Poisonous or Venomous?

Poison Ivy

Often used interchangeably when describing some plants and animals, in reality poisonous and venomous mean two different things.  Poisonous describes plants or animals that are harmful when consumed or touched.  Venomous refers to animals that inject venom into their prey, by means of a bite or sting, when hunting or for self-defense.  To add to the confusion, all venoms are a poison but not all poisons are venoms!

Poisonous species typically produce a toxin that can range from irritant to fatal. Plants such as Poison Ivy (Toxicodendron radicans) and some members of the Spurge family are considered irritants when they come in contact with skin, but this effect is produced through different mechanisms.  Nearly all parts of the Poison Ivy plant contain urushiol, which is a substance that gives us contact dermatitis, or a severely itchy and painful inflammation of the skin.  

Texas Bull Nettle

Spurges such as Texas Bull Nettle (Cnidoscolus texanus) and Betonyleaf Noseburn (Tragia betonicifolia) have raised structures called trichomes that are capable of ’stinging' animals and humans that brush against them.  These plants have trichomes on their leaves and stems that have bulbous tips that break off and reveal needle-like tubes that pierce the skin. They can cause an itching, burning rash by emitting onto the skin a mix of acetylcholine, formic acid, histamine, and serotonin.  

Jimsonweed or Sacred Datura

One local native plant, Jimsonweed or Sacred Datura (Datura wrightii) goes well beyond irritant to hallucinogenic and even fatal if ingested.  All parts of this plant contain toxic alkaloids, and the narcotic properties of this plant have been known by humans since before recorded history.  They once figured prominently in important religious ceremonies of various southwestern Native American tribes.

Gulf Coast Toad

Animals that are poisonous include most amphibians (frogs, toads, salamanders, and newts), that have some amount of toxins on their skin and within other tissues. Special skin glands produce useful proteins, some for use in respiration, others for fighting bacterial or fungal infections, and at least one in each species that is used for defense.  For example, many toad species will release their toxins when they feel threatened, such as when they are caught by a dog or cat, and can trigger drooling, vomiting, and respiratory or cardiac problems.

Western Diamondback Rattlesnake

While some snakes are the most commonly known venomous animals, all spiders, some lizards, and many bees, ants and wasps are venomous as well.  The venoms they inject through a bite or sting contain various classes of toxins designed to perform specific biological effects such necrosis or death in multiple cells (necrotoxins) or individual cells (cytotoxins), disruption of the nervous system (neurotoxins), or damage to muscle tissue (myotoxins).   The venom of our Western Diamondback Rattlesnake (Crotalus atrox) carries both necrotoxins and myotoxins, Black Widow spiders (Latrodectus macrons) carry both neurotoxins and cytotoxins, and Striped Bark Scorpions (Centruroides vittatus) and Texas Redheaded Centipedes (Scolopendra heros) carry neurotoxins.

Striped Bark Scorpion

Texas Redheaded Centipede

While the vast majority of snake toxins are transferred by bite, one exception includes garter snakes (Thamnophis sp.), which are small and harmless in terms of their bite but are toxic to eat because their bodies absorb and store the toxins of their amphibious prey.  In our area, these snakes include the Black-necked Garter Snake (T. cyrtopsis) and the Western Ribbon Snake (T. proximus).

Western Ribbon Snake

It is important to keep in mind that many plants and animals that are poisonous or venomous are not necessarily a guaranteed threat to humans, as much depends on how the plant or animal is encountered, its toxicity level, and the amount of toxin absorbed.  Regardless, respecting these species and giving them their space is the cardinal rule.  Interestingly, the medicinal use of venoms for therapeutic benefit in treating diseases dates back to 380 B.C. in ancient Greece.  Today, the venoms produced by different organisms, which contain hundreds of different bioactive elements, are isolated, purified, and screened, then studied to identify components that may have desirable therapeutic properties.  This research is often the starting point for developing a therapeutic drug, and those types of drugs on the market today are used to lower high blood pressure, relieve severe pain, act as blood thinners, treat Type 2 diabetes, and stop bleeding during surgical procedures.

Distinctly Different Milkweeds

Pearl Milkvine

Much ado has been made of the more common and widespread milkweed species, but there are a handful of milkweed vines that are less common but more distinct, and just as useful as native host plants for Monarchs and related butterflies.

