| Celastrales | |
|---|---|
 | |
| Euonymus europaea, family Celastraceae | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Rosids |
| Clade: | Fabids |
| Order: | Celastrales Link[1] |
| Families | |
TheCelastrales are anorder offlowering plants found throughout thetropics andsubtropics, with only a few species extending far into thetemperate regions. The 1200[2] to 1350[3]species are in about 100genera. All but seven of these genera are in the largefamilyCelastraceae. Until recently, the composition of the order and its division into families varied greatly from one author to another.
The Celastrales are a diverse order that has no conspicuousdistinguishing characteristic, so is consequently hard to recognize.[4] Theflowers are usually small with a conspicuous nectary disk. Thestipules are small or rarely absent. Themicropyle has two openings and is therefore called a bistomal micropyle. Flowers with well-developed male and female parts are oftenfunctionally unisexual. Theseed often has anaril. Inbud, thesepals have aquincuncial arrangement. This means that two sepals are inside, two are outside, and the remaining sepal is half inside and half outside.
Perhaps the most conspicuous and unusualtrait of the Celastrales is the nectary disk, a feature that it shares with anotherrosid order,Sapindales. Since the orders are notclosely related, the disk must have been an independent development in each of theselines.
The Celastrales are a member of the Celastrales,Oxalidales (includingHuaceae), andMalpighiales (COM) clade[5] of Fabidae, with Fabidae being one of the two groups ofEurosids.[6]
Thename Celastrales was first used byThomas Baskerville in 1839.[7] In the time since Baskerville first defined the order, until the 21st century, great differences of opinion occurred about what should be included in the order and in its largest family, theCelastraceae. The family Celastraceae was the onlygroup consistently placed in the order by all authors who accepted it. Because of the ambiguity and complexity of itsdefinition, the Celastraceae became adumping ground for genera of dubiousaffinity. Several genera were assigned to this family with considerable doubt about whether they really belonged there. Also, some genera that properly belong in the Celastraceae were placed elsewhere.
By the end of the 20th century,Goupia andForsellesia had been excluded from the Celastraceae and also from the Celastrales.Goupia is now in theMalpighiales.[8]Forsellesia is now in theCrossosomatales.[9] It continues to be the subject of a dispute about whether itsproper name isForsellesia orGlossopetalon.[10]
After being placed elsewhere,Canotia,Brexia, andPlagiopteron were found to belong in the Celastraceae. The family Hippocrateaceae was found to be deeply nested within the Celastraceae and is no longer recognized as a separate family.
In 2000,Vincent Savolainenet alii found that three families -Lepidobotryaceae,Parnassiaceae, andCelastraceae - were closely related.[11] They stated that these three families should constitute the order Celastrales, and this idea was accepted by theAngiosperm Phylogeny Group, which latersubsumed the Parnassiaceae into the Celastraceae. Savolainen and co-authors also excludedLophopyxis from the Celastrales.Lophopyxis now constitutes amonogeneric family in the Malpighiales.[8]
In 2001, in amolecular phylogenetic study ofDNA sequences, Mark Simmons and others confirmed all of these results except for the placement ofLophopyxis and the Lepidobotryaceae, which they did not sample.[12]
In 2006, Li-Bing Zhang and Mark Simmons produced aphylogeny of the Celastrales based onnuclearribosomal, andchloroplastDNA.[13] Their results showed thatBhesa andPerrottetia were misplaced in the Celastraceae.Bhesa is now in theCentroplacaceae, a family in the Malpighiales.[8] andPerrottetia is in theHuerteales.[14] Zhang and Simmons foundPottingeria andMortonia to be closely related to the families Parnassiaceae and Celastraceae, as they were then defined, but not in either of them. These two genera are therefore in the Celastrales. They found thatSiphonodon andEmpleuridium are proper members of the Celastraceae, removing considerable doubt about their placement there. They also showed that the small family Stackhousiaceae, consisting of three genera, isembedded in the Celastraceae. Except fortaxa that were not sampled, these results were confirmed by the second phylogeny of the Celastrales, which was produced by Mark Simmons and several co-authors in 2008.[15]
Nicobariodendron sleumeri, the only member of its genus, continues to be an enigma. It is a small tree from theAndaman and Nicobar Islands of India. Little is known of it and it has never been sampled for DNA. It is generally thought to belong in the Celastrales,[3] but this is not a certainty. It is one of the five taxa placedincertae sedis in the angiosperms in theAPG III system ofclassification.[1]
The Celastrales have been divided into families in various ways. In theirAPG II classification in 2003, theAngiosperm Phylogeny Group recognized three families in the Celastrales –Lepidobotryaceae,Parnassiaceae, andCelastraceae. When they revised their classification in 2009, they recognized only two families becausePottingeria and the two genera of Parnassiaceae were transferred to the Celastraceae.Nicobariodendron became one of the five taxa placedincertae sedis in the angiosperms.
In the 2006 phylogeny,Nicobariodendron was not sampled, but those species that were sampled fell into two strongly supported clades. One was a small clade consisting only of the family Lepidobotryaceae. Itssister was a very large clade containing the rest of the order. The large clade consisted of five strongly supported groups. These are the family Parnassiaceae, the genusPottingeria, the genusMortonia (in the Celastraceae), and a pair of genera from the Celastraceae (Quetzalia andZinowiewia), and the rest of the Celastraceae. No relationships were resolved among these groups.
In 2008, Simmons and others produced a phylogeny of the Celastrales that achieved better resolution than the 2006 study by sampling more species and more DNA. They found the samepentatomy of five strongly supported groups that the previous study had found, but only weak to moderate support for any relationships between the five groups.[15] In the APG III system, the family Celastraceae was expanded to consist of these five groups. No one has yet published an intrafamilial classification for the expanded Celastraceae.[1]
The followingphylogenetic tree was made by combining parts of three different trees.[12][13][15] Bootstrap support is 100% except where shown. Branches with less than 50% bootstrap support are collapsed. The clade numbers are from Simmonset al. (2008).[15]
| Celastrales |
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Media related toCelastrales at Wikimedia Commons
