The Cucurbitales are an order of plants with a cosmopolitan distribution, particularly diverse in the
tropics. Most are herbs, climber herbs, woody lianas or shrubs but some genera include canopy-forming evergreen
lauroid trees. Members of the Cucurbitales form an important component of low to montane tropical forest with greater representation in terms of the number of species. Although not known with certainty the total number of species in the order, conservative estimates indicate about 2600 species worldwide, distributed in 109 genera. Some of the synapomorphies of the order are: leaves in spiral with secondary veins palmated, calyx or perianth valvate, and the elevated stomatal calyx/perianth bearing 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, however taxonomists have not agreed on the exact placement of this family within the Cucurbitales. Over half of the known members of this order belong to the greatly diverse begonia family Begoniaceae, with around 1500 species in two genera. Before modern DNA-molecular classifications, some Cucurbitales species 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 remain unclear. The lack of knowledge about the order in general is due to many species being found in countries with limited economic means or unstable political environments, factors unsuitable for plant collection and detailed study. Thus the vast majority of species remain poorly determined, and a future increase in the number of species is expected. == Etymology ==