Unique Trees of North Texas:

Mexican Plum

(Prunus mexicana)

By Wes Culwell

Every March, Mexican Plum trees proudly display their dainty white blossoms while they compete in early spring with maybe the more popular Redbud trees, as the Redbuds catch our eyes with their pinkish-purple blooms.  But with close inspection, we find that the Mexican Plum is really a beautiful senorita with her delicate and beautiful blossoms and a unique and wonderful bark.  Since neither of these trees grow as a monoculture, they can sometimes be found blooming in small groups together.  They are our first native trees to remind us that once again spring is here.

So, let’s look at this Texas native’s two most popular features: the flowers and fruit.  The flowers are fragrantly strong and sweet with white petals and about 1” in diameter and usually in more of a mass than redbud flowers. And of course, they bloom before any leaves are present.  The fruit then begins to grow in midsummer and matures in September.  The mature, purplish-red round plums are up to 1” and are edible and can be eaten fresh or used in jams and jellies.  However, one must beat the birds and mammals to the plums.

Although Mexican plum is known for its flowers, the bark is definitely unique and beautiful.  The bark is tight and smooth and a metallic gray when it’s very young.  As the bark matures, it becomes a wonderful brown that is exfoliating, papery and scaly.  Very mature trees have deeply furrowed and rough bark that often develops a spiraling grain.

The Mexican Plum will grow in sun or moderate shade.  This small tree may reach 20 feet tall and wide and is deciduous with alternate, simple leaves on sort of irregular branching of the twigs and limbs.  I can’t say with conviction that the leaves are attractive, but they are unusual.  The leaves have a felt-like feel on the upper side and during the growing season they appear coarse-looking and usually about 2-4” long.  Most of the time, the leaves are folded over at the edges and appear water deficient even though it is a drought tolerant tree.  But the leaves make a big come back in the fall with beautiful yellow and orange colors.

This tree is easy to grow in most locations and once established, it requires little water or fertilizer.  It can be a little difficult to transplant from the wild, but can be easily grown from seeds planted in the fall or after cold stratification.  From experience, you must protect them during the germination time period from squirrels who may like them more than acorns.  Propagation can also be done by stem or root cuttings.

 

This little Mexican maiden needs to be used much more as an ornamental tree in our landscapes.  It can be used as a great alternative to dogwood trees, especially in clay or alkaline soils and dry sites that are detrimental to other species such as dogwood.  The next time you think “This is a great place for a redbud,” try to remember this beautiful delicate bloomer.  If you have to plant a redbud, plant a Mexican Plum to go with it, you won’t regret it!

Unique Trees of North Texas:

Texas Ash

(Fraxinus albicans Buckey, formerly Fraxinus texensis)

 

By Craig Fox

Ash trees, particularly in Texas, are a hot topic of conversation in the arboriculture world. After the formal confirmation of Emerald Ash Borer (EAB) in Tarrant County, ash trees seem to be on everyone’s mind and rightfully so. Though not nearly abundant here as in the Midwest where EAB originated domestically, North Texas has a modest population (about 2-4% of the urban forest) of ash trees at risk to the destructive pest.

Perhaps the most common ash in the western Metroplex is Texas ash. Just as other members of the genus Fraxinus, they have opposite bud and branch arrangement and pinnately compound leaves. Texas ash typically feature five to seven leaflets (fewer than what is common for green or white ash) rounded in shape with possibly a slight point at the tip. They display excellent fall color in hues of purple, reds and oranges–usually in November–before shedding all their foliage. Texas ash have narrow samaras, or winged seeds, with wings that generally do not extend past the mid-point of the seed and which may persist through winter.

Though they may grow to forty feet tall or larger, most Texas ash in our area tend to be smaller, probably due to the thin, rocky soils they natively inhabit and their relatively short lifespan. Large concentrations can be found on fossiliferous limestone ridges through areas such as the Fort Worth Nature Center & Refuge, around Lake Worth and through areas near Aledo, Azle and Weatherford, though it does often appear elsewhere in the DFW region. They are often found intermingled with Texas red oak, eastern redcedar, post oak and cedar elm in our area. Texas ash may be single trunk or multi-trunk and frequently found in colonies. Ultimately, their native range spans from a few counties in Southern Oklahoma near the Arbuckle Mountains, along a thin band into North Central Texas, eventually skirting the Balcones Escarpment and crossing into Northern Mexico.

