Saxifragaceaeis a family ofherbaceousperennialflowering plants,within thecore eudicotorderSaxifragales. Thetaxonomyof the family has been greatly revised and the scope much reduced in the era ofmolecular phylogeneticanalysis. The family is divided into tenclades,with about 640 known species in about 35 acceptedgenera.About half of these consist of a single species, but about 400 of the species are in the type genusSaxifraga.The family is predominantly distributed in the northern hemisphere, but also in the Andes in South America.
| Saxifragaceae | |
|---|---|
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| Tiarella (Foamflower) | |
Scientific classification
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| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Order: | Saxifragales |
| Family: | Saxifragaceae Juss. |
| Type genus | |
| Saxifraga | |
| Clades | |
|
See text | |
| |
| The range of Saxifragaceae | |
Description
editThis sectionmay be too technical for most readers to understand.(August 2020) |
Species areherbaceousperennials(rarelyannualorbiennial), sometimessucculentorxerophytic,often with perennatingrhizomes.Theleavesare usually basally aggregated in alternate rosettes, sometimes oninflorescencestems. They are usually simple, rarely pinnately or palmately compound. Their margins may be entire, deeply lobed, cleft, crenate or dentate and petiolate with stipules.[1][2]
The inflorescences are bracteate racemes or cymes. Theflowersarehermaphroditic(bisexual), rarely unisexual (androdioecious),actinomorphic(rarelyzygomorphic). Theperianthis placed on a hypanthium that may be free or may be partly fused with theovary(which is then semi-inferior). There are usually fivesepals,but there may be three to ten, fused with the hypanthium, occasionally petaloid. Thepetalsare clawed, sometimes cleft at the tip or finely dissected. Flowers have five to tenstamens,free and opposite the petals, with the anthers usually basifixed and opening by lengthwise slits. The ovary is inferior to semi-inferior with two (sometimes three)carpelsusually fused at the base, sometimes free, each topped with stylodium and capitate stigma. Theovulesare few to many, with axile or parietal placentation and two to threestyles.Thefruitis usually a septicidal capsule or follicle, with numerous smallseeds.[1][2]
Taxonomy
editSaxifragaceae 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 verymorphologicallydisparatetaxain systems based on morphology alone, and has been very difficult to classify and characterizephenotypically.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 ofCronquist(1981),Dahlgren(1983),Engler(1890),Hutchinson(1973), Schulze-Menz (1964),[3]Takhtajan(1980) andThorne(1992) (for a history, seeMorgan & Soltis (1993).In its broadestcircumscription,it included 17 subfamilies.[3]This construction is referred to as Saxifragaceaesensu 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.[4][5]
The circumscription of the family has changed considerably in recent years, in large part due tomolecular phylogeneticwork showing the familys.l.to bepolyphyletic,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 familyParnassiaceae,and eventually a subfamily ofCelastraceae(orderCelastrales). Similarly the Hydrangoideae is now the familyHydrangeaceae(orderCornales).[4][6]
The reduced Saxifragaceae is distinguished by being referred to as Saxifragaceaesensu stricto(s.s.), corresponding to the Saxifragoideae a natural monophyletic group.[7]Historically, the Saxifragaceae has been placed in either theordersRosalesorSaxifragales.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 thecladogram.The remaining subfamilies are all transferred to more distant orders within therosidandasteridclades.[8][4][6]
| Cladogram I: Saxifragales families[9][10][6] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| 100%maximum likelihoodbootstrap supportexcept where labeled with bootstrap percentage Monogeneric families are represented by genus names, otherwise the number of genera is in (parentheses) Cynomorium(Cynomoriaceae) remains unplaced within this tree |
Subdivision
edit
Numerous attempts have been made to subdivide Saxifragoideae (Saxifragaceaes.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.[1][7]
Molecular dataindicate that the family can be considered as a number of informalclades,with two main lineages, saxifragoids and heucheroids and further subdivision of heucheroids into nine subclades or groups:[7][8][1]
- 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 (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:[8]
| Cladogram II: Infrafamilial structure of Saxifragaceae | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Diversification time in Mya underneath group names |
Genera
editSaxifragaceaes.s.has about 33–35 genera and about 640 species. About half of the genera (18 of 33) aremonotypic,butSaxifragahas about 400 species, and has generally been divided into sections.[7][11][2][8]
Evolution and biogeography
editThecrown groupof Saxifragaceaediversifiedat about 38Mya(Mid–LateEocene), with the two main lineages diversifying arising at about 30 Mya (Late Miocene/EarlyOligocene). 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 theBering Land Bridgefacilitating plant migration.[8]
Etymology
editThe family and type genus name are derived from the two Latin wordssaxum(rock), andfrango(to break), but the exact origin is unknown, although surmised to refer to either growing in crevices in rocks or medicinal use forkidney stones.[2]
Distribution and habitat
editPrimarily Northern hemisphere temperate and arctic regions, and also tropical montane, including the Americas, Europe, North Africa (including montane Ethiopia) and temperate and subtropical Asia toLuzonand New Guinea. In the Americas it extends south to central Mexico and the Andes toTierra del Fuego.Centres of diversityare western N America, East Asia and the Himalayas. The largest concentration of genera are in the Pacific North West. SomeSaxifragaandChrysospleniumarecircumboreal.Others havedisjunct distributionsbetween E Asia and N America, while other taxa have separate narrow distributions in southern S America. Some species are found in wet woodlands, swamplike conditions and wet cliff edges.[2][8][1]
References
editBibliography
editBooks
edit- Byng, James W.(2014). "Saxifragales".The Flowering Plants Handbook: A practical guide to families and genera of the world.Plant Gateway Ltd. pp.156–166.ISBN978-0-9929993-1-5.
