Climbing dayflower

Appearance

"Commelina diffusa" is typically an annual herb, though it may be perennial in the tropics. It spreads diffusely, creeping along the ground, branching heavily and rooting at the nodes, obtaining stem lengths up to 1 metre. Pubescence on the stem is variable and ranges from glabrous to hispidulous, which can occur either in a line or throughout. The leaf blades are relatively variable, ranging from lanceolate to ovate, with proximal leaves tending to be more oblong. They measure 3 to 12 cm in length by 0.8 to 3 cm in width. North American populations tend to have smaller leaf size, typically measuring 1.5 to 5 cm, by 0.5 by 1.8 cm. The leaf apex is acute to acuminate. The leaf surface can be either glabrous or hispid. The leaves are subsessile with a leaf sheath striped with red and covered with hispid pubescence.

The flowers are arranged into cincinni, or scorpioid cymes. This is a form of a monochasium where the lateral branches arise alternately on opposite sides of the false axis. There are typically two cincinni present, with the lower cincinnus bearing 2 to 4 flowers, while the upper cincinnus has one to several flowers. The upper cincinnus is generally exerted on specimens with larger spathes, but it may be included in specimens with smaller spathes. The upper cincinnus bears only male flowers and has a longer peduncle, while the lower cincinnus bears bisexual flowers on a shorter peduncle. The pedicels supporting single flowers, and later the fruits, are thick and curved and measure about 3 to 5 mm. The membranous sepals are inconspicuous at only 3 to 4 mm in length. The petals are blue, though may be lavender in rare cases. The upper two petals measure 4.2 to 6 mm. The anther connective of the centre-most stamen has a broad transverse band of violet. The spathes are solitary, borne on a peduncle and typically falcate with a cordate to rounded base, acuminate apices and can be either glabrous or hispidulous beneath. They usually measure 0.8 to 2.5 cm long, but may be as short as 0.5 cm and as long as 4 cm. They are typically 0.4 by 1.2 cm wide, but may be up to 1.4 cm long. Their peduncles are usually 0.5 to 2 cm long and rarely up to 2.9 cm. Flowering occurs from May to November.

The fruit is a capsule which has three locules and 2 valves. It measures 4 to 6.3 mm long by 3 to 4 mm wide, though it may be as narrow as 2.1 mm. They contain five brown seeds that are 2 to 2.8, rarely up to 3.2 mm long, by 1.4 to 1.8 mm wide. They are deeply reticulate. The chromosome number is 2n = 30.

Distribution

The plant is present in tropical and subtropical locations worldwide. It can be found throughout much of southern China, specifically in the provinces of Guangdong, southwestern Guangxi, southwestern Guizhou, Hainan, southeastern Xizang and southeastern Yunnan. In Japan the plant has been reported from Yakushima off Kyūshū and is also present in the Ryukyu Islands from Amami Ōshima southwards.

It is native in parts of the West Indies, including much of Puerto Rico and several of the Virgin Islands such as Saint Croix, Saint Thomas and Tortola. It has also been introduced to the southeastern United States where it is present from Maryland in the north, west to Missouri and south to Texas and Florida. It has also been introduced to Hawaii, where it is a common and quickly spreading weed. The variety "C. diffusa" var. "gigas" has been introduced to Florida.

In China it can be found from sea level up to 2100 metres, and is typically associated with forests, thickets, stream banks and other open and humid habitats. In the West Indies it is a common weed that is especially associated with roadsides, moist ditches and waste places and it can be found from sea level to 1050 metres. In the United States it is also typical of disturbed locations, such as gardens, cultivated areas and lawns, but can also be found in woods and other moist situations.