An Abundance of Acorns

Texas Red Oak displaying fall color.

Texas is famous for its oak trees, with over 50 different species found in the Lone Star State.  Each of these oak species produce acorns, also called oaknuts or mast, which is a collective term for fruits or nuts.  The word acorn is related to Gothic term akran which has been interpreted to mean ‘the fruit of the unenclosed land.’  When oaks are dominant in the landscape, as they are here in central Texas, they play an important role in the ecology of the forest.

Acorns usually contain one seed enclosed in a tough, leathery shell, and have a cup-shaped cap or cupule. Depending on the oak species, acorns can take from 5 to 24 months to mature.  As a general rule, acorns mature in late summer, turning green to brown, and start falling from oak trees in September and October.  Acorns produced by trees in the red oak family (such as Texas Red Oak, Quercus buckleyi) take two years to mature, while acorns produced by trees in the white oak family (such as Bur Oak, Quercus macrocarpa) only take one year. 

Texas Red Oak Acorns

Some years, known as mast years, trees produce copious amounts of acorns with smaller crops in the years between.  Scientists have proposed a range of explanations for the mystery of what might trigger a mast year, but they do know that it is not resource-driven as annual rainfall and temperature fluctuations are generally much smaller in magnitude than the variation in the crop sizes of acorns.  Some scientists hypothesize that masting trees are trying to maximize pollination efficiency.  If these trees flower and release pollen at the same time in order to increase their chances of reproduction, since large amounts of pollen correlate with larger amounts of germination, they ultimately produce more acorns.  Large, occasional outputs of seeds like acorns appears to be more favorable than frequent, smaller outputs.

Bur Oak acorns are our largest acorns.

Boom and bust years of acorn production actually benefit oak trees from an evolutionary perspective, because acorns are an important, highly nutritious food source for many animals including squirrels, mice, turkeys, blue jays, pigeons, ducks, deer, and bears.  In a mast year, these animals can’t consume all of the acorns produced, so some are left to germinate and grow into future oak trees.  In leaner years, animal populations are kept in check so there are fewer animals to eat the acorns in the mast years.  Over time, a higher proportion of acorns survive to become oak trees.

Copious amounts of acorns are produced in a mast year.

Too heavy for wind dispersal, acorns need other ways to spread beyond the mother tree into a suitable area for germination.  Jays, squirrels, and some woodpeckers serve as the main dispersal agents, as they gather and hoard acorns in caches.  While they are remarkable in creating mental maps of their cache locations, these animals rarely eat every single acorn, so a small number manage to germinate and produce the next generation of oaks.

The Blue Jay is one of many species that cache acorns.

As autumn arrives and acorns mature and fall from our oak trees, think of the potential in the abundance of acorns produced.  As Henry David Thoreau once wrote, “Every oak tree started out as a couple of nuts who stood their ground.”  

Beat the Heat

 

Flame Acanthus is a hot weather bloomer.

The heat of the Texas summer is enough to make everything wilt, but there are some native plant species that truly thrive in these unrelenting temperatures and drought-stricken conditions.  These plants include Turk’s Cap (Malvaviscus arboreus var. drummondii), Flame Acanthus (Anisacanthus quadrifidus var. wrightii), Violet Ruellia (Ruellia nudiflora), and Western Ironweed (Vernonia baldwinii).

Turk’s Cap, also known as Drummond’s Turk’s Cap, Wax Mallow, Mexican Apple, Manzanita, and Sleeping Hibiscus, is a spreading shrub to 4 feet high, with large green leaves on upright stems.  Bright red flowers atop the stems are twisted into a whorl from which protrude red stamens.  These flowers are a natural source of nectar for hummingbirds and butterflies, and it is a host plant for the Turk’s-cap White-Skipper butterfly.  The resulting fruit is red and marble-sized, and edible for animals and humans alike. Turk’s Cap is the perfect plant to grow under trees that tend to shade out non-native turf grasses, as they form a natural cover and provide much needed color from May all the way to November.