During leafless periods, ash species are notoriously difficult to differentiate. Texas ash have “C-shaped” leaf scars where the bud sits within the cup of the “C”, very much like the white ash to which they are closely related. In fact, some botanists believe that Texas ash is a subspecies of white ash (Fraxinus americana). The botanical name was changed to Fraxinus albicans Buckley from Fraxinus texensis to correct a complicated issue of proper nomenclature (I still tend to use texensis for obvious reasons).

 

The DFW Regional Champion can be found in Fort Worth’s historic Pioneers Rest Cemetery—a worthwhile visit for the history, if not the tree. Located just north of downtown at 620 Samuels Avenue, the tree is the lone example of its species within the grounds and is officially recognized by the City of Fort Worth as a heritage tree. The state champion tree is located within Lost Maples State Natural area in Bandera County. Curiously, American Forests claims that the National Champion Texas ash is perched just south of Lake Ontario near Rochester, New York—well outside its native range and far removed from what seems to be the preferred site conditions.

Fraxinus is the Latin word for “spear”, while the common name ash is derived from “aesc”, an Anglo-Saxon word. Norse mythology states that humans emerged from Yggdrasil, a great ash tree spanning the cosmos and that both Odin and Thor owned spears made from ash. Vikings were sometimes referred to as “aescling”, translating to “men of ash” for the spears their warriors carried. Planks for ships, oars and chariot axles were commonly made from ash timber. Today, the wood of ash trees is popular for use in tool handles and baseball bats due to its shock resistance. It is also popularly used to create flooring and millwork.

All Fraxinus species in Texas are believed to be susceptible to attack by EAB, but some research indicates that green ash (Fraxinus pennsylvanica) is the preferred host. The beetle, Agrilus planipennis, is native to East Asia where it is rarely problematic within its native range. Believed to be introduced into North America in the late 20^th century, the borer was formally discovered in Michigan in 2002. The confirmed location in Tarrant County occurred in 2018 along Ten Mile Bridge Road, just north of the Fort Worth Nature Center & Refuge. Due to the extensive activity and damage found at the site, it is believed that EAB was present, but undetected, in Tarrant County for several years prior to discovery.

Evidence of EAB occurs in the upper canopy first, which can be hard to detect, but an increase in woodpecker activity could help provide clues as the birds actively feed on the larvae. A thinning upper canopy and epicormic shoots near the base of limbs or along the trunk are also common symptoms.  After hatching from eggs laid in bark cracks and crevices, S-shaped galleries which gradually open in shape are created beneath the bark as the EAB larvae chews through the tree’s phloem. Due to the extensive feeding and destruction of cambium and phloem, the bark will eventually begin to peel, split, or fall away. After feeding and overwintering, the beautiful adult beetles emerge from the trees (probably from March through June in our area) creating a D-shaped exit hole approximately one-eighth inch in diameter. Once affected, ash trees decline quickly, often losing large limbs in the upper canopy. The tree’s death is caused by the widespread destruction of the phloem tissue supplying carbohydrates and dissolved nutrients.

 

For updates, additional information, or useful resources on EAB, please visit:

Texas A&M Forest Service:  https://tfsweb.tamu.edu/eab/

United States Department of Agriculture:  https://www.aphis.usda.gov/aphis/ourfocus/planthealth/plant-pest-and-disease-programs/pests-and-diseases/emerald-ash-borer

Bartlett Tree Experts Technical Report: https://www.bartlett.com/resources/technical-reports/emerald-ash-borer

Unique Trees of North Texas:

Live Oak

(Quercus virginiana or Quercus fusiformis)

 

By Eugene Gehring

You may be asking how one of the most popular and common tree species in North Texas could be considered unique. The fact that it is so popular and common is one of the reasons I think it is unique. Live oaks will grow in almost any soil type. Quercus virginiana (coastal or Southern live oak) is native from Virginia down the Atlantic coast to Florida and across the southern states to somewhere west of Houston. Quercus fusiformis (plateau or escarpment live oak) is native west of I-35 down into the hill country and North in a 3-5 county band to just north and west of Fort Worth. Live oaks are found in the transitional counties. Whether they are “Southern” or “Escarpment” is a good question. The primary morphological difference is the shape of the acorn. The escarpment live oak acorn is fusiform, or more constricted at the base. After 30 years working with live oaks, I still don’t have a clue what that means.

