Asiatic dayflower

Appearance

The Asiatic dayflower is an annual herb with stems that are typically decumbent, meaning that they are prostrate at the base but become erect towards the tips, but some individuals may be simply erect. The diffusely branched stems tend to root at the basal nodes.

The pubescence on the stems is variable, but common patterns include a line of hair continuous with the leaf sheath, or they may be glabrous basally, meaning hairless, and puberulent towards the extremities, that is covered with fine hairs. The leaves are sessile: they lack a leaf stalk, also known as a petiole; or they may be subpetiolate, meaning they have very small petioles.

The leaf sheaths are cylindrical, sometimes striped with red, and typically glabrous, but usually have margins that are puberulent or pilose, meaning lined with fine, soft hairs. The leaf blades range from narrowly lanceolate, or lance-shaped, to ovate-elliptic, between egg-shaped and ellipse-shaped. They measure 3–12 cm by 1–4 cm wide.

The blades range from glabrous to puberulent and have scabrescent, or slightly rough, margins. Their tips are acute, meaning they come to a point quickly, to acuminate, meaning the point develops gradually. The leaf bases are oblique, or uneven.

The flowers are arranged on inflorescences called cincinni, which are also called scorpioid cymes. This is a form of a monochasium where the lateral branches arise alternately. The cincinni are subtended by a spathe, a modified leaf. The solitary spathes usually measure 1.2–3 cm long, but some may be up to 3.5 cm in length, while they are 0.8–1.3 cm tall, but sometimes up to 1.8 cm.

The uncurved spathes typically have a cordate, or heart-shaped, whitish base, which contrasts with its dark green veins. Their margins lack hairs, are somewhat scabrous, or rough, and are unfused, meaning they are distinct to the base. Their apices are acute to acuminate while the surfaces are glabrous, puberulent, or hirsute-ciliate, meaning with longer, shaggier hairs. The spathes are borne on peduncles, or stalks, that measure 0.8–3.5 cm and sometimes up to 5 cm long.

There are often two cincinni present, though the upper, or distal, cincinnus may be vestigial. The lower, or proximal, cincinnus bears 1 to 4 bisexual flowers and is nearly included in the spathe, while the upper cincinnus has 1 to 2 male flowers and is about 8 mm long.

The individual flowers are subtended by bracteoles that fall off early in development. The pedicels supporting single flowers, and later the fruits, are erect initially but curve when in fruit. They measure about 3–4 mm. The 3 concave, membranous sepals are inconspicuous, but persist after the fruit develops; the lateral pair are fused basally, measure only 4.5–5 mm long by 3–3.7 mm wide, and are elliptic and glabrous.

The lower sepal is lanceolate and about 4.5 mm long by about 2.2 mm wide. The 2 upper petals are blue to indigo in colour, while the much smaller lower petal is white. The upper two petals measure 9–10 mm long by 8–10 mm wide, while the lower petal is 5–6 mm long by about 6 mm wide. The 2 upper petals are composed of a claw about 3 mm long and a broadly ovate limb with an acute apex and a cuneate-cordate base.

Distribution

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 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 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 350 to 2,400 m 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.

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.