Editing Saxifragales (section)

=== Biogeography and evolution ===

[[Genetic divergence|Diversification]] among Saxifragales was rapid, with the extensive [[fossil]] record{{sfn|Hermsen et al|2006}}{{sfn|Hermsen et al|2003}}{{sfn|Pigg et al|2004}}{{sfn|Hernández-Castillo|Cevallos-Ferriz|1999}}{{sfn|Crane|1989}}{{sfn|Endress|1989}} indicating that the order was more [[Biodiversity|diverse]] and more [[Cosmopolitan distribution|widespread]] than an examination of the [[Extant taxon|extant]] members suggests, with considerable [[phenotypic]] diversity occurring early.{{sfn|Casas et al|2016}} The earliest fossil evidence is found in the [[Turonian]]-[[Campanian]] (late Cretaceous), suggesting a minimum age of 89.5&nbsp;[[Myr]]. However, molecular [[divergence time estimation]] suggest an earlier time of 102–108&nbsp;Myr, into the early Cretaceous, for the [[Crown group|crown]] and [[stem group]]s respectively. Within the order Saxifragales, the molecular data imply a very rapid initial diversification time of about 6–8&nbsp;Myr, between 112 and 120&nbsp;Myr, with major lineages appearing within 3–6&nbsp;Myr.{{sfn|Jian et al|2008}}{{sfn|Soltis et al|2013}}{{sfn|Li et al|2019}}

The ancestral state appears to be woody, as in Peridiscaceae and the woody clade, but is also ancestral to Grossulariaceae. A number of independent transitions to a herbaceous habit occurred in the ancestors of Crassulaceae, Saxifragaceae and the base of the Haloragaceae-Penthoraceae clade (the other two families in Haloragaceae ''s.l.'' remaining woody), while other taxa reverted to a woody habit, especially Crassulaceae. Most of Saxifragales have a superior [[Ovary (botany)|ovary]], but some families show frequent transition with inferior or subinferior position, particularly Saxifragaceae and to a lesser extent Hamamelidaceae. Almost all Grossulariaceae have an inferior ovary. The ancestral [[carpel]] number is two, with transition to higher numbers, such as four in Haloragaceae ''s.l.'' and Peridiscaceae with five in Penthoraceae. The ancestral carpel number for Crassulaceae is five, decreasing to four in ''[[Kalanchoe]]'', where it is synapomorphic for the genus, though the most frequent transition in this family is 6–10, but only where [[stamen]] number is increased above five. Some [[Macaronesian]] taxa (Aeonieae) have 8–12, with up to 32 carpels for ''[[Aeonium]]''.{{sfn|Soltis et al|2013}}

The ancestral petal number is five, with three major transitions; 5 to 0, 5 to 4, 5 to 6–10. Increased petal number is seen in Paeoniaceae and Crassulaceae, particularly where stamen number is also increased. Cercidiphyllum + Daphniphyllum, Chrysosplenium and ''[[Altingia]]'' are examples of the complete loss of petals. The ancestral stamen:petal ratio is 1, with transitions characterising several clades, e.g. Paeonicaceae+woody clade >2, Crassulaceae 2 (but ''[[Crassula]]'' 1). Overall there has been a decrease over evolution, but independent of a decrease in petal number, so that it is the stamen number that has decreased.{{sfn|Soltis et al|2013}} The ancestral habitat appears to be forests, followed by early diversification into desert and aquatic habitats, with shrubland the most recent colonization.{{sfn|Casas et al|2016}}

Species diversification was rapid following a transition from a warmer, wetter Earth in the [[Eocene]] (56–40&nbsp;Myr) to early [[Miocene]] (23–16&nbsp;Myr), to the cooler drier conditions of the mid-Miocene (16–12&nbsp;Myr). However, this appears to not have coincided with ecological and phenotypic evolution, which are themselves correlated. There is a clear lag, whereby increase in species diversification was followed later by increases in niche and phenotypic lability.{{sfn|Folk et al|2019}}