Saxifragales

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Saxifragales
Temporal range: 89.5–0 
Ma
 Turonian - Recent
Saxifraga granulata L.
meadow saxifrage
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade:
Core eudicots
Clade: Superrosids
Order: Saxifragales
J.Presl[1]
Type genus
Saxifraga
Families[1]
Synonyms
  • Cercidiphyllales
  • Crassulales
  • Daphniphyllales
  • Grossulariales
  • Haloragales
  • Hamamelidales
  • Iteales
  • Paeoniales
  • Sedales
Floral diagram of Saxifraga flower
Floral diagram Saxifraga: Bicarpellate Gynoecium

Saxifragales (

genera, with nearly 2,500 species. Of the 15 families, many are small, with eight of them being monotypic (having only a single genus). The largest family is the Crassulaceae (stonecrops), a diverse group of mostly succulent plants, with about 35 genera. Saxifragales are found worldwide, primarily in temperate to subtropical zones, rarely being encountered growing wild in the tropics; however, many species are now cultivated throughout the world as knowledge of plant husbandry has improved. They can be found in a wide variety of environments, from deserts to fully aquatic habitats, with species adapted to alpine, forested or fully-aquatic habitats. Many are epiphytic or lithophytic
, growing on exposed cliff faces, on trees or on rocks, and not requiring a highly organic or nutrient-dense substrate to thrive.

Globally, the saxifrages have a wide variety of uses by humans, ranging from

Grossulariaceae (currants and gooseberries), particularly blackcurrants, redcurrants and white currants
.

Overall, the order is extremely

perennial herbs and succulent plants, as well as aquatic and semi-aquatic
species. The order's high degree of diversity, in terms of vegetative and reproductive traits (and sheer amount of species), can make it challenging to find any common or unifying features amongst the respective genera.

In the

molecular studies
may suggest an older origin, from the early Cretaceous (102–108 Myr), with rapid and early diversification to more modern forms.

Description

The

carpel number, as well as ovary position (see Biogeography and evolution).[3][4]

anthers

This degree of diversity makes defining

herbaceous families of Crassulaceae and Saxifragaceae exhibit woody features as a secondary transition.[5][6][7]

Taxonomy

Saxifragales is a relatively small

genera and about 2,470 species.[3]

History

First page of Lindley's Saxifragales from 1853
John Lindley's description of Saxifragales 1853

Saxifragales was first described in 1820 by

Dicotyledons, also called Magnoliopsida.[11]

Phylogeny

The

monophyletic group.[13]

In the initial APG publication (1998), the Saxifragales were identified within the

angiosperms.[3][1][20] Among the rosids, they share a number of similarities with the Rosales, particularly Rosaceae, including a hypanthium, five part flowers and free floral parts.[21] As circumscribed, Saxifragales account for 1.3% of eudicot diversity.[22]

Cladogram of Saxifragales relationships among core eudicots[1][12][23]
Core eudicots

Gunnerales

126
Pentapetalae

superasterids

Dilleniales

125
superrosids

rosids

116

Saxifragales

108
124
128
130
Numbers indicate
divergence times
in Myr

Biogeography and evolution

stem groups respectively. Within the order Saxifragales, the molecular data imply a very rapid initial diversification time of about 6–8 Myr, between 112 and 120 Myr, with major lineages appearing within 3–6 Myr.[30][3][31]

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

Macaronesian taxa (Aeonieae) have 8–12, with up to 32 carpels for Aeonium.[3]

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.[3] The ancestral habitat appears to be forests, followed by early diversification into desert and aquatic habitats, with shrubland the most recent colonization.[2]

Species diversification was rapid following a transition from a warmer, wetter Earth in the Eocene (56–40 Myr) to early Miocene (23–16 Myr), to the cooler drier conditions of the mid-Miocene (16–12 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.[32]

Subdivision

The first APG classification (1998) placed 13 families within the order Saxifragales:[33]

This was subsequently revised to 15, in the fourth version (2016).

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.[3]

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

Pterostemon that constitute Pterostemonaceae within Iteaceae, and all subsequent versions have maintained this practice.[16] 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.[35][1]

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

DNA sequence for the rbcL gene from Whittonia. This sequence turned out to be not from Whittonia, but from other plants whose DNA had contaminated the sample.[36] After placement in Saxifragales, it was expanded to include Soyauxia in 2007,[37] and Medusandra in 2009.[38]

In the first of the subclades of the remaining Saxifragales, Paeoniaceae possesses many

Glaucidium,[40][41] prior to transfer to Saxifragales as sister to the woody clade.[30][42]