Turk's Cap

Turk's Cap fruit

Turk's-cap White-Skipper

An airy, spreading shrub to 5 feet tall, Flame Acanthus has tender lance-shaped green leaves and tubular red flowers that open to 4 lobes and occur along terminal spikes.  Blooming in full sun from June to October, it attracts both hummingbirds and butterflies, and is also known as Hummingbird Bush, Wright’s Acanthus, and Mexican Flame.  It is the host plant for the Crimson Patch, Elada Checkerspot, and Texan Crescent butterflies. The fruit is a small, hood-shaped capsule with seeds attached to a hooked stalk that helps to eject them from the capsule when it dries and splits open.

Flame Acanthus

Flame Acanthus seed capsule

Crimson Patch

Violet Ruellia is an erect herb that is woody at the base with few branches, growing to 2 feet tall.  The dark green leaves are oval-shaped, and the trumpet-shaped violet flowers at the ends of stalks open at sunrise and fall from the plant in early afternoon, from March all the way through October. Also called Wild Petunia, it does well in sunny areas and is a host plant for the Common Buckeye butterfly.  One of its’ subspecies is a host plant for the Malachite butterfly, a south Texas species rarely seen in central Texas.

Violet Ruellia

Common Buckeye

Often stout and forming colonies 5 feet high, Western Ironweed has hairy unbranched stems, large green leaves with serrated edges, and loose clusters of bright purple blooms at the apex of each stem.  From July to the first frost, these fuzzy blooms provide nectar for various types of pollinating insects and the seeds nourish several species of birds.  Also called Baldwin’s Ironweed, it is the host plant for the Parthenice Tiger Moth.  While this species’ growth can be aggressive, it flourishes if allowed to spread in larger, open, sunny areas.

Western Ironweed

These native species can (and often should) be pruned back in winter as they can get too leggy.  They have low water needs once established, and can tolerate hot temperatures and still continue to bloom.  They are the perfect plants to beat the heat, benefit our local wildlife, and provide much needed color in your own native summer garden!

Undervalued Vines

  The uncommon Plateau Milkvine is often mistaken
for the more common Pearl Milkvine (above).

Every species of native plant has its purpose, and while many are valued by humans for their fragrant flowers and foliage, those that are valued for their role in keeping the earth’s nutrient cycles intact should be regarded as having the highest value.  Those nutrient cycles need to be protected through plant preservation or restoration, as they are what provides nourishment for the lifecycles of our native wildlife and protects the health of our ecosystems.

Even among those folks who are familiar with many native plants that perform this role, there are some little-known species that are often overlooked and under appreciated.  In Central Texas, there are a few species of vines in the Milkweed family that many fail to notice, including Star Milkvine (Matelea biflora), Plateau Milkvine (Matelea edwardsensis), and Bearded Swallow-wort (Cynanchum barbigerum).  

Star Milkvine, also called Purple Milkweed Vine, is a relatively common vine that grows in pastures, prairies, and other open ground, usually in chalky soil throughout Central and North Texas.  This small, trailing vine to 2 feet has five-petaled, star-shaped, deep purplish-brown flowers that are 0.5 inches wide.  Blooming from March to June, the flowers occur in pairs along the trailing stems that radiate from a central rootstock, and arise from the axils of the opposite, triangular leaves.  The flowers, leaves, and stems are all quite hairy, as is true of many members of the Milkweed family.  Its habit is to grow low among grasses, often in areas that are mowed, so it is frequently passed over by humans, but is a useful host plant for Queen and Soldier butterflies and a nectar plant for several species of bees.

Star Milkvine has low-growing stems that radiate out
from a central rootstock.

The unusual flowers of Star Milkvine occur in pairs.

