Buxales

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Buxales
Illustration Buxus sempervirens0.jpg
Buxus sempervirens
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Order: Buxales
Takht. ex Reveal [1]
Families

The Buxales are a small order of eudicot flowering plants, recognized by the APG IV system of 2016. The order includes the family Buxaceae; the families Didymelaceae and Haptanthaceae may also be recognized or may be included in the Buxaceae. Many members of the order are evergreen shrubs or trees, although some are herbaceous perennials. They have separate "male" (staminate) and "female" (carpellate) flowers, mostly on the same plant (i.e. they are mostly monoecious). Some species are of economic importance either for the wood they produce or as ornamental plants.

Contents

Description

The Buxales have relatively few obvious shared features distinguishing them from related groups of plants (i.e. few obvious synapomorphies). One is the presence of a particular type of alkaloid or pseudoalkaloid, pregnane steroids. They have unisexual flowers (i.e. separate staminate or "male" flowers and carpellate or "female" flowers), most being monoecious. The flowers are small, less than 7 mm across. The tepals have a single vascular bundle (trace). Other characters common to the order include leaves with entire (untoothed) margins, flowers arranged in racemes, small styles capable of receiving pollen along their entire length rather than having a separate stigma, one to two ovules per carpel, and seeds with testae (coats) made up of several cell layers. [2]

Didymeles , the sole genus in the family Didymelaceae, consists of two species of evergreen tree occurring only in Madagascar. It is dioecious, i.e. with staminate and carpellate flowers on separate plants. Buxaceae (including Haptanthaceae) is more diverse, with five or six genera totalling about 115 species, and is found in most temperate and tropical areas of the world. Most species are evergreen shrubs or small trees, but some (such as those of Pachysandra ) are herbaceous perennials. [2]

Taxonomy

In the APG III system of 2009, the order includes two families, Buxaceae and Haptanthaceae. Unlike previous classifications (including the APG II system of 2003), APG III does not recognize the family Didymelaceae, but includes the genus Didymeles in Buxaceae. [1] Subsequent research published in 2011 suggests that the Haptanthaceae are embedded in the Buxaceae, possibly as the sister to Buxus , [3] and as of September 2014 the Angiosperm Phylogeny Website no longer recognizes Haptanthaceae. [2] In the 2016 APG IV system, Haptanthaceae is incorporated into Buxaceae, which leaves Buxaceae the only family under Buxales. [4]

Phylogeny

The Buxales are placed within the eudicots but outside the core eudicots, in a paraphyletic group of basal eudicots. The monophyly of the order and its general position relative to other eudicots has been confirmed by many studies. [2] One possible phylogenetic tree is shown below, where the precise ordering of the basal eudicots is still uncertain. [2]

eudicots
basal eudicots

One difference between the basal eudicots and the core eudicots is that the latter appear to have undergone a complete duplication of the nuclear genome which is absent in the former. [5] Molecular phylogenetic studies have produced slightly different internal arrangements of the families and genera within the order; [3] hence the variation in the number of families into which it is divided.

Genera

Pachysandra terminalis Fruhbluhender Bodendecker.JPG
Pachysandra terminalis

Didymelaceae [2] or Buxaceae [1]

Buxaceae

Buxaceae [2] or Haptanthaceae [1]

Former treatment

In the Cronquist system of 1981, the Buxaceae were associated with the Euphorbiaceae s.l., [2] and the Didymelaceae were given their own order. In the APG II system of 2003, the Buxaceae were a family unplaced as to order in the eudicots, optionally including the genus Didymeles , which could alternatively be placed in its own family. [6]

Uses

Some species of the Buxaceae are of economic importance. Buxus sempervirens (common box) and Buxus macowanii (Cape box) produce hard wood valued for carving and engraving. Species are also used as ornamental garden plants and for bonsai. Common box is used for hedging and border edging. Species of Pachysandra are used as ground cover. Species of Sarcococca produce small but strongly scented flowers in the winter. [7]

Related Research Articles

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The Alismatales (alismatids) are an order of flowering plants including about 4,500 species. Plants assigned to this order are mostly tropical or aquatic. Some grow in fresh water, some in marine habitats. Perhaps the most important food crop in the order is the corm of the taro plant, Colocasia esculenta.

