Austin’s Butler Hike and Bike Trail can be a great place to relax, burn calories or watch the nightly exodus of the Mexican free-tailed bats, all while surrounded by a lush panoply of plants. But when’s the last time you took a close look at the dome of trees above you while on your regular run, or at the verdant shrubs at your feet, growing in wild abandon down to the river’s banks?
The trail wasn't always so green. Its beautification was envisioned in the early 1970s by Lady Bird Johnson, Roy Butler (then Austin's mayor) and his wife, Ann, inspired by a balcony view of an idyllic path along the River Thames in London, according to the nonprofit Trail Foundation's website. Johnson, who had previously spearheaded several beautification efforts around the country, wanted to create a similar path in Austin along the Colorado River.
Flash-forward to today, and shorelines that were once muddy and barren now thrive with several species of native plants. Recently, Meg Inglis, Paul Montgomery and Edward Travis — all members of the Texas Native Plant Society — headed out to the eastern portion of the Butler trail to identify some of the common species that grow there. Want to go plant spotting yourself this weekend? What follows is an abridged list of some common plants visible along the trail, as identified by the members of the society. Unless otherwise stated, all plants are native to the area.
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Sugarberry/hackberry (Celtis laevigata). Sugarberry is a common tree throughout the southeastern U.S. that can grow up to 80 feet. It has thick, gracefully arching limbs that are grayish and resemble elephant trunks. The bark is covered in wartlike projections, as are the leaves, making this tree easy to identify. Warts on the leaves are caused by jumping plant lice, a type of insect related to cicadas. They lay their eggs inside a leaf, which causes the warts, or galls, to develop on the leaf’s surface, harboring the developing insects that feed on the sugar produced by photosynthesis. The trees don’t appear to be harmed much by this parasitic relationship.
Texas ash (Fraxinus texensis). This tree is well suited to Austin’s dry, hot conditions and is especially common on or near limestone outcroppings. The leaves turn a brilliant crimson hue in fall.
Cottonwood (Populus deltoides). This is a common tree near rivers and streams in several parts of Texas, from the Louisiana border all the way to Big Bend. These are big trees, reaching up to an impressive 130 feet. They tend to grow near water, because they use such massive amounts of it. A large tree can suck up more than 100 gallons of water per day. If you’re ever close to a cottonwood in early summer, you might be surprised to see what looks like a fine blanket of snow surrounding it. These are the seeds, which are attached to fine, cottonlike hairs that catch the wind and help disperse the seeds across long distances. The leaves are thick, shiny and roughly in the shape of a triangle, turning a bright yellow in fall.
Black willow (Salix nigra). No Central Texas stream would be complete without willow trees. They have long, slender leaves and flexible branches that often dip down to the water’s edge, creating a small, shady cove in which to shelter while kayaking. Willow trees contain a compound called salicin, which as far back as 2,000 B.C. has been used by various cultures to soothe pain. When ingested, salicin is converted into salicylic acid, the same substance used in aspirin.
Texas mountain laurel (Dermatophyllum secundiflorum). A small evergreen tree in the bean family with smooth gray bark that contrasts sharply with the dark green leaves. You might easily mistake this tree for a crepe myrtle, but unlike that tree, mountain laurels are native and grow in dry limestone soils west to New Mexico. They produce pendulous masses of purple flowers in the spring that ultimately develop into bean pods.
Anacacho orchid (Bauhinia lunarioides). Like the Texas mountain laurel, this is another small tree that might remind you of crepe myrtle at first, until you peek at the leaf, which looks like two leaves fused together in the shape of a butterfly. It produces abundant, fragrant white flowers in the spring that are similar in appearance to the flowers of some orchids, giving the plant its common name. The flowers attract bees and butterflies and later develop into bean pods.
