Members of the massive legume family, poinciana trees display pinnately compound, feathery leaves and bear colorful five-petaled blossoms. Historically, poinciana trees were in a botanical genus named Poinciana, which taxonomists consider defunct. Those trees in that old genus retained it as a common name, even though they exist today in botanical genera of different names. All are tropical trees that grow their best in full sun conditions in regions where winters don't receive frosts and freezes.
Some horticulturists regard the royal poinciana (Delonix regia) as the most beautiful flowering tree in the world. A partially deciduous tree from Madagascar, it drops leaves in the tropical dry season. The royal poinciana is grown worldwide in tropical regions, where it is also called flamboyant or fire tree. It matures 30 to 50 feet tall. Anytime from late spring to midsummer, the branch tips bear large clusters of orange-red flowers all across the tree canopy. Each blossom comprises five club-shaped or clawlike petals, the uppermost a bit larger with speckles of white. Large dark brown seed pods follow and persist on branches. Grow it in U.S. Department of Agriculture plant hardiness zones 10 and warmer.
Also called pride-of-Barbados or peacock flower, the dwarf poinciana (Caelsalpinia pulcherrima) hails from Mexico and Central America. Also grown all across the tropics today, this large shrub to small tree matures 8 to 20 feet tall with open, floppy and thorny branches. The flower spikes are upright and loosely branched, occurring on branch tips. Each blossom is usually dark orange-red with petal edges marked in yellow. It blooms anytime temperatures are warm from spring to late fall. Since plants readily grow from seed, genetic variation is widespread, with some trees bearing fully yellow or reddish violet-pink blossoms. Grow it in USDA zones 9 and warmer.
The Mexican poinciana (Caesalpinia mexicana) looks very much like the dwarf poinciana in form and size, growing up to 20 feet tall. By contrast, the Mexican poinciana lacks thorns on its branches and always yields yellow flowers in upright spikes. The flowers never occur heavily, but practically any time of year a branch bears some blooms. Native to the hilly country in northern Mexico, grow Mexican poinciana in USDA zones 9 through 12.
None of the three poinciana trees are grown for food, and rarely as firewood, perhaps when other large tropical trees are no longer available. The pods of royal poinciana are used as fuel in the Caribbean. All are revered as ornamental trees. The royal poinciana's size works well as a shade tree along avenues or spacious parks and gardens. The smaller stature of the other two species finds them used in a mixed shrub border or as a small accent tree near a house or small garden space.