Live oaks are different from the other oak species in several ways. They are evergreen or semi-deciduous. They drop their leaves in February/March instead of the fall. Their leaves are simple nondescript ovals, 1-4” long with an entire margin. White oaks have rounded lobes, while red oaks have points or stipules on their lobes. Based on leaf morphology, live oaks fit more with the white oak group. Live oaks can be more than twice as wide as they are tall with long graceful branches. White oaks tend to be about as wide as they are tall, and red oaks tend to be taller than they are wide.

The wood of most oak species is ring-porous. They lay down different size vessels and cells depending on the season. Live oaks are diffuse-porous. There is not a seasonal variation in the size of the vessels or cells. One of the major differences between white oaks and red oaks is tyloses within the vessels of the wood. In white oaks tyloses occur naturally, while in red oaks they do not. That is why whisky barrels are made of white oak. Live oaks do not have tyloses naturally in their wood, putting them in the red oak group.

Unlike most oaks, live oaks are prolific at sprouting from their roots. This characteristic, along with readily forming root grafts, allows live oaks in a given stand to share their roots. This is one of the reasons live oaks are considered drought hardy. It is also why oak wilt is so devastating to live oaks. During the drought of 2011 – 12 I witnessed live oaks in the Hill Country that bloomed or tasseled in the spring of 2011, but did not leaf out until it rained in the fall of 2012.

Live oaks have a unique ability to adapt and grow in a variety of environments. The exception being they do not tolerate extended periods of saturated soils. They will grow in the 100 year flood plain, but not in areas subject to regular flooding or standing water. In the late 1990s, there was a flood event on Lake Travis where mature live oaks were almost completely submerged and survived because it was a short duration. The same event killed live oaks on Stillhouse Hollow Lake because the water was not lowered as quickly.

Live oaks are hardy to the 7b/8a zones of North Texas. I think the escarpment live oak is somewhat hardier than the Southern live oak. The 60 degree swing in temperature in January 2108 caused damage to the leaves on some live oaks in North Texas. They were not prepared for the extreme change in weather. When I first moved to the DFW metroplex, I was told there were live oaks with basal cankers caused by the cambium freezing during one of the cold winters in the 1980s.

Another unique characteristic of live oaks is that they will grow in almost any soil type. They thrive equally well in the sandy acidic soils of East Texas and the alkaline limestone based soils of Central Texas. Although they are not native to the heavy clays of most of North Texas, they grow and thrive there as well.

Climate change is probably responsible for the split between Southern live oak and Escarpment live oak. At a warmer period in time water covered a lot of North Texas as evidenced by ammonite fossils in Parker County. As the climate cooled and the water receded live oaks were pushed south and the split occurred.

Live oaks have long been valued as landscape trees. Some of the oldest planted can be found at Oak Ally Plantation in Louisiana.  They were thought to have been planted around 1710. In North Texas, they can be found in almost every neighborhood. Most of the older planted live oaks are probably Southern live oak because they would have come from nurseries in East or Southeast Texas. As the population in Central Texas increased, more tree nurseries were started in the 70s and 80s resulting in more escarpment live oak in the industry.  That is not to say there were not wild trees dug in Parker or Hood counties and planted in Fort Worth or Dallas. There were also nurseries, like O. S. Gray in Arlington, that may have grown escarpment live oak.

A little known fact is that live oak was used in the construction of the USS Constitution (“Old Ironside”). Live oak branches were used to form the ribs of the ship. They used the natural curves of the branches for added strength.

I have had a love/hate relationship in the more than 30 years I have worked with live oaks. I have seen them survive the extremes of drought, flood, tornadoes and hurricanes. I have seen them growing in practically solid rock, sugar sand, black gumbo clay, from East Texas to Midland/Odessa, from Lubbock to Houston to Corpus Christi. More than half of the trees in “The Famous Trees of Texas” are live oaks. The species has been witness to treaties, hangings, fights, marriages and everything in between. I think live oaks are unique because of their strength, adaptability, and mystic.

Unique Trees of North Texas:

Eve’s Necklace

(Styphnolobium affine)

 

By Susan Henson

This is a unique spring bloomer that has been underutilized in the urban landscape. It is an attractive small tree that can be used under power lines, grows well in shade or full sun, plus blooms pink, fragrant, and wisteria-like flowers in the spring (March, April or May). The seed pods look like the old pop string pearls which help provide year round interest. Could be used as a replacement for Crape Myrtle and creates an impact when grown alone. Eve’s Necklace is a legume and since discovering the roots lack nitrogen fixing bacteria the name was changed from Sophora affinis to the current Styphnolobium affine.

