Commelina

Commelina is the largest genus in the family Commelinaceae. The 18th-century Swedish naturalist Carl Linnaeus named the genus for two Dutch botanists, Jan Commelijn and his nephew Caspar, with each one symbolizing one of the two showy petals of the species Commelina communis. These plants are herbs that can be either perennial or annual. Their flowers are zygomorphic (having only one plane of symmetry), and the flower stalks are surrounded by modified leaves called spathes, which often contain a mucilaginous liquid.

Each spathe holds one or two scorpioid cymes; the upper cyme may be reduced or contain one to several male flowers, while the lower cyme bears several flowers. All species have leaves arranged alternately. The Asiatic dayflower (Commelina communis) is likely the most familiar species in the West, growing as a common weed in parts of Europe and across eastern North America. Several species, including Commelina benghalensis, are eaten as a leafy vegetable in Southeast Asia and Africa.

The roots are usually fibrous, though sometimes tuberous or rhizomatous. Leaves are arranged in two ranks or spirally, and may have a petiole or lack one; in the bud, the leaf is folded with inrolled margins or in a supervolute pattern. The inflorescence is terminal and often appears opposite a leaf at the node of a new axillary stem. It consists of one or two cincinni (scorpioid cymes), which are monochasia where lateral branches alternate sides.

The distal cincinnus may be vestigial or bear one to several male flowers; the proximal cyme is always present and multi-flowered. The folded spathe may have completely separate margins or be fused at the base. Flowers grow on pedicels and are strongly zygomorphic.

Bracteoles sometimes support the pedicels but are usually absent. Flowers are either bisexual or male. There are three unequal sepals, which may be free or have the two lateral ones fused. The three petals are free and unequal: the two upper ones are larger and clawed, while the lower petal is smaller and often a different color.

Flower color is most often blue, but also lilac, lavender, yellow, peach, apricot, or white. There are three stamens and two to three staminodes (infertile stamens), all with free, hairless filaments. The staminodes are positioned posteriorly and have antherodes with four to six lobes. The stamens are anterior and longer than the staminodes; the middle stamen differs in size and shape from the lateral two, and when a central staminode is present, it also differs from the others.

The ovary has two or three chambers, each containing one or two ovules. The fruit is a capsule, typically with two or three chambers (rarely one), and opens by two or three valves. Each chamber may hold one or two seeds, or none. The seeds are arranged in a single row, with a linear hilum and a lateral embryotega.