Saxifragaceae

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Saxifragaceae
Foamflower.jpg
Tiarella
(Foamflower)
Scientific classification Red Pencil Icon.png
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Order: Saxifragales
Family: Saxifragaceae
Juss.
Type genus
Saxifraga
L.
Clades

See text

Saxifragaceae Distribution.svg
The range of Saxifragaceae
Saxifraga granulata Saxifraga granulata 140505.jpg
Saxifraga granulata
Astilbe rivularis Astilbe rivularis - Flickr - peganum (1).jpg
Astilbe rivularis

Saxifragaceae is a family of herbaceous perennial flowering plants, within the core eudicot order Saxifragales. The taxonomy of the family has been greatly revised and the scope much reduced in the era of molecular phylogenetic analysis. The family is divided into ten clades, with about 640 known species in about 35 accepted genera. About half of these consist of a single species, but about 400 of the species are in the type genus Saxifraga . The family is predominantly distributed in the northern hemisphere, but also in the Andes in South America.

Contents

Description

Species are herbaceous perennials (rarely annual or biennial), sometimes succulent or xerophytic, often with perennating rhizomes. The leaves are usually basally aggregated in alternate rosettes, sometimes on inflorescence stems. 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. The flowers are hermaphroditic (bisexual), rarely unisexual (androdioecious), actinomorphic (rarely zygomorphic). The perianth is placed on a hypanthium that may be free or may be partly fused with the ovary (which is then semi-inferior). There are usually five sepals, but there may be three to ten, fused with the hypanthium, occasionally petaloid. The petals are clawed, sometimes cleft at the tip or finely dissected. Flowers have five to ten stamens, 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) carpels usually fused at the base, sometimes free, each topped with stylodium and capitate stigma. The ovules are few to many, with axile or parietal placentation and two to three styles. The fruit is usually a septicidal capsule or follicle, with numerous small seeds. [1] [2]

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 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 Cronquist (1981), Dahlgren (1983), Engler (1890), Hutchinson (1973), Schulze-Menz (1964), [3] Takhtajan (1980) and Thorne (1992) (for a history, see Morgan & Soltis (1993) . In its broadest circumscription, it included 17 subfamilies. [3] 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. [4] [5]

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). [4] [6]

The reduced Saxifragaceae is distinguished by being referred to as Saxifragaceae sensu stricto (s.s.), corresponding to the Saxifragoideae a natural monophyletic group. [7] Historically, the Saxifragaceae has been placed in either the orders 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. [8] [4] [6]

Cladogram I: Saxifragales families [9] [10] [6]
Saxifragales

Peridiscaceae (4)

 97 

Paeonia (Paeoniaceae)

 woody clade 

Liquidamber (Altingiaceae)

 69 
 98 

Hamamelidaceae (27)

 95 

Cercidiphyllum (Cercidiphyllaceae)

Daphniphyllum (Daphniphyllaceae)

 core Saxifragales 

Crassulaceae (34)

 Haloragaceae s.l.

Aphanopetalum (Aphanopetalaceae)

Tetracarpaea (Tetracarpaeaceae)

Penthorum (Penthoraceae)

Haloragaceae s.s. (8)

 Saxifragaceae alliance 

Iteaceae (including Pterostemonaceae) (2)

Ribes (Grossulariaceae)

Saxifragaceaes.s. (33)

100% maximum likelihood bootstrap support except 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

Heuchera americana American Alumroot Heuchera americana 'Garnet' Stalk 2448px.JPG
Heuchera americana
Rodgersia podophylla Rodgersia podophylla 4587.jpg
Rodgersia podophylla
Micranthes merkii Saxifraga merkii var idsuroei s2.jpg
Micranthes merkii

Numerous attempts have been made to subdivide Saxifragoideae (Saxifragaceae s.s.). These have included dividng 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 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: [7] [8] [1]

Clades (Genera (Species))

The clades and subclades are related as shown in the cladogram: [8]

Cladogram II: Infrafamilial structure of Saxifragaceae
Saxifragaceae
Saxifragoids

Saxifraga

30
Heucheroids

Leptarrhena

8

Saniculiphyllum

Boykinia

11
16
18

Astilbe

14
20

Heuchera

7

Cascadia

19

Darmera

10

Peltoboykinia

23

Micranthes

15
27
29
31
38
Diversification time in Mya underneath group names

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. [7] [11] [2] [8]