Eve’s Necklace has lustrous green leaves, scaly reddish brown bark, and a rounded crown with yellow hard, dense sap wood. The yellow sap wood is used to make yellow dye. It grows quickly when young and can grow to 6 feet from seed in 3 years. When planted in a sunny location it reaches 15 feet in height quickly and then crown becomes more rounded and the growth slows. When grown in dense shade will become spindly to the point of looking almost vine like reaching for the sun. It is related to the Texas Mountain Laurel (Sophora secundiflora) which is evergreen. Leaves are divided into 6 to 8 pairs of leaflets plus a terminal leaflet on a rachis up to 9 inches long. Leaflets are elliptic to oval averaging an inch long, with a rounded, indented, or pointed tip, with smooth margins, and a rounded tapered base.

This tree thrives in the North Texas area on clay, sand, or limestone but the area should be well drained. The tree is native to Oklahoma, Arkansas, Louisiana, North Central and Central Texas. Once established this tree is extremely drought tolerant and only requires occasional watering. Can grow to 35 feet but have never seen it grow above 20 to 25 feet in height. In the wild it is usually an understory tree but can be found growing in roadsides, prairies, plains, meadows, pastures and open woodlands. Though short lived at 25 years they are easy to grow from seeds or cuttings. The bark is rather thin so particular care needs to be taken to protect young trees from weed trimmers.

The National Champion resides in Real County and is 37 feet tall, 77 inch circumference, a spread of 47 feet and an index rating of 125. There are specimens planted in Fort Worth as street trees on the north side of Park Hill between University and McCart, Turner Park in Grand Prairie, the campus of SAF under the power lines along the coliseum parking lot, San Antonio Botanical Gardens. The specimen in San Antonio Botanic Gardens is named ‘Amy’ and has a dark burgundy flower. The flowers can range from white to burgundy but are usually a lighter pink. This tree should be planted more in the DFW area.

 

Unique Trees of North Texas:

Bois d’arc

(Maclura pomifera)

By Wendy Pappas

The Bois D’arc (aka: Osage Orange hedge apple, horse apple, “bodark”, monkey ball, bow-wood, yellow-wood and mock orange tree) originally had a native range of river areas in Oklahoma, Texas, Arkansas and in the Blackland Prairies and Post Oak Savannas. The native range overlapped the range of Osage tribe, which gives the tree one of its many names. Almost all of the names relate to the interesting fruit or strong wood. It has been naturalized throughout the United States and Canada.

Osage orange has an adult height of 30-50ft and is often wider than it is tall.  The leaves are 3-5 inches long and 2-3 inches wide, with an oval shape that ends in a slender point.  The leaves are alternately arranged on the thorny branch. They are a dark shiny green on top and paler on bottom, turning yellow in the fall.  The tree has a characteristic arching branch pattern and noticeably colorful bark which aid in identification.

This tree is known for its unusual fruit, which some producers are growing for bioproducts. The fruit looks like a thick orange but is yellow/green on the outside and has more pronounced bumps than an orange.  The fruit produces a milky fluid and woody pulp.  Even though the fruit resembles an orange it is more related to the mulberry family. Although it is not poisonous, the fruit is not usually eaten by animals or humans because of its hard-dry texture. Still, squirrels sometimes eat the seeds as food.  Osage orange is a dioecious species, which means only female trees will produce fruit.

Bois D’arc are hardy to most of the United States and can grow in many different environments but prefer fertile, deep soil.  They can be used for hedge rows as a natural barrier to cattle, the wood is a strong and dense which makes it great for fence posts, tool handles, treenails, and even bows (hence the name given by French explorers).  The yellow-orange color of the wood makes it attractive for many different uses. Osage orange typically lives about 75 years with a moderate growth rate of about 1 foot per year.

In the Cross Timbers, there are several large specimen trees. Vandergriff Park in Arlington has several large Osage orange along Johnson Creek, such as the tree pictured at the top of the page and shown on this map:

Unique Trees of North Texas:

Pecan

(Carya illinoinensis)

By Laura M. Miller

The pecan is an overachieving member of the Juglandaceae (Walnut) family and a large growing, long lived, nut producing tree native to North Texas. A mature tree can be over 100 feet tall and 100 feet wide with a lifespan of over 300 years. The native range of the pecan stretches from Northern Mexico to Northern Illinois where pecans can be found along the banks of the Mississippi river almost all the way to Dubuque, Iowa.