Soldier

Sometimes mistaken for the more common Pearl Milkvine, Plateau Milkvine is a vine to 3 feet that is endemic only to the Edwards Plateau of Central Texas.  This uncommon vine shares the same twining habit of Pearl Milkvine, but its leaves, while similar, generally have a somewhat wavy edge, and its flowers are bell-shaped instead of flat. Additionally, its 0.7 inch wide greenish-white flowers do not have a pearl center, and its petals are not solely reticulate-patterned, having parallel veins in their lower halves and centers, and reticulate or networked veins only on the edges or margins.  Blooming in April and May, this vine can be found on gravelly soils in open woodlands, often climbing on other plants, and is a native host plant for Queen butterflies.  Due to indiscriminate land clearing, this plant is listed as ‘vulnerable’ in terms of its conservation status in Texas.

Plateau Milkvine is a rare cousin to Pearl Milkvine.

The flowers of Plateau Milkvine distinguish it
from Pearl Milkvine.

Queen

Growing up to 8 feet long, Bearded Swallow-wort, also called Thicket Threadvine and Aphid Vine, is a delicate vine that climbs on shrubs and small trees in open woodlands, in thickets, and along roadsides and fencerows in the Edwards Plateau and South Texas. It has small glossy lance-shaped, opposite leaves to 2 inches long, and from March to August, tiny creamy-white flowers appear in loose clusters from the leaf axils.  These flowers are 0.25 inches wide, bell-shaped, and have five distinctively hairy or ‘bearded’ recurved petals.  Five similar species in this genus are present in Texas, but this is the only one with ‘bearded’ flower petals.  Aphids are often found on this plant, giving rise to one of its other common names, and it is the host plant for the Obscure Sphinx Moth (Erinnyis obscura).

Bearded Swallow-wort is a rather delicate climbing vine.

The fringed or 'bearded' flowers
of Bearded Swallow-wort.

Obscure Sphinx

Whether it is due to their scarcity or diminutive stature, it is easy to miss these vines.  While they might be undervalued by humans, they are quite valuable to our native wildlife!

Introduced Invaders

 

Closeup of a Bastard Cabbage bloom

Spring brings new growth to all types of plants, including those species known as non-native invasives.  Non-native plants, also called exotics, are defined as plants ‘growing in a place that is not the region where they naturally grow’, and invasive plants are defined as plants that are ‘both non-native and able to establish on many sites by growing quickly and spreading to the point of disrupting native a plant community or ecosystem’.  

While plants that are non-native or invasive can be problematic, when a plant is both non-native and invasive, it can quickly outcompete native plants.  These invaders can produce copious amounts of seed easily transmitted by wind, water, or birds, thrive on poor or disturbed soils through aggressive root systems, have an early growth season or produce growth-inhibiting chemicals, and ultimately disrupt natural nutrient cycles of wildlife.  

In Central Texas, the species that cause the most harm to the local environment include Ligustrum (Ligustrum sp.), Nandina (Nadina domestica), Chinaberry (Melia azedarach), Chinese Tallow (Triadica sebifera), Bastard Cabbage (Rapistrum rugosum), and Japanese Honeysuckle (Lonicera japonica).  Most of these species have been introduced to the United States via the nursery trade as ornamentals, and unfortunately many are still sold today.

Ligustrum or Glossy Privet

Ligustrum or Glossy Privet, native to China, Japan, and Korea, is an invader of roadsides, thickets, open woodlands, and disturbed areas.  This evergreen tree to 40 feet has simple green, glossy pointed leaves.  It is widely cultivated and frequently escapes to invade and dominate the woodland understory, as its abundant purple-blue fruits are easily spread by birds and other animals.

Nandina or Heavenly Bamboo

Nandina or Heavenly Bamboo, native to China and Japan, is an invader of landscapes, roadsides, and other cultivated areas.  This erect, multi-stemmed shrub to 8 feet has compound green leaves to 12 inches long that are tinged with red in winter.  It spreads by escaping cultivation through underground root sprouts and animal-dispersed seeds, and quickly forms a colony.  Additionally, its shiny red fruits are toxic to small children, pets, and some grazing animals.

Chinaberry

Chinaberry, native to parts of Asia, is an invader of roadsides, thickets, open woodlands, and disturbed areas.  This deciduous tree grows up to 50 feet and has compound green leaves to 24 inches long.  Lavender blooms distinguish it from the similar but native Western Soapberry (Sapindus drummondii), which has white blooms.  It spreads on site via fast-growing root sprouts and over longer distances via bird-dispersed seeds from its golden-yellow fruits.