Evolution and biogeography

The crown group of Saxifragaceae diversified at about 38  Mya (Mid–Late Eocene), with the two main lineages diversifying arising at about 30 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. [8]

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. [2]

Distribution and habitat

Primarily Northern hemisphere temperate and arctic regions, and also tropical montane, including the Americas, Europe, North Africa (including montane Ethiopia) and temperate and subtropical Asia to Luzon and New Guinea. In the Americas it extends south to central Mexico and the Andes to Tierra del Fuego. Centres of diversity are western N America, East Asia and the Himalayas. The largest concentration of genera are in the Pacific North West. Some Saxifraga and Chrysosplenium are circumboreal. Others have disjunct distributions between 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]

Related Research Articles

Malpighiales Eudicot order of flowering plants

The Malpighiales comprise one of the largest orders of flowering plants, containing about 36 families and more than 16,000 species, about 7.8% of the eudicots. The order is very diverse, containing plants as different as the willow, violet, poinsettia, manchineel, rafflesia and coca plant, and are hard to recognize except with molecular phylogenetic evidence. It is not part of any of the classification systems based only on plant morphology. Molecular clock calculations estimate the origin of stem group Malpighiales at around 100 million years ago (Mya) and the origin of crown group Malpighiales at about 90 Mya.

Rosales Order of flowering plants

Rosales is an order of flowering plants. It is sister to a clade consisting of Fagales and Cucurbitales. It contains about 7,700 species, distributed into about 260 genera. Rosales comprise nine families, the type family being the rose family, Rosaceae. The largest of these families are Rosaceae (90/2500) and Urticaceae (54/2600). The order Rosales is divided into three clades that have never been assigned a taxonomic rank. The basal clade consists of the family Rosaceae; another clade consists of four families, including Rhamnaceae; and the third clade consists of the four urticalean families.

Saxifragales Order of Eudicot flowering plants in the Superrosid clade

The Saxifragales (saxifrages) are an order of flowering plants (Angiosperms). They are an extremely diverse group of plants which include trees, shrubs, perennial herbs, succulent and aquatic plants. The degree of diversity in terms of vegetative and floral features makes it difficult to define common features that unify the order.

Cornales

The Cornales are an order of flowering plants, early diverging among the asterids, containing about 600 species. Plants within the Cornales usually have four-parted flowers, drupaceous fruits, and inferior to half-inferior gynoecia topped with disc-shaped nectaries.

Geraniales Order of flowering plants in the rosid subclade of eudicots

Geraniales are a small order of flowering plants, included within the rosid subclade of eudicots. The largest family in the order is Geraniaceae with over 800 species. In addition, the order includes the smaller Francoaceae with about 40 species. Most Geraniales are herbaceous, but there are also shrubs and small trees.

Crassulaceae A family of flowering plants comprising members popular for horticulture and characterized by a peculiar photosynthetic metabolism adapted to arid conditions

The Crassulaceae, also known as the stonecrop family or the orpine family, are a diverse family of dicotyledon flowering plants characterized by succulent leaves and a unique form of photosynthesis, known as Crassulacean acid metabolism (CAM). Flowers generally have five floral parts. Crassulaceae are usually herbaceous but there are some subshrubs, and relatively few treelike or aquatic plants. Crassulaceae are a medium size monophyletic family in the core eudicots, among the order Saxifragales, whose diversity has made infrafamilial classification very difficult. The family includes approximately 1,400 species and 34–35 genera, depending on the circumscription of the genus Sedum, and distributed over three subfamilies. Members of the Crassulaceae are found worldwide, but mostly in the Northern Hemisphere and southern Africa, typically in dry and/or cold areas where water may be scarce, although a few are aquatic.

<i>Ribes</i> Genus of flowering plants in the order Saxifragales

Ribes is a genus of about 200 known species of flowering plants native throughout the temperate regions of the Northern Hemisphere. The various species are known as currants or gooseberries, and some are cultivated for their edible fruit or as ornamental plants. Ribes is the only genus in the family Grossulariaceae.

Ulmaceae Family of flowering plants

The Ulmaceae are a family of flowering plant that includes the elms, and the zelkovas. Members of the family are widely distributed throughout the north temperate zone, and have a scattered distribution elsewhere except for Australasia.

