Commelinaceae

Commelinaceae is a large and diverse family of flowering plants. It is often called the dayflower or spiderwort family. This group is one of five families within the order Commelinales. It is the largest family in that order. Currently, scientists have identified about 731 known species. These species are organized into 41 different genera. Many of these plants are herbaceous, meaning they have soft stems. Because they are often colorful, people cultivate many species as ornamentals.

The plants in this family show incredible variation in their physical forms. This variation in morphology is exceptionally high among all flowering plants. Most members are terrestrial, meaning they grow in the ground. However, the genus Cochliostema contains epiphytes, which are plants that grow on other plants. Most species are perennials that live for several years. A smaller number of species are annuals that complete their life cycle in one year. Some genera, such as Streptolirion and Aetheolirion, are even climbers.

One way to identify these plants is by looking at their leaves and stems. The leaves are arranged alternately along the stem. They may be arranged in a spiral or in two rows. The leaf blades are simple and entire, so they lack teeth or lobes. Many leaves are succulent, which means they are fleshy. A distinctive feature is how the leaves unfurl from a bud. This process is called involute, where the leaf margins roll inward as they emerge.

The leaves also form a closed sheath at the base that surrounds the stem. This is similar to grass, but these sheaths do not have a ligule.

The flowers of Commelinaceae are famous for being ephemeral. This means they are very short-lived, often lasting only a day or even just a few hours. After they open, the flowers may deliquesce, or melt away. Because they are so short-lived, many species have specific flowering seasons. They may also flower at specific times of the day. This timing helps to isolate different species reproductively.

Interestingly, these flowers do not produce any nectar. Instead, they offer only pollen as a reward to pollinators. Some species even use deception to attract insects. They may use yellow hairs or broad anther connectives to mimic extra pollen. They might also use staminodes, which are sterile stamens that look like they contain pollen.

Flower structure in this family can be quite complex. The flowers can be actinomorphic, meaning they have radial symmetry like a star. They can also be zygomorphic, meaning they have only one plane of symmetry. Most species are hermaphroditic, containing both male and female organs. Some are andromonoecious, meaning they have both bisexual and male flowers on one plant. The single species Callisia repens is gynomonoecious, having both bisexual and female flowers. Other species are polygamomonoecious, possessing bisexual, male, and female flowers.

Each flower typically has three sepals and three petals. The petals are sometimes clawed, which means they narrow into a stalk at the base. There are almost always six stamens arranged in two whorls. These stamens show many different arrangements. In many genera, two to four of these are staminodes that do not produce pollen. The flowers often grow in an inflorescence called a thyrse. This structure is made of subunits called cincinni. These look like clusters shaped like a scorpion's tail along a central axis.

Taxonomists have long recognized this family. The APG III system, established in 2009, continues to recognize Commelinaceae. It places the family in the order Commelinales within the clade commelinids. Scientific analysis, such as the study by Burns et al. in 2011, shows that this is a monophyletic group. This means all members of the family share a single common ancestor. By studying DNA sequences from the plastid gene rbcL, researchers can map the evolutionary tree of these diverse plants.