Chinese Tallow

Chinese Tallow, native to China and Japan, is an invader of cultivated landscapes and other moist areas.  A deciduous tree that grows to 60 feet, it has diamond-shaped leaves with elongated tips that turn orange-red in fall.  It reaches reproductive age in as little as three years, producing prolific amounts of seed that is readily transported by birds and water.  It is difficult to eradicate once established, and can effectively transform a native habitat into a monoculture.

Bastard Cabbage

Bastard Cabbage, also called Common Giant Mustard and Turnipweed, and native to southern Europe, northern Africa, and western Asia, is an invader of meadows, fields, roadsides, and other disturbed areas.  This many-branched herb grows to 5 feet, with clustered of small lemon-colored flowers at the tips of branches.  Its seeds germinate early in spring, quickly covering the ground with a dense blanket of leafy rosettes that block sunlight from reaching seedlings of native plants.  It reseeds rapidly and forms large monocultures.

Japanese Honeysuckle

Japanese Honeysuckle, native to Japan, is an invader of thickets on disturbed floodplains, creeks, and river banks.  This climbing, sprawling vine grows to 80 feet, with simple oval leaves and tubular white flowers that turn butter-yellow as they age.  Choking out other species by girdling or by blocking out sunlight through overgrowth, its plentiful seeds are easily dispersed by birds and other wildlife.  It is not to be confused with the native, much less aggressive White Bush Honeysuckle (L. albiflora). 

Replacing these non-native invasive plants with native plants help restore natural habitat, preserve and produce much-needed soil, protect fragile waterways from erosion, and as a result, keep vital nutrient cycles intact for all forms of wildlife.  Natives are already adapted to our soils and climate so they require little to get established, are naturally hardy and disease-free, and they provide food, shelter, and places to raise young for local insects (especially pollinators), birds, and other wildlife.  Natives are also a beautiful reminder of the unique natural heritage of Texas, so please consider to replacing your non-native invasive plants with natives today.  Once established, you’ll be amazed at how they bring your landscape to life!

INVADER                                NATIVE REPLACEMENT(S) - some ideas...

Ligustrum species                    Escarpment Black Cherry, Mexican Plum

Nandina                                    Yaupon, Possumhaw, Rusty Blackhaw Viburnum, Sumacs

Chinaberry                                Western Soapberry, Oaks, Redbud, Mexican Buckeye

Chinese Tallow                          American Sycamore, Black Willow, Texas Ash

Bastard Cabbage                      Mistflowers, Salvias, Sages

Japanese Honeysuckle            White Bush Honeysuckle, Coral Honeysuckle

Beguiling Bloomers

Pink Stonecrop

Springtime in Central Texas brings a host of familiar wildflowers blooming in meadows and woodlands, and along grassy roadsides. But each year the seasonal conditions may vary, based largely on the timing and amount of rainfall.  While many species are widespread from year to year, some appear infrequently, others only in certain habitats, and many go almost completely unnoticed.

Clasping Venus’ Looking-glass

Clasping Venus’ Looking-glass or Clasping Bellflower (Triodanis perfoliata) is a distinctive annual that can be found growing in open often disturbed areas, sometimes appearing even in cultivated flower gardens.  In April and May, violet-blue, 5 petaled, wheel- to bell-shaped flowers, 0.5 to 0.75 inches across, are set singly in the axils of rounded green leaves that clasp the erect, slender, unbranched stems.  Inconspicuous at 6 to 18 inches high, this species is differentiated from five other Triodanis species found in Texas by its almost circular, toothed, clasping leaves.