Pecans are one of the easiest deciduous trees to identify in the winter because the shucks that protect the developing nuts usually remain attached to the stems.  The presence of nuts on the ground is also an excellent indication that a pecan tree is nearby.  Pecans produce alternately attached large pinnately compound leaves with 9-17 leaflets.  In spring, they are one of the last trees to leaf out.   Separate male (catkins) and female flowers are produced soon after bud break. The female flowers are borne in clusters on the tips of branches.  The year of a heavy pecan crop, one where nut clusters develop on 50% or more of the branch terminals, are usually followed by a year of light production.  Pecan leaves turn yellow before falling from the tree around the time of our first frost.  Falling leaves are soon followed by falling nuts. Because they smell and look a lot alike, pecan trees can be confused with Black Walnut, Juglans nigra, or any of the nine species of hickory that are native to Texas.  They are sometimes mistaken for other commonly planted species with similar pinnately compound leaves such as Chinese Pistache, Pistacia chinensis, or the native Western Soapberry, Sapindus saponaria, both producers of inedible berries rather than delicious nuts.

Long before being named the State Tree of Texas in 1919, the pecan played an important role in Texas history.  When Cabeza de Vaca was shipwrecked in Texas in 1528, he documented the pecan as an important dietary staple of the Native Americans he encountered.  Pecans were gathered in the fall and eaten through the winter months when food was scarce. Today residents of North Texas can gather or purchase pecans and keep them in the freezer for those times when food is scarce.  A one ounce serving of pecans provides 3g dietary fiber (11% Daily Value), 3g plant protein, mostly monounsaturated fat and significant quantities of Thiamin, Beta carotene, Magnesium, Manganese, Copper, and Zinc.

Native pecan trees are found primarily in deep alluvial soils near rivers and streams and are especially abundant along the major rivers of North Texas, the Red, Trinity, and Brazos.  Pecans can be planted at any site in North Texas that can accommodate a large shade tree.

Native pecan trees produce nuts that vary in size, shell to nut ratio, and flavor, Since the 1880s, which is not very long for a cultivated crop, horticulturist have been selecting the best native trees for propagation.  In the 1930s, the United States Department of Agriculture began a pecan breeding program that continues to this day in Brownwood and College Station.  Many of the most highly recommended cultivars for the Cross Timbers have come from this program including Caddo, Oconee, Pawnee, Kanza, Nacono, Sioux and Wichita.  Desirable, the leading cultivar in the state that produces the most pecans whose name must not be mentioned, is also an excellent choice.  The sentimental favorite is probably Burkett, a native selection widely distributed by J.H. Burkett North Central Texas in the 20s and 30s. The trees of cultivars made famous by Arlington nurseryman O.S.Gray in the 40s, 50s, 60s, and 70s such as GraKing and GraTex still grow in many Arlington landscapes.

Even though no other shade tree offers the key ingredient to delicious pies, pralines, cookies, and German Chocolate Cake frosting, pecans do have some negative qualities as landscape trees.  They are messy dropping not just nuts in the fall but also leaves and petioles that don’t rake up easily.  In the spring those male flowers can be almost as much trouble to clean up as the leaves in the fall.  Couple this with a tendency to drop branches due to shade, heavy nut crops and possibly just because they want to, and you have a tree that is exceptionally well suited to someone who very much enjoys picking up sticks (and leaves, and petioles, and catkins).  Like most plants that produce something good to eat, pecan trees will attract lots of birds, especially crows, squirrels, racoons, and foraging neighbors.  Insects are also fond of pecans, and you can expect Pecan Nut Casebearers, Hickory Shuckworms, and Fall webworms. Pecan scab is a serious fungal disease problem east of I-35 and can be problematic here if environmental conditions are conducive to disease development.  Fortunately, there are many excellent cultivars that are scab resistant.  Pecans grown on high pH calcareous soils benefit from foliar zinc sprays.

The National Champion pecan (pictured above) is in Parker County near Weatherford. In the Palo Pinto town of Oran, the Goodnight-Loving Pecan sheltered the 1866 partnership of cattlemen Charles Goodnight and Oliver Loving. In Fort Worth, the Hollow Pecan of the Fort Worth Botanic Garden (RIP 2014) no longer shelters small children hiding from their parents, but there are many old large native pecan trees there and across University Avenue in Trinity Park.