A fairly robust, twining vine 6 to 12 feet long growing in dry, light shade in thickets on rocky hillsides and woodland edges, Pearl Milkvine (Matelea reticulata) is best known for its heart-shaped leaves and flat, greenish-white flowers ½ to ¾ of an inch across with pearly, iridescent centers.   Also called Green Milkweed Vine, Net Vine Milkvine, and Netted Milkvine, its curious flowers have tiny white veins forming an intricate pattern on the surface of the petals, adding to their unusual look. In fact, ‘reticulata’ refers to this pattern, which mans ‘resembling a net or network’.  It blooms from April to July, especially in full sun, giving way to fairly large, interesting prickly follicles filled with seeds attached to silky threads.  This native species is a host plant to Monarch butterflies.

Plateau Milkvine

Both the Pearl Milkvine and Plateau Milkvine have prickly seed follicles

Often mistaken for Pearl Milkvine is Plateau Milkvine (Matelea edwardensis), 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 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 species can be found on gravelly soils in open woodlands, often climbing on other plants, and it is a native host plant for Queen butterflies.

Pearl Milkvine Flowers

Plateau Milkvine Flowers

Purple Milkvine

Usually found in the chalky soils of pastures and open ground, Purple Milkvine (Matelea biflora) has low-growing stems that radiate along the ground from a woody rootstock, and along with its opposite, triangular leaves, are covered with long, spreading hairs.  From March to June, pairs of star-shaped, five-petaled, dark purple-brown flowers rise from the base of the leaves, which gives this plant its other common name of Star Milkvine.  While its trailing stems can grow up to 2 feet long, it inhabits grassy areas and as such is often hidden and overlooked, except by Queen and Soldier butterflies who use it as their native host plant.

Talayote

Named for a small town in Chihuahua, Mexico, Talayote (Cynanchum racemosum) or Milkweed Vine is a climber that grows to 15 to 20 feet in full sun to part shade, and is a native host plant for both Queen and Soldier butterflies.  Talayote produces clusters of small cream and green flowers that are held above and among the heart-shaped leaves, blooming in the hotter months from summer into fall, and attracting a host of other small but beneficial pollinators.  Growing only in Central, South, and West Texas in the United States, this vine produces plump, smooth follicles 3 inches long, filled with silk-topped seeds, often remaining on the vine well into winter. 

Take the time to seek out and appreciate these lesser known members of the Milkweed family, as they are beautifully and distinctly different!

A Horse of a Different Color

Horsetail or Scouring Rush

Few plant species that grow naturally today have been around for over 100 million years, but one of the best known are plants in the genus Equisetum, which is the only living genus of the entire family of Equisetopsida, most commonly known as horsetails.  They are recognized as close relatives of ferns, typically growing in wetter areas with whorls of needle-like branches radiating at regular intervals from each single vertical stem.

The common name of horsetail is used for the entire group of plants, since the branched species resemble a horse’s tail.  In fact, the genus Equisetum comes from the Latin equus or ‘horse’ and seta or ‘bristle.’  Another common name is scouring rush, referring to the upright rush-like appearance of the plants, and the fact that the longitudinal ridges of the stems are coated with abrasive silicates, making them useful for scouring or cleaning metal items.  It is still used today as a traditional polishing material in Japan.

The primary species of horsetail that occurs natively in wet or moist areas of Texas, most commonly on the Edwards Plateau and in Blackland Prairie, as well as most of the non-tropical northern hemisphere, is Equisetum hyemale.  A spreading, reed-like perennial growing to 3 feet tall, each stem is evergreen, cylindrical, jointed, hollow, and about 1/4 of an inch in diameter.  In this species, the needle-like branches appear non-existent, but are actually small and fused around the stem at each joint or node, forming a blackish-green band or sheath.  Interestingly, the pattern of spacing of the nodes in these plants, which grow increasingly close together toward the apex, is precisely what inspired Scottish mathematician John Napier to discover logarithms in the late 16th century.

Dragonflies, like this Neon Skimmer, love to perch on the cones of
the horsetail’s upright stems.

Horsetail prefers open or wooded areas along streams, moist flats, and wet ledges. Like ferns and other related species, horsetails reproduce by spores rather than through seed-producing flowers. These spores are borne in cone-like structures at the tips of some stems, and are mostly homosporus, meaning of the same size and type.  The tiny spores have four elaters or structures that alter shape in response to changes in moisture, effectively acting as moisture-sensitive springs that assist spore dispersal through crawling and hopping motions once released from the cone.