<span class="mw-page-title-main">Proteales</span> Order of eudicot flowering plants

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<span class="mw-page-title-main">Austrobaileyales</span> Order of flowering plants

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<span class="mw-page-title-main">Gunnerales</span> Order of flowering plants

The Gunnerales are an order of flowering plants. In the APG III (2009) and APG IV systems (2016), the order contains two genera: Gunnera and Myrothamnus (Myrothamnaceae). In the Cronquist system (1981), the Gunneraceae were in the Haloragales and Myrothamnaceae in the Hamamelidales. DNA analysis proved definitive, but the grouping of the two families was a surprise, given their very dissimilar morphologies. In the older systems of Cronquist and Takhtajan (1997), the Gunneraceae were in the Rosidae, and the Myrothamnaceae were in the Hamamelids. In modern classification systems, such as APG III and APG IV, this order was the first to derive from the core eudicots.

<i>Amborella</i> Species of shrub

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<span class="mw-page-title-main">Angiosperm Phylogeny Group</span> Collaborative research group for the classification of flowering plants

The Angiosperm Phylogeny Group (APG) is an informal international group of systematic botanists who collaborate to establish a consensus on the taxonomy of flowering plants (angiosperms) that reflects new knowledge about plant relationships discovered through phylogenetic studies.

<span class="mw-page-title-main">Buxaceae</span> Family of flowering plants

The Buxaceae are a small family of six genera and about 123 known species of flowering plants. They are shrubs and small trees, with a cosmopolitan distribution. A seventh genus, sometimes accepted in the past (Notobuxus), has been shown by genetic studies to be included within Buxus.

<span class="mw-page-title-main">Dilleniaceae</span> Family of flowering plants

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<i>Euptelea</i> Genus of flowering plants

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<i>Didymeles</i> Genus of trees

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<span class="mw-page-title-main">Berberidopsidaceae</span> Family of flowering plants

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<i>Halophytum</i> Genus of flowering plants

Halophytum ameghinoi is a species of herbaceous plant endemic to Patagonia. It is the only species in the genus Halophytum. It is a succulent annual plant, with simple, fleshy, alternate leaves. The plants are monoecious, with solitary female flowers and inflorescences of male flowers on the same plant .

<i>Trochodendron aralioides</i> Species of tree

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<i>Haptanthus</i> Genus of shrub

Haptanthus is a monotypic genus containing the sole species Haptanthus hazlettii, a shrub or small tree known only from the locality of Matarras in the Arizona Municipality in Honduras. Its flowers are unique among the flowering plants. A single "female" (carpellate) flower has two branches on either side which carry "male" (staminate) flowers. The flowers are very simple, lacking obvious sepals or petals. The family placement of the genus has been uncertain, but based on molecular phylogenetic research, it is included in the family Buxaceae as of September 2014. Very few individuals have ever been found and its habitat is threatened by logging.

Aphloia is a genus of flowering plants that contains a single species, Aphloia theiformis, the sole species of the monogeneric family Aphloiaceae. It is a species of evergreen shrubs or small trees occurring in East Africa, Madagascar, the Mascarene Islands and the Seychelles.

<i>Geissoloma</i> Monotypic genus of flowering plants native to the Cape Province of South Africa

Geissoloma is a genus of flowering plants in the monotypic family Geissolomataceae, native to the Cape Province of South Africa. Geissoloma marginatum is the only species in the family. It is sometimes called guyalone in English. The plants are xerophytic evergreen shrubs and are known to accumulate aluminum.

References

  1. 1 2 3 4 Angiosperm Phylogeny Group (2009), "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III", Botanical Journal of the Linnean Society, 161 (2): 105–121, doi: 10.1111/j.1095-8339.2009.00996.x
  2. 1 2 3 4 5 6 7 8 Stevens, P.F., "Buxales", Angiosperm Phylogeny Website, retrieved 2014-09-25
  3. 1 2 Shipunov, A.B.; Shipunova, E. (2011), "Haptanthus story: Rediscovery of enigmatic flowering plant from Honduras", American Journal of Botany, 98 (4): 761–763, doi:10.3732/ajb.1000307, PMID   21613172
  4. Angiosperm Phylogeny Group (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 .
  5. Stevens, P.F. (2001–2012), "Core eudicots / Gunneridae", Angiosperm Phylogeny Website, retrieved 2014-09-26
  6. Angiosperm Phylogeny Group II (2003), "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG II", Botanical Journal of the Linnean Society, 141 (4): 399–436, doi:10.1046/j.1095-8339.2003.t01-1-00158.x
  7. Chant, S.R. (1978), "Buxaceae", in Heywood, V.H.; Moore, D.M.; Richardson, I.B.K. & Stearn, W.T. (eds.), Flowering Plants of the World , Oxford, etc.: Oxford University Press, pp.  183–5, ISBN   9780195210378