Editing Saxifragaceae (section)

== Taxonomy ==
Saxifragaceae has long been considered in a pivotal position in the evolution of angiosperm lineage, located in an ancestral "Saxifragalean stock". Historically the Saxifragaceae have included many very [[Morphology (biology)|morphologically]] disparate [[taxa]] in systems based on morphology alone, and has been very difficult to classify and characterize [[phenotypically]]. Consequently many different classifications have been published, differing considerably in both the relationship of the family to other angiosperms, and its internal structure, for instance the systems of [[Arthur Cronquist|Cronquist]] (1981), [[Rolf Dahlgren|Dahlgren]] (1983), [[Adolf Engler|Engler]] (1890), [[John Hutchinson (botanist)|Hutchinson]] (1973), Schulze-Menz (1964),{{sfn|Schulze-Menz|1964}} [[Takhtajan]] (1980) and [[Robert F Thorne|Thorne]] (1992) (''for a history, see {{harvtxt|Morgan|Soltis|1993}}''. In its broadest [[Circumscription (taxonomy)|circumscription]], it included 17 subfamilies.{{sfn|Schulze-Menz|1964}} This construction is referred to as Saxifragaceae ''[[sensu lato]]'' (''s.l.''). Within those subfamilies, the large majority of genera (30) were located within subfamily Saxifragoideae, the core group, with all but two of the remainder only having 1-3 genera.{{sfn|Morgan|Soltis|1993}}{{sfn|Soltis|Soltis|1997}}

The circumscription of the family has changed considerably in recent years, in large part due to [[molecular phylogenetic]] work showing the family ''s.l.'' to be [[polyphyletic]], and probably represents the most extreme example, with at least 10 evolutionary lines. Consequently the circumscription has been considerably reduced, with many of the subfamilies being either elevated to separate families, or placed as components of other families, often quite distant. For instance subfamily Parnassioideae was raised to the level of family [[Parnassiaceae]], and eventually a subfamily of [[Celastraceae]] (order [[Celastrales]]). Similarly the Hydrangoideae is now the family [[Hydrangeaceae]] (order [[Cornales]]).{{sfn|Morgan|Soltis|1993}}{{sfn|APG IV|2016}}

The reduced Saxifragaceae is distinguished by being referred to as Saxifragaceae ''sensu stricto'' (''s.s.''), corresponding to the Saxifragoideae a natural monophyletic group.{{sfn|Soltis et al|1993}} Historically, the Saxifragaceae has been placed in either the [[Order (biology)|order]]s [[Rosales]] or [[Saxifragales]]. This reduced Saxifragaceae, corresponding to subfamily Saxifragoideae and its 30 genera, is now placed within the Saxifragales. There, with three other subfamilies (Ribesoideaee, Iteoideae and Pterostemonoideae) it forms the Saxifragaceae alliance, while Penthoroideae and Tetracarpaeoideae are closely related within the core Saxifragales as shown in the [[cladogram]]. The remaining subfamilies are all transferred to more distant orders within the [[rosid]] and [[asterid]] clades.{{sfn|Deng et al|2015}}{{sfn|Morgan|Soltis|1993}}{{sfn|APG IV|2016}}
{{cladogram
|title= Cladogram I: Saxifragales families{{sfn|Jian et al|2008}}{{sfn|Stevens|2019}}{{sfn|APG IV|2016}}
|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''' ''s.s.'' (33)
               }}
            }}
         }}
      }}
   }}
}}

}}

{{Clear}}

=== Subdivision ===
[[File:American Alumroot Heuchera americana 'Garnet' Stalk 2448px.JPG|thumb|upright|''[[Heuchera americana]]''|alt=Flower stalk of Heuchera americana]]
[[File:Rodgersia podophylla 4587.jpg|thumb|upright|''[[Rodgersia podophylla]]''|alt=Flowers of Rodgersia podophylla]]
[[File:Saxifraga merkii var idsuroei s2.jpg|thumb|upright|''[[Micranthes merkii]]''|alt=Flowers of Micranthes merkii]]

Numerous attempts have been made to subdivide Saxifragoideae (Saxifragaceae ''s.s.''). These have included dividing the family by the placentation of the ovules, as either parietal (e.g. ''Heuchera'') or axile (e.g. ''Saxifraga''). None of these has been supported by molecular data.{{sfn|Byng|2014}}{{sfn|Soltis et al|1993}}