Pink Stonecrop, also called Widow's Cross

Pink Stonecrop or Limestone Stonecrop (Sedum pulchellum), is a low-growing, apparently rare annual found on rocky ground in full sun, often among cactus and other Sedum species. Smooth, stem-clasping, cylindrical pale to lime green leaves (often with a reddish tinge), to 1 inch long, are densely arranged along the ascending to spreading stems.  These stems are topped with horizontally branched inflorescences that bloom from March to May, with numerous 4-petaled, pale pink flowers, to 0.5 inches across.  The petals are arranged in a cross-like pattern, giving rise to its other common name of Widow’s Cross. The Travis County population of this species, most often found on hilltops in the Bull Creek watershed, is disjunct by over 150 miles from other more eastern and northern populations, and likely represents the southwestern limit of its native distribution.

Heller's Plantain

Highly overlooked but quite common is Heller’s Plantain or Cedar Plantain (Plantago helleri), an erect annual that grows only in Central to West Texas and in southern New Mexico, typically in shallow, stony soils and on limestone bedrock exposures. From March through May, this species displays unusual, slightly overlapping flowers clustered at the top part of each stalk.  The flowers are quite small at 0.25-inches wide, with 4 off-white, nearly translucent petals that have a dark red center.  The stalks, to 10-inches high, arise from narrow, linear, basal leaves, to 8-inches long, and both stalks and leaves are softly hairy.  This species is can be commonly found along gravelly roadsides, and it is one of the host plants for the beautiful Common Buckeye butterfly.

Common Buckeye

Each spring, remember to look beyond the bluebonnets, paintbrushes, firewheels, and Mexican hats and take a closer look, because you just might be rewarded with one of these beguiling little bloomers!

Resilient Trees

The beginnings of Winter Storm Uri

With winter storm Uri well behind us, many observations are being made regarding which tree species successfully survived the 8-day stretch of extreme winter weather conditions.  First and foremost, all trees that are native to Central Texas generally fared much better than their non-native counterparts.  Over the centuries, native species have adapted to all sorts of weather conditions, from cycles of droughts and floods, heat and cold, and even accumulations of ice or snow.  These adaptations greatly increase each native species’ resiliency over time.

A second factor that determined the survival of a native tree species was whether it was evergreen or deciduous.  The foliage of evergreen species increases the surface area that can trap ice and heavy snow, causing limbs to bow, split, and break, which can weaken the entire structure of the tree.  While deciduous trees can be covered in ice and snow, in winter they do not have foliage that can trap the extra weight that can cause permanent damage.

Third, established plants have a much better chance of survival in extreme winter weather conditions, so now is the time to plant!   While there are many desirable native trees that are deciduous, there are several that are also attractive bloomers in the spring, including Escarpment Black Cherry (Prunus serotina var. eximia), Roughleaf Dogwood (Cornus drummondii), and Rusty Blackhaw Viburnum (Viburnum rufidulum).

Escarpment Black Cherry in bloom

Escarpment Black Cherry fruit

Found only in the limestone-based soils in Central Texas, Escarpment Black Cherry is a distinct and isolated subspecies of native Black Cherry (Prunus serotina). Growing up to 50 feet tall, it is distinguished from other subspecies in Texas by its intermediate height and its virtually hairless, pointed elliptical green leaves with finely toothed margins that turn golden yellow in fall. It has attractive silvery bark and long showy clusters of tiny white flowers in March to April followed by purplish-red fruits that are favored by wildlife.  This native cherry prefers sunny areas in wooded canyons and on slopes, and is a larval host plant for many species of butterflies and moths including Eastern Tiger Swallowtail, Two-tailed Swallowtail, Cecropia Moth, and White Furcula.

Roughleaf Dogwood in bloom

Roughleaf Dogwood fruit

Roughleaf Dogwood is a small tree to 16 feet with opposite, prominently veined, oval, green leaves with an abruptly drawn-out tip, slightly rough above and slightly velvety below, that turn purplish-red in fall.  From April to early June numerous broad clusters of cream-colored flowers appear at the ends of branches, developing into small, fleshy, bright white, spherical fruits.  This native dogwood prefers partially shady, wooded limestone hills, and provides cover for various species of wildlife, especially birds, as it spreads from root sprouts and if allowed, eventually creates a natural thicket.

