Juss. ex Bercht. & J.Presl
The Cucurbitales are an order of flowering plants, included in the rosid group of dicotyledons. This order mostly belongs to tropical areas, with limited presence in subtropic and temperate regions. The order includes shrubs and trees, together with many herbs and climbers. One of major characteristics of the Cucurbitales is the presence of unisexual flowers, mostly pentacyclic, with thick pointed petals (whenever present). The pollination is usually performed by insects, but wind pollination is also present (in Coriariaceae and Datiscaceae).
The order consists of roughly 2600 species in eight families. The largest families are Begoniaceae (begonia family) with 1400 species and Cucurbitaceae (gourd family) with 825 species. The large families of Cucurbitales include several economically important plants. Specifically, the Cucurbitaceae (gourd family) are responsible for some food species, such as squash, pumpkin (both from Cucurbita), melons including watermelon (Citrullus vulgaris), and cucumber (Cucumis). The Begoniaceae are known for their horticultural species, of which there are over 130.
The Cucurbitales are an order of cosmopolitan plants with distribution, particularly diverse in the tropics. Most are herbs, climber herbs, woody lianas or shrubs but some genus are canopy evergreen lauroid trees. Cucurbitales form an important component of tropical forests from low to montane forests with greater representation in terms of number of species. Although not known with certainty the total number of species in the family, conservative estimates indicate about 2600 species worldwide, distributed in 109 genera. Compared to other plant families, the taxonomy of the family is poorly understood due to their great diversity, difficulty in identification, and reduced taxonomic work done on it.
The order Cucurbitales in the eurosid I clade comprises almost 2600 species in 109 or 110 genera in eight families, tropical and temperate, of very different sizes, morphology, and ecology. It is a case of divergent evolution. In contrast, there is convergent evolution with other groups not related due to ecological or physical drivers toward a similar solution, including analogous structures. Some botanical species are trees have similar foliage to the Lauraceae due to convergent evolution.
The patterns of speciation in the Cucurbitales is diversified in a high number of species. They have a pantropical distribution with centers of diversity in Africa, South America, and Southeast Asia. They most likely originated in West Gondwana and are 67–107 million years old, so the oldest split could relate to the break-up of Gondwana in the middle Eocene to late Oligocene, 45–24 million years ago, and reached their current distribution by multiple intercontinental dispersal events. One factor was product of aridification, others groups responded to favorable climatic periods and expanded across the available habitat, occur as opportunistic species across wide distribution; other groups diverged over long times in isolated areas.
The Cucurbitales comprise the families: Apodanthaceae, Anisophylleaceae, Begoniaceae, Coriariaceae, Corynocarpaceae, Cucurbitaceae, Tetramelaceae, and Datiscaceae. Some of the synapomorphies of the order are: leaves in spiral, secondary veins palmated, calyx or perianth valvate, elevated stomatal calyx/perianth with separate styles. The two whorls are similar in texture.
Tetrameles nudiflora is a tree of immense proportions of height and width; Tetramelaceae, Anisophylleaceae, and Corynocarpaceae are tall canopy trees in temperate and tropical forests. The genus Dendrosicyos, with the only species being the cucumber tree, is adapted to the arid semidesert island of Socotra. Deciduous perennial Cucurbitales lose all of their leaves for part of the year depending on variations in rainfall. The leaf loss coincides with the dry season in tropical, subtropical and arid regions. In temperate or polar climates, the dry season is due to the inability of the plant to absorb water available in the form of ice. Apodanthaceae are obligatory endoparasites that only emerge once a year in the form of small flowers that develop into small berries.
Half of the species known are in the greatly diverse begonia group of Begoniaceae, with two genera, and 1500 species. Because of the lack of knowledge about the order in general, very little is known about the order diversity. The increase in the number of species is expected for the genera, bringing an expected considerable increase in the total number of species of the family. Before DNA-molecular classifications, the species placed now in Cucurbitales order, were assigned to orders as diverse as Ranunculales, Malpighiales, Violales, and Rafflesiales. Early molecular studies revealed several surprises, such as the nonmonophyly of the traditional Datiscaceae, including Tetrameles and Octomeles, but the exact relationships among the families remained unclear.
Under the Cronquist system, the first four families (including Begoniaceae, Cucurbitaceae, and Datiscaceae), were placed in the order Violales, within the Dilleniidae, with the Tetramelaceae subsumed within the Datiscaceae. The other families were distributed throughout various orders. The present classification is due to APG III (2009).
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