We present a phylogenetic dating of asterids, based on a 111-taxon tree representing all major groups and orders and 83 of the 102 families of asterids, with an underlying data set comprising six chloroplast DNA markers totaling 9914 positions. Phylogenetic dating was done with semiparametric rate smoothing by penalized likelihood. Confidence intervals were calculated by bootstrapping. Six reference fossils were used for calibration. To explore the effects of various sources of error, we repeated the analyses with alternative dating methods (nonparametric rate smoothing and the Langley-Fitch clock-based method), alternative tree topologies, reduced taxon sampling (22 of the 111 taxa deleted), partitioning the data into three genes and three noncoding regions, and calibrating with single reference fossils. The analyses with alternative topologies, reduced taxon sampling, and coding versus noncoding sequences all yielded small or in some cases no deviations. The choice of method influenced the age estimates of a few nodes considerably. Calibration with reference fossils is a critical issue, and use of single reference fossils yielded different results depending on the fossil. The bootstrap confidence intervals were generally small. Our results show that asterids and their major subgroups euasterids, campanulids, and lamiids diversified during the Early Cretaceous. Cornales, Ericales, and Aquifoliales also have crown node ages from the Early Cretaceous. Dipsacales and Solanales are from the Mid-Cretaceous, the other orders of core campanulids and core lamiids from the Late Cretaceous. The considerable diversity exhibited by asterids almost from their first appearance in the fossil record also supports an origin and first phase of diversification in the Early Cretaceous.

中文翻译：

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Asterid 开花植物的分子系统发育定年显示早白垩世的多样化

我们基于代表所有主要类群和目以及 102 个 asterids 家族中的 83 个的 111 个分类单元树提出了 asterids 的系统发育年代，其基础数据集包括总共 9914 个位置的六个叶绿体 DNA 标记。系统发育定年是通过惩罚似然的半参数率平滑完成的。通过自举法计算置信区间。六个参考化石用于校准。为了探索各种误差来源的影响，我们使用替代测年方法（非参数平滑和基于兰利-费奇时钟的方法）、替代树拓扑、减少分类单元采样（删除 111 个分类单元中的 22 个）、分区重复分析将数据分为三个基因和三个非编码区域，并使用单个参考化石进行校准。具有替代拓扑的分析，减少的分类单元抽样，编码与非编码序列都产生很小的偏差或在某些情况下没有偏差。方法的选择极大地影响了一些节点的年龄估计。使用参考化石进行校准是一个关键问题，根据化石使用单一参考化石会产生不同的结果。自举置信区间通常很小。我们的研究结果表明，在早白垩世，asterids 及其主要亚群euasterids、campanulids 和lamiids 发生了多样化。Cornales、Ericales 和 Aquifoliales 也有早白垩世的冠节点年龄。Dipsacales 和 Solanales 来自中白垩世，其他的核心钟形目和核心层形目来自晚白垩世。