Rusty Blackhaw Viburnum in bloom

A shapely small tree, typically to 18 feet but sometimes taller, Rusty Blackhaw Viburnum has attractive, glossy dark-green paired leaves that turn reddish-purple in fall, reddish-brown twigs, and dark bark that separates into rectangular plates. Platter-shaped clusters of tiny, creamy white flowers in March to April are followed by small, oval, waxy, blue-black fruits that are relished by several species of birds and mammals.  This native viburnum prefers woodland edges and thickets in partial shade, and is of special value to native pollinators like bumble bees.

Rusty Blackhaw Viburnum fruit

Rusty Blackhaw Viburnum fall color

It’s important to note that while winter storm Uri was no doubt an exceptional weather event, it’s never too early to plant some of our more resilient native trees!

Frost Flowers

Blooming from August to November, Frostweed provides late season nectar
and a unique surprise at the first frost.

Accompanying the crunching of fallen leaves and the rattling of seed pods drying in the breeze is the arrival of the first frost.  This marks the seasonal change from our relatively warm autumn to the cooler days of a mild central Texas winter.  How does frost, this sparkling layer that sometimes covers the fall landscape, form? 

When the temperature of the air reaches a point where the water vapor in it can condense out into water, it is called the dew point.  The frost point is when the dew point falls below freezing, and rather than producing dew, it creates frost.  Consisting of tiny, spike-like crystal structures called spicules that grow out from a solid surface, frost generally forms on surfaces that are colder than the surrounding air.  Even the size of the crystals can vary, depending upon the amount of time they took to grow, the relative changes in temperature, and the amount of water vapor available. 

A frost flower.

Cold air is denser than warm air, so quite often lower areas become colder on calm nights due to differences in elevation.  Known as surface temperature inversion, this phenomenon forms ‘frost pockets’ or areas where frost forms first, due to cold air trapped against the ground.  It is here, in these areas, that you can find a rare and wonderful spectacle of nature called ‘frost flowers.’

While many plants can be damaged or killed by freezing temperatures or frost, this varies by the type of plant and tissue exposed to these conditions.  In central Texas, there is a common plant called Frostweed (Verbesina virginica), which is found in low-lying areas near streams, creeks, canyon bottoms, and in dappled shade at woodland edges. 

Bordered Patch

Silvery Checkerspot

Much of the year, Frostweed goes unnoticed while it grows 5 to 8 feet tall and leafy, the top of each stalk crowned by a cluster of small white flowers.  Its stalks are oddly square-like, with fleshy green flanges. Frostweed begins to bloom in the August heat, and continues until first frost, well into the fall.  These flowers provide late-season nectar for many insects, including bees, beetles, flies, wasps, and even migrating hummingbirds and Monarch butterflies.  It is also a host plant for Silvery Checkerspot and Bordered Patch butterflies.

A patch of frost flowers.

With the first frost, however, the water contained in each Frostweed plant stem expands, causing the stems to crack.  Via capillary action, more water is drawn through the cracks, freezes when it hits the cold air, and forms long curls of ice like petals of a flower, ribbons, or other delicate, abstract sculptures.  Most often, they consist of longitudinal bands of fine ice threads at right angles to the stem.  These delicate flowers of the frost are fleeting in nature, and can only be found in early morning, as the rising temperature quickly melts them away. 

A prime example of crystallofolia.

Only a few species of plants exhibit this unique phenomenon, which has been called ‘crystallofolia’ by Bob Harmes at the University of Texas, from the Latin crystallus or ‘ice’ and folium or ‘leaf’.  Much is left to be discovered reading the purpose of this process, but further research by Dr. James Carter at Illinois State University has concluded that the ice formation often far exceeds the amount of moisture locally available within the plant’s stem, so it must be augmented by water drawn up from the roots.

Delicate curls can form when more plant moisture is available.

On the surface, fall may seem as if nature is shutting down for the winter, but take the time for a second look and you just might be surprised.  The first frost of the season is another intriguing part of the ongoing cycle of life and renewal for our native plants and animals.