Common names for plants usually come from an outstanding feature rather than scientific facts. Orchid trees Bauhinia are a prime example—those are not true orchids adorning the branches. While their five-petaled flowers do indeed look like orchids, these plants are members of the Fabaceae family, along with peas and beans. To really appreciate these trees, look past the flowers; from shade and shelter to soil health, the beauty of orchid trees extends far beyond their stunning blossoms.
The majority of orchids are epiphytes—plants that grow on another plant. They use the plant, usually a tree, as an anchor site, but they don’t take nutrition from it or harm it in any way. Orchid trees, however, stand on their own and have their roots deeply in the ground, drawing moisture and nutrients from the soil. There are about 300 species of Bauhinia, which grow as trees, shrubs, or climbing vines, depending on the type—and not all of their blossoms resemble orchids.
The yellow orchid tree B. tomentosa has less orchid-like flowers. As the name implies, the blooms are usually yellow, but the plant sometimes puts out purple flowers. Then again, plants can surprise us; the yellow orchid tree near the rattlesnake habitat in the Zoo’s Elephant Odyssey produces pink and white flowers!
The flamboyant, five-petaled blossoms of Bauhinia plants are known as “perfect flowers,” because each individual bloom contains both female and male parts. Bauhinia are monoecious, defined as “single house,” since both sexes are in a single flower; as opposed to dioecious, which is “two houses,” since male and female flowers are separate. The flowers draw plenty of pollinators: hummingbirds, bees, butterflies, and more. Look closely at an orchid tree in bloom, and you’ll see a buzzing metropolis of “customers” that busily transfer pollen as they shop for nectar.
Although the structure of Bauhinia varies greatly by species—from stately tree to tall shrub to scrambling vine—they all have twin-lobed leaves. The bi-lobed structure of these leaves allow them to fold in half to reduce sunlight exposure and water transpiration, and slow photosynthesis when needed. This characteristic leaf shape brings us back to the name game. Taxonomic names are often derived from Latin or Greek root words, but not always. Carl Linnaeus, an 18th century botanist, zoologist, and physician, known as the “father of modern taxonomy,” chose the name Bauhinia for this plant to honor twin brother botanists, Caspar and Jean Bauhin. A twin-lobed leaf plant named for twin botanists!
Most people think of orchid trees as beautiful ornamental plants. In South America, however, white orchid trees B. forficata have a more practical use—and an equally practical name. They’re called “cow’s hoof” trees, because the double-lobed leaves resemble a cow’s hoof. Tea made from the leaves has long been used in traditional herbal medicine there to balance blood sugar and as part of a compress for snake bites.
Most members of this genus are fast growers. Tree-form specimens typically reach heights of 20 to 40 feet, and can be almost as wide as they are tall. At the other end of the spectrum are Bauhinia that have a shrub habit. You’ll find red orchid B. punctata (also known as B. galpinii) by the Kopje habitat in Africa Rocks at the Zoo. It’s a semi-deciduous, sprawling, wide-spreading shrub reaching 10 feet tall by 15 feet wide. In the summertime, this African native has a striking flush of brick-red or salmon-pink flowers.
If you live—or travel—through the southern US, you’re likely to see plenty of purple orchid trees B. purpurea, the most common type used in landscaping. Reaching 20 to 35 feet tall, this species dazzles viewers with pink or purple flowers that measure 2 to 5 inches in diameter. After flowering, a large number of 12-inch-long, woody bean pods appear and remain on the tree throughout the winter. Eventually, the pods pop open, flinging large seeds to a potential future home. The empty pods drop to the ground and can create quite a mess, but people are willing to tidy up in exchange for the show the flowers put on.
Considered by some to be the most striking of all Bauhinia, the Hong Kong orchid tree B. x blakeana is a cross between B. variegata and B. purpurea. Because it is a hybrid, it is sterile and does not produce seed pods. However, it is propagated from cuttings and widely available for landscape use. Its five-inch-diameter flower is the national symbol of Hong Kong—and Hong Kong Airlines uses “Bauhinia” as their call sign!
Orchid trees are popular in home and public landscapes, but some are facing survival challenges in their native ranges. Of the approximately 300 species of Bauhinia, the International Union for the Conservation of Nature has assessed 34 species and found that 11 are Endangered or Vulnerable, threatened by agriculture, logging, or livestock overgrazing. One, B. haughtii, is found only in coastal Ecuador, and just 30 wild-growing individuals remain in a protected area. However, specimens of this species have been cultivated at the Ecuadorean National Herbarium and the Missouri Botanical Garden, propagated by seeds, cuttings, and grafting on to other rootstock.
Appreciating orchid trees goes beyond their nectar-rich blossoms and arching branches that provide shade and shelter for wildlife. As legumes, the roots of these plants fix nitrogen (vital food for flora!) in the soil. It can be said that from root to crown, orchid trees are a boon for their habitat—and human landscapes!