[[molecular phylogenetic|Molecular data]] indicate that the family can be considered as a number of informal [[clades]], with two main lineages, saxifragoids and heucheroids and further subdivision of heucheroids into nine subclades or groups:{{sfn|Soltis et al|1993}}{{sfn|Deng et al|2015}}{{sfn|Byng|2014}}
;Clades (Genera (Species))
* Saxifragoids (''[[Saxifraga]]'' (370))
* Heucheroids (remaining genera):
** Leptarrhena (''[[Leptarrhena]]'' (1), ''[[Tanakaea]]'' (1))
** Saniculiphyllum (''[[Saniculiphyllum]]'' (1))
** Boykinia (''[[Boykinia]] (6), [[Bolandra]] (2), [[Hieronymusia]] (1), [[Jepsonia]] (3), [[Sullivantia]] (3), [[Suksdorfia]]'' (2), ''[[Telesonix]]'' (2))
** Astilbe (''[[Astilbe]]'' (23), ''[[Saxifragopsis]]'' (1))
** Heuchera ([[Heuchera]] (36), ''[[Bensoniella]] (1), [[Conimitella]] (1), [[Elmera]] (1), [[Lithophragma]] (10), [[Mitella]] (20), [[Tellima]] (1), [[Tiarella]]'' (3), ''[[Tolmiea]]'' (1))
** Cascadia (''[[Saxifraga|Cascadia]]'' (1), ''[[Saxifragodes]]'' (1))
** Darmera (''[[Darmera]] (1), [[Astilboides]] (1), [[Bergenia]] (10), [[Mukdenia]] (1), [[Oresitrophe]]'' (1), ''[[Rodgersia]]'' (5))
** Peltoboykinia (''[[Peltoboykinia]]'' (1), ''[[Chrysosplenium]]'' (55))
** Micranthes (''[[Micranthes]]'' (70))

The clades and subclades are related as shown in the cladogram:{{sfn|Deng et al|2015}}
{{cladogram|title=Cladogram II: Infrafamilial structure of Saxifragaceae
|caption=Diversification time in Mya underneath group names
|align=left
|cladogram=
{{clade|style=font-size:90%;line-height:100%
|label1='''Saxifragaceae'''
|sublabel1=38
|1={{clade
    |label1=Saxifragoids
    |sublabel1=30
    |1=''Saxifraga''
    |label2=Heucheroids
    |sublabel2=31
    |2={{clade 
      |1={{clade
     |sublabel1=20
        |1={{clade
          |sublabel1=18
          |1={{clade
             |sublabel1=8
             |1=Leptarrhena
             |sublabel2=16
             |2={{clade
               |1=''Saniculiphyllum''
               |sublabel2=11
               |2=Boykinia
                }}
             }}
             |sublabel2=14
             |2=Astilbe
             }}
         |2={{clade
          |1={{clade
           |sublabel1=7
           |1=Heuchera
           |sublabel2=29
           |2={{clade
           |1={{clade
                |sublabel1=19
                |1=Cascadia
                |sublabel2=10
                |2=Darmera
                }}
             |sublabel2=27
             |2={{clade
                |sublabel1=23
                |1=Peltoboykinia
                |sublabel2=15
                |2=''Micranthes''
                }}
           }}
}}
}}
}}
}} 
}}
}}
}}
{{Clear}}

==== Genera ====
{{main|List of Saxifragaceae genera}}
Saxifragaceae ''s.s.'' has about 33–35 genera and about 640 species. About half of the genera (18 of 33) are [[monotypic]], but ''Saxifraga'' has about 400 species, and has generally been divided into sections.{{sfn|Soltis et al|1993}}{{sfn|Christenhusz|Byng|2016}}{{sfn|Christenhusz et al|2017}}{{sfn|Deng et al|2015}}

=== Evolution and biogeography ===

The [[crown group]] of Saxifragaceae [[Genetic divergence|diversified]] at about 38&nbsp;[[Mya (unit)|Mya]] (Mid–Late [[Eocene]]), with the two main lineages diversifying arising at about 30&nbsp;Mya (Late Miocene/Early [[Oligocene]]). The present day heucheroid diversity dates later than the Miocene (''see sublabels in Cladogram II''). Ancestral Saxafragaceae emerged in either East Asia or Western North America, with subsequent dispersal West to Europe and south to South America. From the Eocene to the late Miocene these ancestral land masses were joined by the [[Bering Land Bridge]] facilitating plant migration.{{sfn|Deng et al|2015}}

=== Etymology ===

The family and type genus name are derived from the two Latin words ''saxum'' (rock), and ''frango'' (to break), but the exact origin is unknown, although surmised to refer to either growing in crevices in rocks or medicinal use for [[kidney stones]].{{sfn|Christenhusz et al|2017}}