Horsetails reproduce by spores borne in the cone-
like structures at the tips of some stems.

The upright, evergreen, segmented foliage of horsetail is an appropriate plant for a rain garden, pond edge, water feature, or area with moist soil, and is an excellent perching plant for dragonflies. While it can spread quickly by underground or underwater runners, it is easily kept in check by periodic pulling or by planting it in a container.  Few plants add as much interest or vertical structure to a wildscape as this living fossil, which is clearly a  ‘horse of a different color’!

Marvelous Mahonias

Agarita showing its simple trifoliate leaflets.

One of the constant debates in the botany world is whether or not the genus Mahonia should stand alone or be included in the genus Berberis.  This discussion is based on the fact that several species in both genera are able to hybridize, and when viewed as a whole, no consistent separation exists except for simple versus compound leaves.  Taxonomy debate aside, the two most marvelous Mahonias in Texas are the well-known Agarita (Mahonia trifoliata) and the lesser-known Texas Barberry (Mahonia swaseyi).

Agarita with red berries.

Also called Agarito, Algerita, Laredo Mahonia, Laredo Oregon-grape, Trifoliate Barberry, and Texas Wild Currant, Agarita is a 3 to 8 foot evergreen, thicket-forming shrub with gray-green to blue-gray simple leaves composed of 3 leaflets.  Holly-like, each lobe of the leaflets ends in a sharp spine, and the woody stems are bright yellow inside.  Small yellow flowers appear in February and March, followed by red, berry-like fruits from May to July. Agarita grows throughout most of South-Central and West Texas, and prefers hills, rocky slopes, and open woods that have well-drained but rocky, limestone soils.  Songbirds and small mammals will eat the fruits, and use the prickly plant for cover.  In West Texas Agarita is used as a larval host plant for the Chinati Sheepmoth, one of our native wild silk moths.

’Texas Barberry has a more compound leaf structure.

Texas Barberry, also known as Texas Oregon-grape, is a 3 to 5 foot evergreen shrub with 3 inch long compound leaves composed of 2 to 4 leaflet pairs and one terminal leaflet.  The leaflet edges have spiny teeth and prominent veins on their lower surface.  From February to April yellow flowers appear, producing small orange-red fruits in early summer.  In addition to its leaf arrangement, Texas Barberry differs from Agarita in terms of range.  While it occurs in the Edwards Plateau and in one location in the Texas Panhandle, it is endemic to the Hill Country region, where it grows in full sun to light shade on ridges with rocky, limestone soil.  Texas Barberry is also rare and much less common than Agarita, and its foliage turns reddish-purple in the fall.   

While both of these species of plants are often grown for their spiny evergreen foliage and yellow flowers in early spring, their fruits are edible for humans (as well as wildlife) and are rich in vitamin C, and have been used to make jellies, pies, cobblers, and wines.  While edible, the fruits are highly acidic and should not be eaten raw in large quantities.  Additionally, the wood of these species has been used as a light yellow dye for wool.  

Whether you are looking for a barrier plant, wildlife cover, early bloomer, edible fruits, or just something evergreen that requires little care, look no further than our native, marvelous Mahonias! 

A Thistle Epistle

Mexican Yellow nectaring on Texas Thistle

As one of the most wrongly maligned and misunderstood group of wildflowers, native thistles have never been truly embraced, not even by wildscape gardeners or habitat restoration practitioners. While these plants play a significant role in our ecosystems, they have been a direct casualty of habitat loss, first by plow-based agriculture and followed by the continual development of roads and cities.  Further, recent invasions of non-native, exotic thistle species and the inability to discern them from the superficially similar native species, have contributed to their unjustified reputation and ongoing demise.

Texas Thistle, Cirsium texanum

Native thistles are a beautiful and important group of plants, with subtle blue-green foliage, fascinating stem and leaf architecture, and long-lasting pastel blooms that nourish many species of insects and birds.  The nectar they produce is utilized by many species of bees, wasps, butterflies, moths, flies, beetles, spiders, katydids, and hummingbirds, which demonstrates the wide diversity of animals supported by native thistle flowers.  In late summer and early fall, they are an essential nectar source for migrating Monarch butterflies. Their persistent seed heads provide the favorite food of goldfinches (both Lesser and American) and other songbirds such as the Carolina Chickadee, and the silky fluff attached to mature seeds is used to line their nests in the spring. 

