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"Commelina communis" was first described in 1753 by Carl Linnaeus in the first edition of his "Species Plantarum", along with eight other species in the genus. The plant serves as the type species for the genus. The scientific name "Commelina" was chosen based on the Asiatic dayflower. Linnaeus picked the name in honour of the Dutch botanists Jan and Caspar Commelijn, using the two large showy petals of "Commelina communis" to symbolise them. A number of names given to plants thought to be different species have fallen into synonymy with the Asiatic dayflower. Albrecht Wilhelm Roth created the first such synonym, "Commelina polygama", in 1790. Wenceslas Bojer described what he believed were two new species, "Commelina barabata" and "Commelina salicifolia", in his work "Hortus Mauritianus", both of which were quickly found to be identical to "C. communis". Karl Sigismund Kunth created the synonym "Commelina willdenowii" in 1841. Finally, Korean populations of the species were named under the synonym "Commelina coreana" in 1910 by Augustin Abel Hector Léveillé.
Several varieties have also been named. "Commelina communis" var. "ludens" was created by C.B. Clarke after demoting it from the full species status in which it was placed by Friedrich Anton Wilhelm Miquel in 1861. The variety is distinguished by its darker flowers, antherodes with central maroon spots, less well developed distal cymes that usually do not produce a flower, and spathes that are proportionally broader. Jisaburo Ohwi's Flora of Japan also treats the variety as geographically distinct, stating that it is restricted to mountainous areas. This variety is still accepted by some workers, but others, such Robert B. Faden, consider it impossible to consistently separate from the type variety. Another variety, "C. communis" var. "hortensis", which was named by Tomitaro Makino and is apparently a cultivated variety which originated from "C. communis" var. "ludens" in Japan, is also accepted by some botanists. It differs in having larger showy flowers which are used to produce a dye (see "Uses" section below). A variegated form called "C. communis" var. "ludens" f. "aureostriata" named by Frank C. MacKeever in 1961 is known to occur randomly throughout much of the species' range.
Distribution and habitat.
The plant's native distribution includes much of East Asia and Southeast Asia. Country by country, it is found in China, Taiwan, Japan, Korea, the Russian Far East, Cambodia, Laos, Malaysia, Thailand, India, Iran and Vietnam. Within China it is found in all provinces except Qinghai, Hainan, Xinjiang, and Tibet. In Japan the plant is found throughout the bulk of the country from Hokkaido south to Kyūshū. In Russia the Asiatic dayflower is found naturally on Sakhalin as well as in the Far East in areas surrounding the Ussuri River.
The species has been introduced to much of Europe and eastern North America. On the former continent it is now found from Central Europe well into western Russia. Specifically it is known from Italy north to Switzerland, east through the region encompassing the former Yugoslavia, east into the regions around the Black Sea including Romania, the Moldavia Region, and Ukraine but excluding Crimea, north through the Dnieper Basin into Belarus and Russia, continuing east into the regions surrounding the Don River and the Volga River south to their intersection at the Volga-Don Canal and north to the regions around Lake Ladoga and Lake Ilmen, and farther east to the regions of the Ural River and the Kama River. It is also found in the Czech Republic and Slovakia. It is present in the provinces of Ontario and Quebec in Canada, and in most of the eastern and central American states from Massachusetts and New York state in the northeast, west to Minnesota and south through the Great Plains to Texas and east to extreme northern Florida in the United States.
Within its native distribution, the plant is most typical of moist, open places, including shady forest edges and wet areas of crop fields, orchards, ditches, and roadsides. In Taiwan, it can be found from elevation. In areas where the Asiatic dayflower is an introduced weed it is most common in waste places, but also along the edges of fields, woods, and marshes, and occasionally penetrating into woods.
Ecology.
The Asiatic dayflower is considered an invasive weed in many areas where it has been introduced. In the United States, the Virginia Department of Conservation and Recreation, for example, categorises the species as "occasionally invasive" in its "Invasive Plant Species of Virginia". This means that the plant will "not affect ecosystem processes, but may alter plant community composition by outcompeting one or more native plant species". The species is typically limited to disturbed sites, whence it spreads relatively slowly. Within its native range in China it is also sometimes considered a pest, especially in the northeast of the country where it has caused economically significant agricultural damage in orchards.
