK). Pteridosperms are the backbone of seed-plant phylogeny. J. Torrey Bot. Soc. 133: 119–168. 2006.— Using Doyle (1996) as a starting point, we compiled a morphological cladistic matrix of 54 coded taxa (31 wholly extinct, and 23 at least partly extant) and 102 informative characters in order to explore relationships among gymnosperms in general and pteridosperms in particular. Our core analysis omitted six supplementary fossil taxa and yielded 21 most-parsimonious trees that generated two polytomies in the strict consensus tree, both among pteridosperms; the first affected several hydraspermans, and the second affected the three peltasperm/ corystosperm taxa analyzed. The resulting topology broadly resembled topologies generated during previous morphological cladistic analyses that combined subs...

https://bioone.org/journals/the-journal-of-the-torrey-botanical-society/volume-133/issue-1/1095-5674(2006)133%5b119%3aPATBOS%5d2.0.CO%3b2/Pteridosperms-are-the-backbone-of-seed-plant-phylogeny1/10.3159/1095-5674(2006)133[119:PATBOS]2.0.CO;2.pdf

Pteridosperms are the backbone of seed-plant phylogeny

An Early Cretaceous angiosperm, Sinocarpus decussatus gen. et sp. nov., is described from the Yixian Formation in Liaoning, China, based on an infructescence fragment. It is probably ebracteate, consisting of one terminal fruit and two pairs of pedicellate lateral fruits arranged decussately. Carpels are probably borne on a small convex receptacle. There are no distinct remnants of a perianth although fragments observed at the base of immature fruits may represent perianth parts. No remnants of androecial parts have been observed, and it is unknown whether the flowers were unisexual or bisexual. The basally syncarpous ovary is superior and composed of 3 or 4 carpels. Each carpel contains about 10 anatropous ovules/seeds borne along the linear placentae. Seeds are flattened and embedded in a thick amorphous material. The character combination of Sinocarpus indicates a systematic position among the basal grade of eudicots or the basal core eudicots, and particularly shows similarities to extant Ranunculaceae, Buxaceae, and Myrothamnaceae, but based on the available data the fossil cannot unambiguously be placed in any modern family.

Sinocarpus decussatus gen. et sp. nov., a new angiosperm with basally syncarpous fruits from the Yixian Formation of Northeast China

Typical angiosperm dicot leaves are discovered closely associated with reproductive organs of Sinocarpus decussatus from the Yixian Formation, NE China. Leaves are of first rank, small, with fine texture, and with distinct petiole and lamina. Venation pattern is craspedodromous, of at least three discrete orders of veins irregularly arranged. Leaf margin is serrate, with glandular teeth of chloranthoid type. The new Sinocarpus material is better preserved and more complete than the type specimen. It yields support for previous interpretations of reproductive characters and shows that the inflorescences were compound, perhaps combining alternate and opposite phyllotaxis, and that seeds were arranged in two rows, each row with about ten seeds. While these new reproductive characters do not provide further resolution to the systematic assignment of Sinocarpus, the associated leaves, believed to be from the same plant, support previous interpretation of Sinocarpus as a basal eudicot, and particularly close to Ranunculales.

Q. Leng

Papers

Sinocarpus decussatus gen. et sp. nov., a new angiosperm with basally syncarpous fruits from the Yixian Formation of Northeast China

Angiosperm leaves associated with Sinocarpus infructescences from the Yixian Formation (mid-Early Cretaceous) of NE China