Mulberry (Morus/Broussonetia). You’re likely to see more than one species of mulberry tree along the trail. These trees produce berries that are an important source of food for wildlife. Both red mulberry and Texas mulberry are native, but paper mulberry is a transplant from Asia. The latter can be identified by the brown markings on its bark that look almost like leopard spots. The leaves on all three species are conical but grow in different shapes; they might develop deep lobes that make them look like tridents. Leaves on a single tree can look very different from each other. Texas mulberry leaves feel like sandpaper on the top and bottom, while red mulberry leaves are only rough on the top side. Paper mulberry leaves are entirely soft.
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Boxelder (Acer negundo). Probably the only tree you’ll ever mistake for poison ivy, boxelder is a type of maple that commonly grows along streams and creeks, with leaves made up of three to five smaller leaflets, giving a strong resemblance to that pesky ivy. Like other maples, boxelders produce samara, a type of fruit with two long "wings" that cause the seed to spiral through the air when it detaches from its parent plant.
Carolina laurel cherry (Prunus caroliniana). Impress and terrify your friends with this common native plant. Laurel cherries are small trees that grow abundantly in dark understories. The leaves smell like maraschino cherries. That might make sense at first, given that it’s in the cherry family. But maraschino cherries only have the scent we commonly associate with them because they’re flavored with bitter almond oil. That oil contains a compound called cyanogenic glycoside, made up of a sugar and cyanide molecule. Laurel cherries have this, too. When exposed to oxygen, the sugar separates from the larger compound and gives the plant the sweet smell of cherries, while simultaneously activating the deadly cyanide molecule. In bitter almond oil, the cyanide is removed via processing, leaving behind only the sweet-smelling sugar. For this reason, no part of laurel cherries (or any other cherry tree) should be ingested.
Eastern redbud (Cercis canadensis). Native trees that were planted along the trail to add spring color, rivaling that of the cherry blossoms in Washington, D.C., where Lady Bird Johnson also started beautification efforts. This tree produces copious pink or purple flowers before it leafs out in the spring; the heart-shaped leaves turn vivid red and yellow in the fall.
Bald cypress (Taxodium distichum). These are large trees with an impressive ability to adapt to a wide variety of environments. Near bodies of water, such as streams, rivers or swamps, they often produce cypress knees from their roots, which bear a resemblance to the slender Tianzi Mountain peaks in China. These structures are thought to help oxygen get down to the roots, allowing the plants to respire even in waterlogged conditions. A healthy tree can live up to several thousand years. The oldest bald cypress, which grew in Florida, was burned down in 2012 and was estimated to be 3,500 years old. Bald cypress trees produce light green cones and lose their featherlike leaves in the fall, giving them their common name.
American sycamore (Platanus occidentalis). A large tree that often grows near bodies of water, such as streams and rivers. As the tree matures, the outer bark sloughs off in small fragments resembling puzzle pieces, leaving behind a bone-white inner bark that’s smooth to the touch. The tree produces soft, circular fruit made up of many small achenes (the "seeds" on the surface of strawberries are a type of achene). The achenes are attached to fuzzy hairs that help catch the wind and disperse the seeds away from the parent tree.
Mexican buckeye (Ungnadia speciosa). A small understory tree. Like eastern redbuds, these trees will bloom with lavender flowers in spring, usually before they produce leaves. One of the most distinctive features of this tree is the three-lobed fruit that contains large seeds. Once mature, it’s easy to break open the capsule, and the seeds will easily germinate if planted.
Jerusalem thorn (Parkinsonia aculeata). While not as common as most of the other plants on this list, Jerusalem thorn is well worth looking for. This small tree has green bark and long, slender leaves, with many smaller leaflets attached. During the spring and summer, it sports a profusion of yellow, scented flowers. But be careful: As the name suggests, this tree has thorns on both the trunk and branches. A large example of this tree can be found near MoPac Boulevard (Loop 1) on the south side of the river, and a few younger trees grow on the Shoal Creek peninsula.
Live oak (Quercus virginiana). There are several different species of oak that grow along the trail, but probably none as familiar as the live oak. These trees get very large, but instead of growing vertically, they have thick limbs that grow out in every direction, making them the perfect shade tree. They grow throughout the southeastern U.S., including Florida, where they’re able to weather some of the toughest hurricanes.