The Asiatic dayflower has been used in pollination studies concerning the behaviour of plants in relation to their pollinators. One important experiment tested the hypotheses that floral guides (i.e. various patterns and colours on anthers and petals) simultaneously promote pollinator visitation and prevent visits where the pollinator fails to come into contact with the stigma or anthers, termed pollen theft. As the flowers of the Asiatic dayflower lack nectar, they offer only pollen as a reward to their visitors. To attract pollinators, the plant has three types of brightly colored floral organs: the large blue petals, fertile yellow anthers, and infertile yellow antherodes that lack pollen. When the infertile antherodes were experimentally removed in natural populations, the number of total floral visitor landings was reduced, supporting the hypothesis that these infertile anthers essentially trick their pollinators into believing they offer more than they actually do. When the central, bright yellow fertile anther was removed, leaving only two brown fertile anthers, the frequency of legitimate flower landings decreased, meaning that the visitors were not pollinating the flowers, suggesting that floral signals also prevent "theft", or visits where the pollinators take pollen, but do not place any on the stigma. Thus both the fertile anthers and the infertile antherodes were shown to play an important role in both increasing visitor landings and orienting floral visitors toward a landing point appropriate for pollination.
Recent studies have shown that wild Asiatic dayflower populations found growing on copper mine spoils in eastern China exhibited very high concentrations of copper within the plants, the highest in the 48 species tested. "Commelina communis" had sequestered some 361 mg/kg of copper, while the plant with the next highest concentration, "Polygonum macrathum", had 286 mg/kg. Five of the species examined, including the Asiatic dayflower, also showed high concentrations of other metals such as zinc, lead, and cadmium. The results suggest that the Asiatic dayflower is a good candidate for copper mine spoil revegetation and phytoremediation.
Ten species of fungi have been found on the Asiatic dayflower, four of which can infect the plant, while 12 species of insects are known to be associated with it. Two of the fungi, "Kordyana commelinae" and "Phyllosticta commelinicola", are thought to be host specific with the Asiatic dayflower. Of the ten fungi seven are Basidiomycota and three are Ascomycota. Nine of the 12 insects associated with the plant are beetles, seven of which are in the genus "Lema", while the other two are in the families Hispidae and Pentatomidae. The remaining three insects include one species of moth, "Pergesa acteus", and two true bugs, namely "Aphis commilinae" and "Aeschrocoris ceylonicus". Important pollinators include the Asian honeybee, "Apis cerana", syrphid fly, "Episyrphus balteatus", and the bumble bee species "Bombus diversus".
Uses.
Medicine and food.
 In China it is used as a medicinal herb with febrifugal, antipyretic, anti-inflammatory, and diuretic effects. Additionally, it is also used for treating sore throats and tonsillitis. Recent pharmacological investigations have revealed that the Asiatic dayflower contains at least five active compounds. One of these, p-hydroxycinnamic acid, shows antibacterial activity, while another, D-mannitol, has an antitussive effect. In China and India the plant is also used as a vegetable and fodder crop.
Pigment and dye.
In Japan there is a sizeable dye industry devoted to the plant. The purported variety "Commelina communis" var. "hortensis", which is apparently a cultivated form of another putative variety, namely "Commelina communis" var. "ludens", is grown for its larger petals which yield a blue juice used in manufacturing a paper called "boshigami" or , which is the famous product of the Yamada village in the Shiga prefecture. The paper is usually resoaked, allowing the pigment to be reabsorbed in water for use as a dye. The dye, also referred to as "aigami", but also as or , is composed primarily of malonyl awobanin and was used extensively as a colorant in 18th and 19th century woodblock prints in Japan, especially during the early Ukiyo-e era. The colorant is known to have been used by several famous Ukiyo-e artists such as Torii Kiyonaga. However, "aigami" fades to a greenish yellow in a matter of months when exposed to sunlight. As a result, the color was eventually replaced by imported Prussian blue, a much more stable colour with its first commercial appearance in 1829 in the work of Keisai Eisen. The plant is also grown for its dye in northern China. Additional uses of the colourant include making preparatory designs on cloth before dyeing with other pigments.
Commelinin is the blue pigment from the flowers of "C. communis", is a metalloanthocyanin. It is a complex of 4 Mg2+ ions chelating six anthocyanin molecules.
Plant physiology and development.
"Commelina communis" is also used as a model organism in plant physiology and plant development to a limited extent, especially in relation to stomatal physiology and the biology of pigmentation development. For example, the blue pigmentation of Asiatic dayflower petals was shown to consist of a large complex of six anthocyanins, six flavones, and two associated magnesium ions, demonstrating that supramolecular complexes of several copigments and chelated metals often determine colour. Other research on the plant has helped to explain photoreceptor systems in plants such as their stomatal responses to blue light versus red light spectrums, abscisic acid perception and its role in cell signaling, particularly concerning the chemical's role in stomatal function, the role of vanadates in inhibiting stomatal opening, and the necessity of calcium in stomatal closure, among other topics. Its widespread use in stomatal studies is due to the fact that the leaves produce exceptional epidermal peels that are consistently one cell layer thick. This same quality makes the plant popular for use in laboratory exercises in higher education for demonstrating stomatal function and morphology. Guard cell turgor pressure and its regulation in the opening and closing of stomata is particularly easy to demonstrate with the Asiatic dayflower.