Blue is perhaps the rarest color among plants. Blue is not a common color in plant organs other than flowers which suggests that blue as a flower color has advantages for attracting pollinators that warranted its evolution in flowers. I did a search on the Internet to get a list of blue flowers. I found the following: African blue lily (Agapanthus africanus); Ageratum (Ageratum houstonianum); Clematis; Anemone; Bellflower (Campanula); Bluebell; Salvia; Ajuga; California lilac; Chinese plumbago; Columbine (Aquilegia bertolonii); Delphinium; Iris; Scaevola aemula 'Blue Wonder'; Gentian; Globe thistle; Grape hyacinth (Muscari armeniacum); Lavender (Lavandula angustifolia); Lesser periwinkle (Vinca minor); Lobelia; Nymphaea spp.; Morning Glory (Ipomoea tricolor); Moss Phlox (Phlox subulata); Passion flower (Passiflora caerulea) Penstemon (Penstemon heterophyllus) ; Petunia; Rosemary (Rosmarinus officinalis); Sweet pea; Verbena.

Some of these blue-blooming plants have made it to the ranks of Texas SuperStar plants http://plantanswers.com/superstar_listing.htm
The most recently added blue entries are Vitex http://plantanswers.com/vitex.htm
and Plumbago http://plantanswers.com/plumbago_best.htm
The great things about these two new Texas SuperStars are that they are both butterfly habitats and are also deer resistant. These plant selections join the first Texas SuperStar in 1989 which is the state flower, bluebonnet. Many of the salvias are blue including the 1997 SuperStar Salvia leucantha and the 2006 selection named 'Henry Duelberg' Salvia http://plantanswers.com/salvia.htm

In 1998, two blue selections were dubbed Texas SuperStars-they were blue verbena named 'Blue Princess' http://aggie-horticulture.tamu.edu/plantanswers/98promotions/march/march.html and Scaevola aemula 'New Blue Wonder' Fan Flower. The Fan Flower was later found to perform best when left in a container.

There are also a number of petunias which have a blue color. In 1999, the Mother of all modern-day petunias was introduced as a Texas SuperStar under the name of V.I.P. (Violet In Profusion or Very Important Petunia)
This V.I.P. petunia is native to South America. The flower is violet colored and the plant is heat tolerant and low spreading. The plant is known for its profusion of small bell-shaped violet colored flowers. In 2001, a V.I.P. offspring named after the then First Lady of Texas, Laura Bush, became a Texas SuperStar plant. 'Laura Bush' petunia offers just as many colorful blooms but the blooms are twice as large and the plant has larger, darker green foliage which serves as a background to showcase the spectacular floral display. To date, it is the only flower in the world to be named for the First Lady of the United States, Laura Bush. This petunia from San Antonio has been planted at the Whitehouse for the past several years-wonder why?
http://plantanswers.com/petunia_bush.htm

Larkspur (Consolida ambigua)
http://aggie-horticulture.tamu.edu/plantanswers/98promotions/January/january.html and all of its Delphinium relatives have blue flowers in their genetics. Ruellias (Mexican petunias or Ruellia brittoniana) such as the 'Katie Dwarf' Ruellias which were SuperStars in 2002 have a light blue variety as well as a pink and white. A Texas SuperStar which will be promoted in 2007 is a beautiful blue flowering plant named Duranta repens. http://plantanswers.com/duranta.htm

A blue Hyacinth means Constancy; a blue Violet means Watchfulness, Faithfulness, I'll Always Be There in the Language of Flowers at: http://plantanswers.com/language_flowers.htm

Which is your favorite blue flower?