How the timing of a group divergence is ultimately resolved depends on correctly
inferring its relationship to other groups, and this is probably not the case for some of the
Figure 8.6 Chronogram calibrated against the geological timescale (Harland et al. 1990) focusing on
asterids. Fossil-based estimates extracted from Magallón et al. (1999) are indicated with thick bars.
The chronogram is based on the analysis using ACCTRAN optimization for calculating branch
lengths, and has been generalized, usually down to family level, to facilitate a graphical comparison
between our molecular-based estimates and the fossil-based estimates (Magallón et al. 1999). Non-
generalized chronograms, indicating age estimates for all included taxa, have been presented
elsewhere (Wikström et al. 2001), and node numbers correspond to those given there. With few
exceptions (taxa marked with ) taxon names follow those used by Soltis et al. (1999), and arrows
indicate nodes that received less than 50 per cent jackknife support in their phylogenetic analyses
(Soltis et al. 1999, 2000). Taxa marked with have been generalized and named to correspond with
the usage of Magallón et al. (1999).
ANGIOSPERM DIVERGENCE 163