In the woody clade, the genus

Trochodendrales.[44] Daphniphyllum was always thought to have an anomalous combination of characters[45][45] and was placed in several different orders before molecular phylogenetic analysis showed it to belong to Saxifragales.[46]

In the core Saxifragales, Crassulaceae[47] and Tetracarpaeaceae[48] have been associated with Saxifragaceae, while Penthorum has been associated both with Crassulaceae and Saxifragaceae,[49] 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,[50] and it was subsequently transferred.[51] Haloragaceae was included in Myrtales,[52] before being placed in Saxifragales.[53]

The other "core" group, the Saxifragaceae alliance comprises four families: Pterostemonaceae, Iteaceae, Grossulariaceae, and Saxifragaceae,

Pterostemon in Iteaceae.[54]

Most of the families are

Grossulariaceae (150–200), Haloragaceae (150), and Hamamelidaceae (100).[22][30][58]

The relationships of the Saxifragales families to each other is shown in the following

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.[31]
The number of genera in each family is shown in parentheses:

Cladogram of Saxifragales families[1][22][30]
Saxifragales

Peridiscaceae (4)

 97 

Paeonia (Paeoniaceae)

 woody clade 

Liquidambar (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)

Saxifragaceae (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

Families

Botanical illustration of Peridiscus lucidus
Peridiscus lucidus

Peridiscaceae

Main article: Peridiscaceae

The Peridiscaceae (Ringflower family) are a small tropical family of 4 genera and 11–12 species of small trees and shrubs found in the

Greek, peri (around) discos (ring).[6][61][21]

Paeonia officinalis growing in Hungary
Paeonia officinalis

Paeoniaceae

Main article:
Paeoniaceae

The Paeoniaceae (Peony family) consist of a single genus (Paeonia) with about 33 species of perennial herbs and small shrubs with showy flowers, found from the Mediterranean to Japan, but two species occur in western N America. They are commercially important as popular garden ornamentals, cultivated since antiquity, and have been used medicinally. The herbaceous varieties are derived from

P. suffruticosa (tree peony), both Asian species. The botanical name comes from its Greek name, paionia, named in turn for the God Pan.[6][61][21]

Liquidambar styraciflua tree
Liquidambar styraciflua

Altingiaceae

Main article: Altingiaceae

The Altingiaceae (Sweetgum family) consist of a single genus (

Willem Alting, and Liquidambar for liquid ambar, Arabic for the resin.[6][61][21]

Branch of Hamamelis virginiana showing flowers and leaves
Hamamelis virginiana

Hamamelidaceae

Main article: Hamamelidaceae

The Hamamelidaceae (Witch-hazel family) consists of trees and shrubs with a widespread distribution, but main centres in East Asia and Malaysia. They are found in wet woodlands and forested slopes. The family has 26 genera and about 80–100 species, in five subfamilies, of which the nominative, Hamamelidoideae, contains over 75% of the genera. The species have uses as medicaments, timber and ornamental plants for their flowers, such as

Hamamelis (witch hazel) or leaves, such as Parrotia persica (Persian ironwood). The family and nominative genus is named for the Greek hamamelis, the wych elm.[61][21][6]

Cercidiphyllum japonicum
Cercidiphyllum japonicum

Cercidiphyllaceae

Main article:
Cercidiphyllaceae

The Cercidiphyllaceae (Caramel-tree family) are a small family of deciduous trees found in China and Japan, with a single genus, Cercidiphyllum and two species,

poplar) and fyllon (leaf), from a supposed similarity in leaves.[61][21]

Daphniphyllum macropodum
Daphniphyllum macropodum

Daphniphyllaceae

Main article:
Daphniphyllaceae

The Daphniphyllaceae (Laurel-leaf family) consist of a single genus, Daphniphyllum, with about 30 species. They are evergreen unisexual trees and shrubs distributed in SE Asia and the Solomon Islands. The dried leaves of Daphniphyllum macropodum[a] have been used for smoking in Japan and Siberia. The name is derived from the Greek words dafne (laurel) and fyllon (leaf), from a supposed resemblance to the leaves of the former (Laurus nobilis).[61][21]

Crassula perfoliata
Crassula perfoliata

Crassulaceae

Main article: Crassulaceae

The Crassulaceae (Orpine and Stonecrop family) are a medium size diverse and cosmopolitan family, that form the largest family within Saxifragales. They are mainly

Crassulacean Acid Metabolism). Genera vary from 7 to 35, depending on the circumscription of the large genus Sedum, and there are about 1,400 species. Uses are diverse, including spices, medicaments and roof coverings as well as ornamental rock garden and household plants such as the S African Crassula ovata, the jade or money plant. The name is derived from the Latin, crassus (thick), referring to the fleshy leaves.[61][21][6]