- Christenhusz, Maarten J. M.;Fay, Michael F.;Chase, Mark W.(2017). "Saxifragales".Plants of the World: An Illustrated Encyclopedia of Vascular Plants.University of Chicago Press.pp.231–244.ISBN978-0-226-52292-0.
- Kubitzki, Klaus,ed. (2007). "Introduction to Saxifragales".Flowering Plants. Eudicots: Berberidopsidales, Buxales, Crossosomatales, Fabales p.p., Geraniales, Gunnerales, Myrtales p.p., Proteales, Saxifragales, Vitales, Zygophyllales, Clusiaceae Alliance, Passifloraceae Alliance, Dilleniaceae, Huaceae, Picramniaceae, Sabiaceae.The Families and Genera of Vascular Plants. Vol. IX. Springer. pp.15–18.ISBN978-3-540-32219-1.
- Soltis, D E(2007).Saxifragaceae.pp.418–435.,inKubitzki (2007)
- Schulze-Menz, G K (1964). "Saxifragaceae". InMelchior, Hans;Werdermann, E (eds.).A. Engler's Syllabus der Pflanzenfamilien: mit besonderer Berücksichtigung der Nutzpflanzen nebst einer Übersicht über die Florenreiche und Florengebiete der Erde. (2 vols.)(12th ed.). Berlin:Gebrüder Borntraeger Verlag.pp.201–206.(see alsoSyllabus der Pflanzenfamilien)
Articles
edit- Angiosperm Phylogeny Group IV(2016)."An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV".Botanical Journal of the Linnean Society.181(1):1–20.doi:10.1111/boj.12385.
- Christenhusz, Maarten JM&Byng, J. W.(2016)."The number of known plants species in the world and its annual increase".Phytotaxa.261(3). Magnolia Press:201–217.doi:10.11646/phytotaxa.261.3.1.
- Deng, Jia-bin; Drew, Bryan T.; Mavrodiev, Evgeny V.; Gitzendanner, Matthew A.;Soltis, Pamela S.;Soltis, Douglas E.(February 2015)."Phylogeny, divergence times, and historical biogeography of the angiosperm family Saxifragaceae".Molecular Phylogenetics and Evolution.83:86–98.doi:10.1016/j.ympev.2014.11.011.PMID25479063.
- Jian, Shuguang;Soltis, Pamela S.;Gitzendanner, Matthew A.; Moore, Michael J.; Li, Ruiqi; Hendry, Tory A.; Qiu, Yin-Long; Dhingra, Amit; Bell, Charles D.;Soltis, Douglas E.(February 2008)."Resolving an ancient, rapid radiation in Saxifragales".Systematic Biology.57(1):38–57.doi:10.1080/10635150801888871.PMID18275001.
- Morgan, David R.;Soltis, Douglas E.(1993). "Phylogenetic Relationships Among Members of Saxifragaceae Sensu Lato Based on rbcL Sequence Data".Annals of the Missouri Botanical Garden.80(3): 631.doi:10.2307/2399851.JSTOR2399851.
- Soltis, Douglas E.;Soltis, Pamela S.(April 1997)."Phylogenetic relationships in Saxifragaceae sensu lato: a comparison of topologies based on 18S rDNA and rbcL sequences".American Journal of Botany.84(4):504–522.doi:10.2307/2446027.JSTOR2446027.PMID21708603.
- Soltis, Douglas E.;Morgan, David R.; Grable, Albert;Soltis, Pamela S.;Kuzoff, Robert (September 1993). "Molecular Systematics of Saxifragaceae Sensu Stricto".American Journal of Botany.80(9): 1056.doi:10.2307/2445753.JSTOR2445753.
Websites
edit- Stevens, P.F.(2019) [2001]."Saxifragales".AP Web v. 14.Missouri Botanical Garden.Retrieved25 September2019.(see alsoAngiosperm Phylogeny Website)
- POWO(2019)."Saxifragaceae Juss".Plants of the World Online.Royal Botanic Gardens, Kew.Retrieved1 December2019.
External links
edit
Media related toSaxifragaceaeat Wikimedia Commons- .Encyclopædia Britannica.Vol. 24 (11th ed.). 1911.
- Saxifragaceae in Topwalks
