Commelina communis aka Dayflower

Commelina communis, or Asiatic dayflower, belongs to the spiderwort family. This annual grows through summer and spreads across the ground. Its native range runs from eastern Europe through Asia. It reaches Japan and parts of mainland Southeast Asia. It has spread into eastern Canada and much of the United States. In Japan, it grows in damp grassland, fields, and roadsides.

Plants stand upright or creep, forming patches from fibrous roots. Garden plants reach 1–3 feet (0.30–0.91 metres) tall. Their spread ranges from 2–10 feet (0.61–3.05 metres). Another source records stems of 0.82–2.30 feet (0.25–0.70 metres). The round stems feel smooth and have no hairs. They can root at joints and form new plants. Green leaves grow in an alternate pattern along each stem. Their shapes range from broad lances to eggs or slight hearts. Each leaf has smooth edges and parallel veins. A thin sheath wraps around the stem at its base.

Flowers appear from midsummer into early fall. Each opens in the morning and lasts just one day. Blooms measure about 0.04–0.08 feet (0.013–0.025 metres) across. They have three petals, with blue or blue-and-white colouring. Yellow anthers on the upper, sterile stamens draw insects. The longer lower stamens are fertile. A green spathe sits beneath each flower. Bees visit the blooms, and insects pollinate the plant. Seed capsules follow the flowers and mature in fall. Each capsule has two chambers, each holding two seeds. The brown or black seeds have rough surfaces.

Partial shade suits this plant best, though it accepts full sun. It prefers fertile, moist loam or soil with some sand. Sources also recommend good drainage, leaf mould, and a sheltered site. It can cope with soil that dries out at times. NC State lists USDA zones 5a through 8a. Growth is fast, and routine care needs are low. Some gardeners use it as ground cover in damp woods. Its long bloom season adds colour through summer and fall.

Its spread can crowd out other plants in good conditions. Some US states class it as invasive, but North Carolina does not. Resistance to herbicides can make control hard. NC State reports no known diseases or insect pest problems. Deer favour its leaves, and six-spotted beetles also eat them. People grow it as a vegetable in China. The leaves, flowers, and young shoots can be eaten raw or cooked. They taste sweet and have a slippery texture. Sources report no known hazards, rather than proven safety for pets. Traditional medicine uses include gargles and preparations for fever and diarrhoea. Reports also describe antibacterial activity in plant extracts. The petals provide a blue dye used in Japan.