The Bower Vine, sometimes called Pandorea, has characteristics similar to petunias. It became popular in the 14th and 15th centuries as a trellis plant. The vine does well in both full and partial sun, and needs careful tending--particularly proper watering. Fertilizer is necessary to help the plant achieve its full potential.
The Calibracoa plant, also known as Million Bells and Lirica Showers, is fairly new to the gardening scene; the plant has been recognized only since the mid-1990s. This plant has tubular flowers, similar to petunia blooms, that grow on trailing stems. Calibracoa plants are about 1/4 the size of a standard petunia plant, so they are a good choice if you like petunias but have limited space. Million Bells can thrive in up to a 1/2 day of full sun.
Another flower with similarities to the petunia is the Katie Ruellia. Katie Ruellia blooms are tubular, but have a slightly more trumpet-like shape than petunias. They are also drought resistant, so you won't have a problem growing them in hot, dry climates.
The most popular flower in the Tecoma Stans family is the Gold Star Esperanza, which can grow up to 6 feet in height and 4 feet in width. With tubular blooms and an abundance of green leaves and vines, this plant makes a spectacular showing in front yard garden spaces. This plant can handle a lot of sun, but does require regular water and fertilization for optimal growth.