Pecan tree (Carya illinoinensis). Chances are, you’ve encountered this tree all over Austin. Pecans are in the hickory family and produce copious edible nuts that usually ripen and come off the tree in fall. The trees can become quite large and can often be found growing in flood plains, where they can withstand moderate amounts of inundation.
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Shrubs and vines
Turk’s cap (Malvaviscus arboreus). A plant you’ll see in relatively bright areas along several parts of the trail (there’s a large stand of them under MoPac on the north side of the river). This plant is a type of hibiscus. The flower petals are bright red and overlap in spirals that attract hummingbirds and butterflies and are reminiscent of the wavy lines in cupcake icing.
Poison ivy (Toxicodendron radicans). It’s very likely you’ve encountered this vine before. It might not be your favorite plant along the trail, but poison ivy is native and an important part of forest ecosystems in southeastern U.S. forests. The berries provide food for birds, while deer and insects (which don’t suffer from poison ivy rashes) consume the leaves. The plant produces a compound called urushiol in the leaves, stems and roots, and it only affects humans (and possibly other primates). If you ever try to get rid of poison ivy from your yard, it’s important never to burn any part of the plant, as that will aerosolize urushiol, allowing it to enter your lungs, which can potentially result in death. Poison ivy produces a compound leaf comprised of three leaflets, one at the top and two at the side (remember, leaves of three, let it be). Mangoes and cashews are in the same family as poison ivy and produce the same toxic compound, which is why some people have allergic reactions to mangoes. In cashews, urushiol is produced in something called an accessory fruit, which has to be removed before the seeds can be sold for consumption.
Trumpet creeper (Campsis radicans). A common vine throughout Central and East Texas, trumpet creeper can cover walls, trellises and trees in dense foliage in a variety of habitats. It produces large, conspicuous red flowers, which you can see dotting the treeline throughout much of the trail. The fruits resemble cigars, especially when they turn brown right before opening.
Mustang grape (Vitis mustangensis). A grape vine native to the southern U.S. Like other grapes in the area, the vines can get quite large, forming woody "trunks" called lianas. The grapes have been used to make mustang wine since the 1800s.
Alamo vine (Merremia dissecta). This vine is a type of morning glory, but unlike its relatives, it opens its flowers under the head of the midday sun, then closes them before sunset.
Giant ragweed (Ambrosia trifida). Like poison ivy, ragweed’s infamous reputation often precedes its identification. It’s a weedy plant that grows in bright, open spaces, such as near Zilker Park on the south side of the river. In spring, these plants produce millions of pollen grains, to which many people are highly allergic.
Horsetail (Equisetum). It might surprise you to learn that this spindly plant is a fern. You’ll find it growing in dense stands in some of the more natural areas of the trail, such as near Interstate 35 on the north side of the river. These plants are usually found in aquatic environments and are hollow inside to allow oxygen to reach the roots. At first look, it appears that these ferns are made up entirely of leafless stems, but if you make a close inspection of the "joints," you’ll see what look like curved pillars arranged in a row, which are the modified leaves of this plant. While they might not look like much today, horsetails were once one of the world’s first trees, and they were one of the dominant plants in the swamps of the Carboniferous Period, long before the dinosaurs. When you start up your car, chances are you’re using fossilized horsetail ferns to reach your destination.
Ball moss (Tillandsia recurvata). The southeastern U.S. is famously covered in the dangling fibers of Spanish moss, which look like old men’s beards. And while we might not have these long, pendent tree decorations in Austin, we do have a closely related species, sometimes called ball moss. These plants can commonly be found growing in the canopy of live oaks. But these plants are neither Spanish nor a type of moss. They’re actually bromeliads, a type of plant closely related to pineapples. And don’t worry about those live oaks: Spanish moss obtain their own water and nutrients and don’t harm their host trees.