Commelina communis L. - Asiatic dayflower

Classification Hierarchy
Kingdom Plantae
Subkingdom Tracheophyta
Superdivision Spermatophyta
Division Magnoliophyta
Class Liliopsida
Subclass Commelinidae
Order Commelinales
Family Commelinaceae
Genus Commelina
Species Commelina communis L.

USDA Plant Profile

As its name implies, the flowers of the Asiatic Dayflower last for only one day. Typically two or three flowers (which constitute an inflorescence) are produced in a folded, heart shaped, leaf-like bract (called a spathe). The spathe is attached by its peduncle to the main stem. After the first flower blooms, It shrivels up and the next flower in the bunch blooms. After blooming the flowers disappear but the fertilized ovary grows into the fruit from which seeds develop (see photos below).

This plant is easily identified to the Genus level by the two blue petals that look like mouse ears. However, there are other species in this Genus that look similar. If you take the link to the USDA Plant Profile (above), then click on "thirteen species" under the related taxa heading, the distribution maps show only two species occurring in Iowa - C. communis and C. erecta. If you are trying to identify a local (Iowa) plant, It is probably one of these two species. A casual identification could be made by comparing the physical characteristics of your unknown plant to those of C. communis and C. erecta and naming it after the one it most nearly resembles. However, because it is possible that one of the other 11 known species may have slipped into the local area unnoticed, a more rigorous identification would require comparing your unknown plant to herbarium specimens of each of the known species. The ultimate identification may include comparisons to the type specimen of the suspected species and even genetic analysis.

Additional references: 1, 2, 3, 4, 5.

Additional Images
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Gray's Manual of Botany 8th Ed. by M. L. Fernald offers extensive botanical information about individual species native to the U.S as well as the taxons to which they belong and keys to differentiate one from the other. As an example, here is how he describes first the genus Commelina; and secondly the species C. Communis (the keys have been omitted).

Commelina L. Dayflower. Flowers irregular. Sepals somewhat colored, unequal; the 2 lateral partly united. Two lateral petals rounded or reniform, on long claws, the odd one smaller. Stamens unequal, 3 of them fertile, one of which is bent inward; 3 of them sterile and smaller, with imperfect cruciform anthers; filaments naked. _ Often procumbent and rooting at the nodes. Leaves contracted at base into sheathing petioles; the floral one cordate and clasping, folded together or hooded, forming a spathe inclosing the flowers, which expand for a single morning and are recurved on their pedicel in bud and after wilting. Petals mostly blue. Flowering all summer. Ours all with perennial root, or propagating by striking root from he joints. Genus of trop. and warm-temp. reg. (Dedicated to the early Dutch botanists, Commelin, on account of the 2 showy petals and 1 less conspicuous petal, Linnaeus referring to the three botanists of that name, two of whom, Jan, 1629-1692, and Kaspar, 1667-1731, were conspicuous botanists, while the third “died before accomplishing anything in Botany”.

1. C. communis L. (growing in colonies). – Annual with slender roots and erect or decumbent and rooting bases; the stems and branches ascending or depressed, smoothish; leaves fleshy, with lanceolate or lance-ovate blades 4 -12 cm. long, the sheaths glabrous on margin and summit; spathes 1.5 - 3 cm. long, on peduncles 1 - 5 cm. long, round-cordate when opened out, petals clawed, ovate, with pale violet-blue blades, 1-1.5 cm. long, 3rd petal paler and smaller; lobed sterile anthers yellow; seeds rugose, 3.5-4 mm. long. – Dooryards, ditches, roadsides and groves, Mass. to Wisc., s. to N.C., Ala., Ark. and e. Kans. June-Oct. (Natzd. from Asia)