Overview
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 approximately 2.600 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 identifying 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 8 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 having 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 in long time isolated areas.
The order Cucurbitales is composed by 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 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 forest. The genus Dendrosicyos with the only species cucumber tree, is adapted to arid semi desert 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 by to be 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 know are in the great diverse Begonia group of Begoniaceae with 2 genera, and 1500 species. Because of the lack of worldwide knowledge about the order in general, very little is known about the order diversity. The knowledge of this order to national level, is that to be expected in countries with limited economic means with the vast majority of species indeterminate or even poorly determined. Therefore an increase in the study of order, at national level, is of utmost importance for the progress of the systematics of the order in general. 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 eight families of cucurbitales order, was assigned to orders as diverse as Ranunculales, Malpighiales, Violales, and Rafflesiales. Early molecular studies revealed several surprises, such as the non-monophyly of the traditional Datiscaceae, including Tetrameles and Octomeles, but the exact relationships among the families remained unclear.
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