Buxales | |
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Buxus sempervirens | |
Scientific classification ![]() | |
Kingdom: | Plantae |
Clade: | Tracheophytes |
Clade: | Angiosperms |
Clade: | Eudicots |
Order: | Buxales Takht. ex Reveal [1] |
Families | |
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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.
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]
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 [update] 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]
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]
| 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.
Didymelaceae [2] or Buxaceae [1]
Buxaceae
Buxaceae [2] or Haptanthaceae [1]
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]
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]
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.
Proteales is an order of flowering plants consisting of three families. The Proteales have been recognized by almost all taxonomists.
Austrobaileyales is an order of flowering plants consisting of about 100 species of woody plants growing as trees, shrubs and lianas. The best-known species is Illicium verum, commonly known as star anise. The order belongs to the group of basal angiosperms, the ANA grade, which diverged earlier from the remaining flowering plants. Austrobaileyales is sister to all remaining extant angiosperms outside the ANA grade.
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.
Amborella is a monotypic genus of understory shrubs or small trees endemic to the main island, Grande Terre, of New Caledonia in the southwest Pacific Ocean. The genus is the only member of the family Amborellaceae and the order Amborellales and contains a single species, Amborella trichopoda. Amborella is of great interest to plant systematists because molecular phylogenetic analyses consistently place it as the sister group to all other flowering plants, meaning it was the earliest group to evolve separately from all other 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.
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.
Dilleniaceae is a family of flowering plants with 11 genera and about 430 known species. Such a family has been universally recognized by taxonomists. It is known to gardeners for the genus Hibbertia, which contains many commercially valuable garden species.
Euptelea is a genus of two species of flowering plants in the monogeneric family Eupteleaceae. The genus is found from Assam east through China to Japan, and consists of shrubs or small trees:
Didymeles is a genus of flowering plants. It is variously treated as the only genus of the family Didymelaceae — or in the family Buxaceae, as in the APG IV system.
Berberidopsidaceae is a family of flowering plants. Such a family has only recently been recognized by more than a few taxonomists: the plants involved have often been treated as belonging to family Flacourtiaceae.
The APG II system of plant classification is the second, now obsolete, version of a modern, mostly molecular-based, system of plant taxonomy that was published in April 2003 by the Angiosperm Phylogeny Group. It was a revision of the first APG system, published in 1998, and was superseded in 2009 by a further revision, the APG III system.
Asteropeia is a genus of flowering plants. The genus contains 8 known species of shrubs and small trees, all endemic to Madagascar. It is the sole genus in family Asteropeiaceae. Members of the family are evergreen trees or shrubs.
Physena is the sole genus of the flowering plant family Physenaceae. It contains two species of shrubs and small trees which are endemic to Madagascar. The APG II system, of 2003, does recognize this family and assigns it to the order Caryophyllales in the clade core eudicots.
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 .
Trochodendron aralioides, sometimes colloquially called wheel tree, is a flowering plant and the sole living species in the genus Trochodendron, which also includes several extinct species. It was also often considered the sole species in the family Trochodendraceae, though botanists now include the distinct genus Tetracentron in the same family. T. aralioides is native to Japan, southern Korea and Taiwan. Growing in lower temperate montane mixed forests in Japan, and broad-leaved evergreen forest in the central mountain ranges and Northern parts of Taiwan.
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.
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.