Editing Saxifragales (section)

=== Subdivision ===

The first APG classification (1998) placed 13 families within the order Saxifragales:{{sfn|APG I|1998}} 
{{div col|colwidth=160px}}
* [[Altingiaceae]] 
* [[Cercidiphyllaceae]] 
* [[Crassulaceae]] 
* [[Daphniphyllaceae]]
* [[Grossulariaceae]]
* [[Haloragaceae]]
* [[Hamamelidaceae]]
* [[Iteaceae]]
* [[Paeoniaceae]]
* [[Penthoraceae]]
* [[Pterostemonaceae]]
* [[Saxifragaceae]]
* [[Tetracarpaeaceae]]
{{div col end}}
This was subsequently revised to 15, in the fourth version (2016).{{sfn|APG IV|2016}} The Saxifragales families have been grouped into a number of informally named suprafamilial subclades, with the exception of the [[basal split]] of Peridiscaceae, which thus forms a [[sister group]] with the rest of Saxifragales. The two major ones are (Paeoniaceae + the woody clade of primarily woody families) and the "core" Saxifragales (i.e. the primarily herbaceous families), with the latter subdivided into two further subclades, (Haloragaceae ''sensu lato'' + Crassulaceae) and the Saxifragaceae alliance.{{sfn|Soltis et al|2013}}

In the clade Haloragaceae ''sensu lato'' ''(s.l.)'' + Crassulaceae the genera constituting Haloragaceae ''s.l.'' are all small, and APG II (2003) proposed merging them into a single larger Haloragaceae ''s.l.'', but transferred ''[[Aphanopetalum]]'' from [[Cunoniaceae]] to this group.{{sfn|APG II|2003}} The Saxifragaceae alliance represents Saxifragaceae together with a number of woody members of the traditional Saxifragaceae ''sensu'' Engler (1930).{{sfn|Engler|1930}} Within this, APG II (2003) proposed placing the two species of ''[[Pterostemon]]'' that constitute Pterostemonaceae within [[Iteaceae]], and all subsequent versions have maintained this practice.{{sfn|APG II|2003}} Thus Saxifragales ''sensu'' APG II consisted of only 10 families. The third version (2009) added [[Peridiscaceae]] (from [[Malpighiales]]), as sister to all other families, but re-expanded Haloragaceae to provide for a narrower circumscription, Haloragaceae ''sensu stricto'' (''s.s.''), to give a total of 14 families. APG IV (2016) added the parasitic family Cynomoriaceae to provide a total of 15 families, although its placement within the order remained unclear.{{sfn|Bellot et al|2016}}{{sfn|APG IV|2016}}

Of the 15 families included in APG IV, the basal divergence Peridiscaceae underwent radical shifting and recircumscription from 2003 to 2009. Originally, it consisted of two closely related genera, ''Peridiscus'' and ''Whittonia''. The [[APG II]] system placed the family in [[Malpighiales]], based on a [[DNA sequence]] for the [[RuBisCO|''rbcL'']] [[gene]] from ''Whittonia''. This sequence turned out to be not from ''Whittonia'', but from other plants whose [[DNA]] had contaminated the sample.{{sfn|Davis|Chase|2004}} After placement in Saxifragales, it was expanded to include ''[[Soyauxia]]'' in 2007,{{sfn|Soltis et al|2007}} and ''[[Medusandra]]'' in 2009.{{sfn|Wurdack|Davis|2009}}

In the first of the subclades of the remaining Saxifragales, Paeoniaceae possesses many [[autapomorphy|unique]] features and its taxonomic position was controversial for a long time,{{sfn|Tamura|2007}} and ''[[Peony|Paeonia]]'' was placed in [[Ranunculales]], close to ''[[Glaucidium (plant)|Glaucidium]]'',{{sfn|Mabberley|2008}}{{sfn|Halda|Waddick|2010}} prior to transfer to Saxifragales as sister to the woody clade.{{sfn|Jian et al|2008}}{{sfn|Wang et al |2009a}}

In the woody clade, the genus ''[[Liquidambar]]'' was included in Hamamelidaceae until [[molecular phylogenetic]] studies showed that its inclusion might make Hamamelidaceae [[Paraphyly|paraphyletic]], and was segregated as a separate monotypic family, Altingiaceae in 2008.{{sfn|Jian et al|2008}} Cercidiphyllaceae was for a long time associated with Hamamelidaceae and [[Trochodendraceae]] and was often thought to be closer to the latter,{{sfn|Endress|1986}} which is now in the basal [[eudicot]] order [[Trochodendrales]].{{sfn|Worberg et al|2007}} ''Daphniphyllum'' was always thought to have an anomalous combination of characters{{sfn|Tseng-Chieng|1965}}{{sfn|Tseng-Chieng|1965}} and was placed in several different orders before molecular phylogenetic analysis showed it to belong to Saxifragales.{{sfn|Kubitzki|2007b}}

