Commelina

Lore & Background

Plants in the genus are perennial or annual herbs with roots that are usually fibrous or rarely tuberous or rhizomatous. The leaves are distichous or spirally arranged with blades that either lack or have a petiole. The inflorescences are terminal and often leaf opposed, composed of one or two scorpioid cymes enclosed in a folded spathe that is often filled with a mucilaginous liquid. The flowers are strongly zygomorphic, with three unequal sepals and three free, unequal petals, the two upper ones being larger and clawed while the lower petal is typically reduced and often differs in color. Flower color is most typically blue, but lilac, lavender, yellow, peach, apricot and white also occur.

Reader's Guide

Its common name 'dayflower' reflects the ephemeral nature of its blooms. The genus was named by Carl Linnaeus to honor the Dutch botanists Jan Commelijn and his nephew Caspar, with each representing one of the showy petals of Commelina communis. The Asiatic dayflower (Commelina communis) is probably the best known species in the West, occurring as a common weed in parts of Europe and throughout eastern North America. Several species, such as Commelina benghalensis, are eaten as a leaf vegetable in Southeast Asia and Africa. The genus exhibits diverse floral morphology, including zygomorphic flowers, scorpioid cymes, and spathes that may contain mucilaginous liquid. Its seeds are uniseriate with a linear hilum and lateral embryotega.

Did You Know?

• The genus Commelina was named by Carl Linnaeus for two Dutch botanists, Jan Commelijn and his nephew Caspar, with each representing one of the two showy petals of Commelina communis.
• Commelina tuberosa is native to Mexico but is now grown worldwide as an ornamental plant.
• The Coelestis Group of Commelina tuberosa grows to 50 cm (20 in) tall by 100 cm (39 in) broad and flowers in summer and autumn.
• In the wild, Commelina tuberosa is encountered in moist fields, open forests, or pine-oak forests.
• The species Commelina tuberosa is characterized by its purple-splotched spathes with free margins, bright blue petals of equal size, and tuberous roots.

Botanical Identity and Morphology

Commelina tuberosa is a herbaceous perennial belonging to the dayflower family, a lineage that has long captivated gardeners with its vivid floral displays. Native to Mexico, this species has since been cultivated as an ornamental plant across the globe. Its most striking visual features include spathes marked with purple splotches and edged with free, unfused margins, lending the flower a delicate, almost lacy appearance. The petals themselves are a brilliant blue, and notably all are of equal size, creating a symmetrical bloom. Beneath the soil, the plant develops tuberous roots, a trait that gives the species its specific epithet and provides a means of perennating through less favorable seasons. The inflorescence is structured as lower cymes bearing between four and ten flowers each. In terms of overall growth habit, Commelina tuberosa is a low-growing plant distinguished by long, narrow leaves that set it apart from its close relatives within the broader taxonomic group.

Taxonomic Ambiguity and the Tuberosa Complex

One of the most debated aspects of Commelina tuberosa's classification is its relationship to several closely related species. In some taxonomic treatments, particularly the Flora Mesoamericana, three additional species—Commelina coelestis, Commelina dianthifolia, and Commelina elliptica—are subsumed under the name C. tuberosa rather than recognized as independent entities. When botanists choose to maintain these as distinct species, the collective is commonly referred to as the "Commelina tuberosa complex," a label that acknowledges both their close evolutionary ties and their genuine morphological differences. The practical consequence of this taxonomic uncertainty is most visible in horticulture, where growers and nursery professionals tend to treat each member as a separate plant. The reasoning is straightforward: the species within the complex exhibit differing growth habits and leaf shapes, making them behave quite differently in the garden. For instance, C. tuberosa itself is characterized as a low-growing plant with long, narrow foliage, a profile that distinguishes it from its complex-mates and justifies separate cultivation recommendations.

Native Range and Wild Habitats

Commelina tuberosa is indigenous to Mexico, where it has evolved in a variety of natural settings across the country's diverse landscapes. In its native range, the species is typically encountered in moist fields, open forests, and pine-oak forests—environments that share a common thread of adequate moisture and partial to full light availability. These habitats suggest a plant that thrives where the ground retains water but is not waterlogged, and where dappled sunlight filters through a canopy of oaks and pines or where open woodland provides unobstructed warmth. Despite being a Mexican native, Commelina tuberosa is now cultivated as an ornamental plant worldwide, a testament to the appeal of its vivid blue flowers and attractive foliage in garden settings far removed from its original ecosystems. This global horticultural presence, however, does not obscure its identity as a species with deep roots in Mexican flora, and its wild populations continue to occupy the same moist, semi-forested niches that shaped its evolutionary history.

Cultivation and the Coelestis Group

For gardeners seeking a reliable summer and autumn bloomer, the Coelestis Group—a cultivar group derived from Commelina tuberosa—offers a proven ornamental choice. As a warm temperate plant, it has a clear vulnerability to cold: temperatures dropping below minus 5 degrees Celsius (23 degrees Fahrenheit) can prove fatal. In regions with cooler winters, this means the plant must be carefully lifted from the ground and stored indoors over the winter months before being replanted once the threat of frost has passed. In terms of siting, the Coelestis Group performs best in a sunny or partially shaded location that is sheltered from harsh winds. Its flowering period spans the warm months, making it a dependable source of color from midsummer through autumn, and its manageable size keeps it from overwhelming smaller garden spaces.