Aphanopetalum resinosum vine
Aphanopetalum resinosum

Aphanopetalaceae

Main article:
Aphanopetalaceae

The Aphanopetalaceae (Gum-vine family) consists of a single genus of Australian climbing shrubs, Aphanopetalum, which has two species, A. clematidium (SW Australia) and A. resinosum (Queensland, NSW). The name is derived from the Greek words afanos (inconspicuous) and petalon (petal).[61][21]

Tetracarpaea tasmannica

Tetracarpaeaceae

Main article:
Tetracarpaeaceae

The Tetracarpaeaceae (Delicate-laurel family) is a very small evergreen Australian shrub family with a single genus, Tetracarpaea and a single species, T. tasmannica, confined to subalpine Tasmania. The name is derived from the Greek words tetra (four) and carpos (fruit), referring to the ovaries which have four carpels.[61][21][6]

Flowers of Penthorum sedoides
Penthorum sedoides

Penthoraceae

Main article:
Penthoraceae

The Penthoraceae (Ditch-stonecrop family) is a very small family of rhizomatous perennial herbs found in eastern N America and E Asia, in mainly wet environments. It consists of a single genus, Penthorum with two species, P. sedoides in N America and P. chinense from Siberia to Thailand. P. sedoides is used in aquaria and water gardens.[62] The name is derived from the Greek word pente (five) referring to the five-part fruit.[61][21][6]

Flowers and leaves of Haloragis erecta
Haloragis erecta

Haloragaceae

Main article: Haloragaceae

The Haloragaceae (Water-milfoil family) is a small family of trees, shrubs, perennial, annual terrestrial, marsh and aquatic herbs with global distribution, but especially Australia. It consists of 9–11 genera and about 145 species. The largest genus is

Haloragodendron, is a shrub and is confined to S Australia. The family and nominative genus, Haloragis are named from the Greek words halas (salt) and rhoges (berries).[61][21][6]

Itea virginica plant
Itea virginica

Iteaceae

Main article: Iteaceae

The Iteaceae (Sweetspire family) is a widespread small family of trees and shrubs, with 2 genera, and 18–21 species, found in tropical to northern temperate regions. The larger genus,

Pterostemon (c. 2 spp) is confined to Oaxaca, Mexico. I. virginica and I. ilicifolia, from China, are valued as ornamental shrubs. The name is derived from the Greek word itea (willow) for its rapid growth and similar leaf form.[61][21][6]

Ribes rubrum

Grossulariaceae

Main article:
Grossulariaceae

The Grossulariaceae (Gooseberry family) are shrubs that are usually deciduous. The single genus,

R. nigrum (blackcurrant). They are found in temperate northern hemisphere regions but extending through the Andes into S America. The family name is derived from the Latin word grossulus (an unripe fig), and Ribes is Latinised from the semitic word ribas (acid taste).[61][21][6]

Flowers of Saxifraga granulata
Saxifraga granulata

Saxifragaceae

Main article: Saxifragaceae

The Saxifragaceae (Saxifrage family) are mainly perennial herbs distributed throughout the Northern Hemisphere and Andes, and New Guinea, in damp woodlands and cooler northern regions, rarely aquatic, but are adapted to a wide range of moisture conditions. The family, greatly reduced, includes 35 genera and about 640 species, in two lineages, saxifragoids (e.g.

kidney stones.[61][21][6]

Cynomorium coccineum

Cynomoriaceae

Main article:
Cynomoriaceae

The Cynomoriaceae (Tarthuth or Maltese Mushroom family) consists of a single genus, Cynomorium with one or two species,

C. songaricum (central Asia and China; sometimes treated as a variety of C. coccineum). They are perennial bisexual herbaceous parasitic plants lacking chlorophyll, from deserts and arid regions. They have been harvested for food, as a dye and in traditional medicine. The name is derived from two Greek words kynos (dog), and morion (penis), for its shape.[61][21]

Distribution and habitat

Saxifragales are found worldwide,[6] though primarily in temperate zones and rarely in the tropics.[61] They occupy a wide variety of habitats from arid desert (Crassulaceae) to aquatic conditions (Haloragaceae), with 6 families, including North American species, that are obligate aquatic (fully dependent on an aquatic environment),[63] and including forests, grasslands and tundra. Saxifragales exceeds all other comparably sized clades in terms of diversity of habitats.[2] Most of the diversity occurs in temperate (including montane and arid) conditions that expanded globally during cooling and drying trends in the last 15 My.[32]

The most common habitats are forests and cliffs, with about 300 species occupying each, but with forests being the most diverse phenotypically, where nearly all families are represented. In contrast desert and tundra, with only two families each, contain only about 10% of species. About 90% of species can be assigned to a single habitat.[2]