In the core Saxifragales, Crassulaceae{{sfn|Thiede |Eggli|2007}} and Tetracarpaeaceae{{sfn|Hils et al|1988}} have been associated with Saxifragaceae, while ''Penthorum'' has been associated both with Crassulaceae and Saxifragaceae,{{sfn|Thiede|2007}} before being placed here. ''[[Aphanopetalum]]'' was often placed in [[Cunoniaceae]], a family in [[Oxalidales]], even though there were good reasons to put it in Saxifragales,{{sfn|Dickison et al|1994}} and it was subsequently transferred.{{sfn|Bradford|Fortune-Hopkins|Barnes|2004}} Haloragaceae was included in [[Myrtales]],{{sfn|Kubitzki|2007c}} before being placed in Saxifragales.{{sfn|Moody | Les |2007}}

The other "core" group, the Saxifragaceae alliance comprises four families: Pterostemonaceae, Iteaceae, Grossulariaceae, and Saxifragaceae,{{sfn|Jian et al|2008}} which have long been known to be related to each other, but the [[Circumscription (taxonomy)|circumscription]] of Saxifragaceae has been much reduced and Pterostemonaceae submerged as ''[[Pterostemon]]'' in Iteaceae.{{sfn|Soltis et al|2001}}

Most of the families are [[monogeneric]]. ''Choristylis'' is now considered a synonym of [[Itea (plant)|''Itea'']], but the addition of ''[[Pterostemon]]'', gives Iteaceae two genera.{{sfn|Kubitzki|2007d}} ''[[Liquidambar]]'' and ''[[Semiliquidambar]]'' are also submerged into ''[[Altingia]]'', making Altingiaceae monogeneric.{{sfn|Ickert-Bond|Wen|2006}}{{sfn|Ickert-Bond |Wen|2013}} About 95% of the species are in five families: [[Crassulaceae]] (1400), [[Saxifragaceae]]  (500), [[Grossulariaceae]] (150–200), [[Haloragaceae]] (150), and [[Hamamelidaceae]] (100).{{sfn|Stevens|2019}}{{sfn|Jian et al|2008}}{{sfn|Kubitzki|2007a|pp=15–18}}

The relationships of the Saxifragales families to each other is shown in the following [[cladogram]]. The [[phylogeny]] in this cladogram still has some uncertainty as to the exact relationships, and the phylogenetic tree is subject to further revision.{{sfn|Dong et al|2018}}{{sfn|Ding et al|2019}} [[Cynomoriaceae]], previously placed in [[Santales]] or [[Rosales]] is included in Saxifragales, but unplaced within it. Li et al. (2019) have slightly different relationships, and also place Cynomoriaceae as the first branch in the Crassulaceae+Haloragaceae ''s.l.'' tree, i.e. as sister to those two families.{{sfn|Li et al|2019}} The number of genera in each family is shown in parentheses:
{{cladogram
|title= Cladogram of Saxifragales families{{sfn|APG IV|2016}}{{sfn|Stevens|2019}}{{sfn|Jian et al|2008}}
|caption=100% [[maximum likelihood]] [[Bootstrapping (statistics)|bootstrap support]] except where labeled with bootstrap percentage<br/>Monogeneric families are represented by genus names, otherwise the number of genera is in (parentheses)<br/>[[Cynomorium]] (Cynomoriaceae) remains unplaced within this tree
|align=left
|cladogram=
{{clade | style=font-size:100%;line-height:120%;width:700px;
|label1='''Saxifragales'''
|1={{clade
   |1=[[Peridiscaceae]] (4)
   |label2=97
   |2={{clade
      |label1=
      |1={{clade
         |1=''[[Peony|Paeonia]]'' (Paeoniaceae)
         |label2=woody clade
         |2={{clade
            |1=''[[Liquidambar]]'' (Altingiaceae)
            |label2=69
            |2={{clade
               |label1=98
               |1=[[Hamamelidaceae]] (27)
               |label2=95
               |2={{clade
                  |1=''[[Cercidiphyllum]]'' (Cercidiphyllaceae)
                  |2=''[[Daphniphyllum]]'' (Daphniphyllaceae)
                  }}
               }}
            }}
         }}
      |label2=core Saxifragales
      |2={{clade
         |1={{clade
            |1=[[Crassulaceae]] (34)
            |label2=Haloragaceae''s.l.''
            |2={{clade
               |1=''[[Aphanopetalum]]'' (Aphanopetalaceae)
               |2={{clade
                  |1=''[[Tetracarpaea]]'' (Tetracarpaeaceae)
                  |2={{clade
                     |1=''[[Penthorum]]'' (Penthoraceae)
                     |2=[[Haloragaceae]] ''s.s.'' (8)
                     }}
                  }}
               }}
            }}
         |label2=Saxifragaceae alliance
         |2={{clade
            |1={{clade
               |1=[[Iteaceae]] (including [[Pterostemonaceae]]) (2)
               }}
            |2={{clade
               |1=''[[Ribes]]'' (Grossulariaceae) 
               |2=[[Saxifragaceae]] (33)
               }}
            }}
         }}
      }}
   }}
}}

}}

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