Hamamelidaceae Witch-hazel family, of shrubs and small trees, in the order Saxifragales

Hamamelidaceae, commonly referred to as the witch-hazel family, is a family of flowering plants in the order Saxifragales. The clade consists of shrubs and small trees positioned within the woody clade of the core Saxifragales. An earlier system, the Cronquist system, recognized Hamamelidaceae in the Hamamelidales order.

Asphodelaceae Family of flowering plants in the order Asparagales

Asphodelaceae is a family of flowering plants in the order Asparagales. Such a family has been recognized by most taxonomists, but the circumscription has varied widely. In its current circumscription in the APG IV system, it includes about 40 genera and 900 known species. The type genus is Asphodelus.

Polypodiales

The order Polypodiales encompasses the major lineages of polypod ferns, which comprise more than 80% of today's fern species. They are found in many parts of the world including tropical, semitropical and temperate areas.

Cyatheaceae

The Cyatheaceae are a family of tree ferns, the scaly tree ferns, one of eight families in the order Cyatheales in the Pteridophyte Phylogeny Group classification of 2016. Alternatively, the family may defined much more broadly as the only family in the Cyatheales, with the PPG I family treated as the subfamily Cyatheoideae. The narrower circumscription is used in this article.

Rosids Large clade of flowering plants

The rosids are members of a large clade of flowering plants, containing about 70,000 species, more than a quarter of all angiosperms.

Asparagaceae Family of plants

Asparagaceae is a family of flowering plants, placed in the order Asparagales of the monocots. Its best known member is Asparagus officinalis, garden asparagus.

Peridiscaceae Family of flowering plants in the order Saxifragales

Peridiscaceae is a family of flowering plants in the order Saxifragales. Four genera comprise this family: Medusandra, Soyauxia, Peridiscus, and Whittonia., with a total of 12 known species. It has a disjunct distribution, with Peridiscus occurring in Venezuela and northern Brazil, Whittonia in Guyana, Medusandra in Cameroon, and Soyauxia in tropical West Africa. Whittonia is possibly extinct, being known from only one specimen collected below Kaieteur Falls in Guyana. In 2006, archeologists attempted to rediscover it, however, it proved unsuccessful.

Haloragaceae Family of flowering plants in the Eudicot order Saxifragales

Haloragaceae is a eudicot flowering plant family in the order Saxifragales, based on the phylogenetic APG system. In the Cronquist system, it was included in the order Haloragales.

Lepuropetalon is a genus of flowering plants in the family Celastraceae. Before it was placed in the family when it was defined by the Angiosperm Phylogeny Group's APG III system in 2009, it had been placed with Parnassia in the family Parnassiaceae, now usually treated as a segregate of Celastraceae. When their most recent revision of Angiosperm classification was published in 2016, it retained its position in the family Celastraceae. Lepuropetalon has only one species, Lepuropetalon spathulatum. It is a winter annual that is most abundant in eastern Texas and western Louisiana. From there, it occurs sporadically southward into Mexico, and eastward through the Atlantic and Gulf coastal plain, and rarely in the Piedmont Plateau, to North Carolina. It has a disjunct distribution. In addition to the area mentioned above, it is also found in Uruguay and central Chile.

<i>Tetracarpaea</i>

Tetracarpaea is the only genus in the flowering plant family Tetracarpaeaceae. Some taxonomists place it in the family Haloragaceae sensu lato, expanding that family from its traditional circumscription to include Penthorum and Tetracarpaea, and sometimes Aphanopetalum as well.

Sempervivoideae Largest of 3 subfamilies in the flowering plant family Crassulaceae

Sempervivoideae is the largest of three subfamilies in the Saxifragales family Crassulaceae, with about 20–30 genera with succulent leaves. Unlike the two smaller subfamilies, it is distributed in temperate climates. The largest genus in this subfamily is Sedum, with about 470 species.

References

  1. 1 2 3 4 5 Byng 2014.
  2. 1 2 3 4 5 Christenhusz et al 2017.
  3. 1 2 Schulze-Menz 1964.
  4. 1 2 3 Morgan & Soltis 1993.
  5. Soltis & Soltis 1997.
  6. 1 2 3 APG IV 2016.
  7. 1 2 3 4 Soltis et al 1993.
  8. 1 2 3 4 5 6 Deng et al 2015.
  9. Jian et al 2008.
  10. Stevens 2019.
  11. Christenhusz & Byng 2016.

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