Silvery bracts of the Texas Thistle

While there are many plants with spines that are erroneously called ‘thistles’, true thistles belong to the genus Cirsium. Of the 62 native species in North America, the most important species in our area are the Texas Thistle (Cirsium texanum) and the Yellow Thistle (Cirsium horridulum).  The Texas Thistle, also called Southern Thistle or Gray Woolly Twintip, is an upright, unbranched or sparingly branched plant, 2 to 6.5 feet tall, with grayish-green foliage that is spiny and woolly-white below.  Violet-pink to deep lavender-rose composite flower heads top the stems from April to August, and are surrounded by bracts that bear a silvery strip down the middle.  Texas Thistle is also the larval host plant for the Painted Lady and Mylitta Crescent butterflies.  

Yellow Thistle, Cirsium horridulum

Yellow Thistle, as perhaps foreshadowed by its scientific name, has a host of other, undeserved common names such as Horrid Thistle and Terrible Thistle.  It has a branching, densely hairy stem rising from a 2 foot wide basal rosette, 1 to 5.5 feet tall, with long grayish-green spiny leaves and several large flower heads.  Blooming May to August, these composite flower heads are up to 3 inches wide, surrounded by a whorl of spiny, hairy, leaf like bracts, and are frequently red-purple, pink, or white instead of the namesake yellow.  In the first year of growth this plant remains a low-lying rosette, and ‘bolts’ in the spring of the following year to reach its full height.  Yellow Thistle is an excellent attractant for Sphinx moths and is the larval host plant for the Little Metalmark and Painted Lady butterflies.  

Texas Thistle seed head

It’s time to bring back our native thistles, so this fall consider planting them in your wildscape. These species have evolved with our native pollinators in our natural habitats over thousands of years.  As a result, they benefit us by helping to sustain a healthy ecoweb, protecting our water quality, sequestering carbon in our soils, and adding a sublime beauty and structure to our landscapes.  And that’s our epistle to the thistle! 

Sun Trackers

This time of year, the most notable family of plants are the Heilianthus, or sunflowers.  From the Greek ‘helios’ or sun and ‘anthos’ or flower, these plants are usually tall annuals or perennials that during their growth phase exhibit a subtle behavior in the daylight hours.  This behavior, called heliotropism, is the ability for the young flower buds and leaves to gently tilt toward the sun, tracking it as it moves across the sky. By the time the flower heads mature, they are stationary but generally facing east to greet the rising sun.

Sunflowers are typically tall plants with one to multiple flower heads, consisting of bright yellow ray florets or flowers, surrounding yellow or maroon disc florets.  In wild or native species, the rough and hairy stems are normally branched, and the leaves are often sticky and lance or heart-shaped. Sunflowers also exhibit phyllotaxis, or the arrangement of leaves on a stem that forms a distinct pattern, in this case a repeating spiral.  Additionally, the disc florets also display a phyllotactic pattern, one that creates the optical effect of criss-crossing spirals in the flower’s center.

Common Sunflower (Helianthus annuus)

In our area, the two most abundant sunflowers are the Common Sunflower (Helianthus annuus) and the Maximilian Sunflower (Helianthus maximiliani).  Blooming from May to October, the Common Sunflower grows on dry soils, especially in disturbed areas.  It can reach 1.5 to 8 feet tall, and various parts of the branched stems can be either green or dark purple.  The heart-shaped leaves are coarse and covered in rough hairs, and grow from 2.5 to 10 inches long.  Up to 4 inches across, the flower heads have yellow ray flowers and reddish brown disc flowers.  As their scientific name suggests, these plants are annuals.

Maximilian Sunflower (Helianthus maximiliani)

Maximilian Sunflowers, on the other hand, are perennials that bloom in September and October. They grow 1 to 6 feet tall in colonies on both the dry ground of prairies and the moist ground of roadside ditches and other low places.  Shorter, rough hairs cover the narrow lance-shaped leaves, which average 2 to 4 inches long.  The 1.5 to 3 inch wide flower heads have yellow ray flowers surrounding yellow disc flowers, with numerous flower heads growing along the unbranched stems.

Aside from their aesthetic value to humans, sunflowers are generally palatable to deer and numerous species of birds eat their seeds.  Their flower heads support nectaring bees, and they are the food plants for several butterfly species such as the Bordered Patch and Silvery Checkerspot.  When mixed with other native annuals, these sun trackers provide good cover for many species of wildlife, and would be a great addition to your native wildscape.