Conservation

Whittonia (Peridiscaceae) is thought to be extinct. As of 2019 the

near threatened species. Among the most threatened Saxifragales are Aichryson dumosum and Monanthes wildpretii (Crassulaceae), Haloragis stokesii and Myriophyllum axilliflorum (Haloragaceae), Ribes malvifolium and R. sardoum (Grossulariaceae), Saxifraga artvinensis (Saxifragaceae) and Molinadendron hondurense (Hamamelidaceae).[64]

Cultivation

A number of Saxifragales genera are commercially cultivated.

green roofs".[68][47] In particular, cultivars of the Madagascan Kalanchoe blossfeldiana, e.g. 'Florists kalanchoe' have achieved commercial success throughout the world, being popular Christmas decorative plants.[69][70] The Haloragaceae aquatic genus Myriophyllum and the closely related Proserpinaca are cultivated for the commercial aquarium trade.[71] Myriophyllum is also economically important for purification of water and as feed for pigs, ducks, and fish, and polishing wood.[72]

Fields of black currants growing in U.K.
Blackcurrant crops, UK

A number of Ribes (Grossulariaceae) are in commercial production, concentrated in Europe and the USSR from species native to those areas.

R. rubrum (red currant).[74][75] World Ribes crop production was over 750,000 tons in 2002, of which about 150,000 tons were gooseberries, and the largest group blackcurrants.[76]

Uses

Plants in the order Saxifragales have found a wide variety of uses, including traditional medicines, ornamental, household, aquarium, pond and garden plants, spices, foodstuffs (fruit and greens), dyestuffs, smoking, resin, timber, and roof coverings.[61]

See also

Notes

  1. ^ D. humile is a synonym of the accepted D. macropodum

References

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  3. ^ a b c d e f g h Soltis et al 2013.
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  5. ^ Soltis et al 2006.
  6. ^ a b c d e f g h i j k l m Berry 2017.
  7. ^ Carlsward et al 2011.
  8. ^ Berchtold & Presl 1820, pp. 259–60.
  9. ^ Dumortier 1829, p. 38.
  10. ^ Lindley 1853, pp. 566–575.
  11. ^ Singh 2004.
  12. ^ a b Cole et al 2019.
  13. ^ Kubitzki 2007a.
  14. ^ Moore et al 2010.
  15. ^ Zeng et al 2017.
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  17. ^ Burleigh et al 2009.
  18. ^ Wang et al 2009.
  19. ^ APG III 2009.
  20. ^ Soltis et al 2018.
  21. ^ a b c d e f g h i j k l m n o p Byng 2014.
  22. ^ a b c Stevens 2019.
  23. ^ Tank et al 2015.
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  27. ^ Hernández-Castillo & Cevallos-Ferriz 1999.
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  29. ^ Endress 1989.
  30. ^ a b c d e f Jian et al 2008.
  31. ^ a b Li et al 2019.
  32. ^ a b Folk et al 2019.
  33. ^ APG I 1998.
  34. ^ Engler 1930.
  35. ^ Bellot et al 2016.
  36. ^ Davis & Chase 2004.
  37. ^ Soltis et al 2007.
  38. ^ Wurdack & Davis 2009.
  39. ^ Tamura 2007.
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  46. ^ Kubitzki 2007b.
  47. ^ a b Thiede & Eggli 2007.
  48. ^ Hils et al 1988.
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  50. ^ Dickison et al 1994.
  51. ^ Bradford, Fortune-Hopkins & Barnes 2004.
  52. ^ Kubitzki 2007c.
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  55. ^ Kubitzki 2007d.
  56. ^ Ickert-Bond & Wen 2006.
  57. ^ Ickert-Bond & Wen 2013.
  58. ^ Kubitzki 2007a, pp. 15–18.
  59. ^ Dong et al 2018.
  60. ^ Ding et al 2019.
  61. ^ a b c d e f g h i j k l m n o p q r Christenhusz et al 2017.
  62. ^ a b Les 2017.
  63. ^ Les 2017, p. 745.
  64. ^ IUCN 2019.
  65. ^ Auer & Greenberg 2009.
  66. ^ Kormanik 1990.
  67. ^ Gapinski 2014.
  68. ^ Earle & Lundin 2012.
  69. ^ Smith et al 2019.
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  74. ^ Doronina & Terekhina 2009.
  75. ^ Gros d'Aillon 2016.
  76. ^ Brennan 2008a.

Bibliography

Books

Chapters
Historical

Articles

Angiosperms
Eudicots
Saxifragales

APG

Saxifragales families

Paleontology

Websites
Images

External links

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