Most verbena plants are native to the tropical and subtropical regions of North, Central and South America, and some species are native to the Old World. More than 200 species of verbena make up the widespread and well-known flowering group of the Verbenaceae family. While some verbenas are annuals, most of them are perennials.
As perennial flowers, verbenas are regarded as very showy flowers that bloom continuously. As a group of hardy flowering plants, they are tolerant to heat and humidity, characteristic of their native climates.
There are three categories of verbenas, according to Dr. Jerry Parsons of the Texas Cooperative Extension and Greg Grant of Lone Star Growers. Annual verbenas are labeled "short-lived annual verbenas," and perennial verbenas are divided into "large-flowered, short-lived perennial verbenas" and "small-flowered, long-lived verbenas." The long-lived verbenas usually describe the hybrid varieties.
According to Bastyr University, common verbena, or vervain, (Verbena officinalis) grows throughout the Mediterranean area, North Africa, Asia and some parts of Europe.
Vervain is a perennial flowering plant that produces small lavender flowers, which emerge from its flowering spikes. Its flowers and leaves have been used in alternative medicine for several ailments, including headaches, PMS and indigestion.
It prefers full sun and grows in a range of soil types and acidity levels, but prefers moist, well-drained soil conditions. Also known as herb of the cross, herb of grace and in Chinese, ma bien cao, vervain can grow more than 3 feet tall.
Also known as blue vervain and swamp verbena, blue verbena (Verbena hastata) is a biennial that grows in moist fields throughout the United States and Canada. Blue verbena grows up to 5 feet tall and produces small blue to purple flowers on its branched, spike inflorescences from June through September. It grows in full-shade to full-sun exposure. Blue verbena has natural medicinal properties and is attractive to butterflies and birds.
Gray Vervain (Verbena canescens) is a perennial herb that grows up to 18 inches tall. Its purple or blue flowers bloom from April through October, and the plant requires full sun and moist-to-dry soil. This type of verbena gets its name from the grayish color of its leaves and stems.
Clover's vervain (Verbena cloverae) is native to the United States, and is also known as Verbena cloverae var. lilacina. It produces pale lilac to purple flowers that emerge along the plant's inflorescent spikes. It is primarily found in Texas and grows as a perennial herb or small shrub.