Nettles

Spurge Nettle (Cnidosculus stimulosus) grows in dry,
sandy soil.  This plant was one of a group in Weymouth Woods State Park,
Moore County, North Carolina.

When I hear the word nettle, my skin starts to itch.  The name accurately describes what these plants do.  Brush up against a nettle and you get pain, itching and inflammation.  Hairs on the stems and leaves of nettles may contain powerful toxins that cause a painful reaction called urticaria.  The plant structures that cause this uncomfortable condition are urticating hairs.  There are several plants in the Southeastern United States called nettles, but they are not closely related to each other.  All these nettles share a common feature, hairs or spines on the stems and leaves.  These structures often contain noxious chemicals and deter grazing animals.  

Solanum carolinense or Horse Nettle is a relative of potato and tomato. 
Horse Nettle is a common plant in fields and along roadsides. 
Rowan County, North Carolina.

A closeup view of Horse Nettle flowers with their five white
petals and five bright yellow anthers.
Rowan County, North Carolina.

Horse Nettle (Solanum carolinense) is a member of the Nightshade family, the Solanaceae.  This family  family includes many familiar plants; potato (Solanum tubersum) and tomato (Solanum lycopersicum), tobacco (Nicotiana tabacum) and Deadly Nightshade (Atropa belladonna).  Horse Nettle is a low-growing herb with lobed leaves.  The leaves and stems bear hairs and large hooked spines.  Horse Nettle produces blueish-white flowers that have five petals and five bright yellow anthers.  The fruits look like yellow cherry tomatoes and each contains dozens of seeds.  Horse Nettle is one of the most toxic plants in this part of the world because they produce solanine glycoalkaloids.  When ingested solanine glycoalkaloids cause nausea, vomiting, headache and even death.  These toxins are in the leaves, stems and fruits, so no part of the plant is safe to consume.

 

Horse Nettle leaves and stems have large spines. 
Rowan County, North Carolina.  

A maturing fruit of Horse Nettle looking very
much like its close relative, tomato.
Rowan County, North Carolina

The Horse Nettle fruit on the left is nearly ripe. The
others will turn yellow in a few days.
Rowan County, North Carolina.

Wood Nettle (Laportea canadensis) is a true nettle in the family Urticaceae.  Wood Nettle grows in Eastern North America near water as a member of the forest understory.  This plant has large bright green leaves that bear stinging hairs.  The hairs break off in the skin and release neurotoxins that cause sharp pain and raise a rash that can last for several days.  Despite their threat of pain, many people harvest and eat Wood Nettles.  These hardy folks boil the plants and this inactivates the toxins.  Wood Nettle is reputed to taste like spinach. 

 

Wood Nettle plant growing on the flood plain
of the Yadkin River.  Rowan County, North Carolina.

The stinging hairs of Wood Nettle.
These fine hairs contain toxins that give a painful sting.
Rowan County, North Carolina. 

The third species on this nettle tour is Spurge Nettle.  It has a marvelous scientific name, Cnidoscolus simulosus and grasping this plant is definitely a stimulating experience.  Spurge Nettle is in the family Euphorbiaceae and is primarily a plant of the Southeastern Coastal Plain where it grows in dry, sandy habitats.  This plant has large, dark green, lobed leaves and produces white flowers with five petals. The fruits of Spurge Nettle are capsules and each contains three seeds.  Of course, since it is a nettle, the leaves, stems and fruits are covered with urticating hairs that contain chemical irritants. Spurge Nettle has a large, starchy taproot that after boiling tastes like pasta.    

 

Spurge Nettle in flower.
Moore County, North Carolina.

Flowers and developing fruits of Spurge Nettle.
Moore County, North Carolina.

Closeup of the utricating hairs of Spurge Nettle.  
Moore County, North Carolina. 

The three-chambered fruit of Spurge Nettle.  Like the rest of the plant,
the fruits are covered with stinging hairs.
Moore County, North Carolina.

People all over the world have a complex relationship with nettles.  North American nettles may be poisonous, sting when touched and some are edible.  Folk medicine traditions describe many uses of nettle from treating asthma and kidney ailments to preventing baldness.  The Tibetan holy man, Milarepa, is said to have lived to a ripe old age in his mountain fastness by eating only nettles.  A side effect of this diet was his skin and hair turned green.  I make no recommendations on nettles as food or medicine, but they are attention grabbing members of our flora.   

The Sphinx, the Weed and the Parasite

 

Carolina Sphinx Moth (Manduca sexta) hovering
over the flower of Sacred Datura (Datura wrightii). 
The moth's proboscis is extended toward the flower.
Rowan County, North Carolina.

This is a story of the integration of three lives.  The sphinx is a giant moth whose caterpillar is a major agricultural pest.  The weed is Jimsonweed is a handsome plant with large showy flowers and produces hallucinogenic compounds.  The parasite is a wasp that lays its eggs in the larva of the Sphinx and new wasps burst forth like aliens from the chest of an unfortunate sci-fi character. 

 

Sacred Datura plant flowering at night.
Rowan County, North Carolina.

First the weed, Jimsonweed.  It goes by many names.  Its scientific name is Datura wrightii, also known as Sacred Datura and it is native to the Southewestern United States and Mexico.  We have several plants in our yard that came to us by way of Austin, Texas.  There are several Jimsonweed species and they are in the same family as potato, the Solanaceae.  This interesting and important plant family includes other well-known plants like Tomato, Tobacco, Eggplant, Pepper and Deadly Nightshade.

Sacred Datura is a desert plant with large gray-green leaves and, as expected from a desert plant, is quite drought tolerant.  It produces a variety of toxic alkaloids that when consumed can induce profuse sweating, drowsiness, visual impairment, hallucinations, psychosis and even death.   The sacred in the name comes from its use in religious ceremonies of native people in the desert Southwest and Northern Mexico.  One of the active compounds in Sacred Datura is scopolamine, a drug now used to combat motion sickness, usually in the form of a transdermal patch.  In the bad old days of spies and enhanced interrogation, scopolamine was a major ingredient in “truth serum” although its effectiveness is questionable.   

 

Early and nearly mature flower buds of Sacred Datura.
Rowan County, North Carolina.

Sacred Datura flower on the afternoon the
flower will open.
Rowan County, North Carolina.

Sacred Datura petals on a flower that is about to open.
Rowan County. North Carolina.

Jimsonweed produces abundant, large, white, trumpet-shaped flowers throughout the summer.  The flower shape and color give this plant another of its many common names, Angel Trumpet.   The flowers develop for several days, with the petals rolled up within the green sepals.  Each day the flower gets longer and finally on flowering day the petals emerge and turn white. In late afternoon, the flowers open to show the five petals fused that make the trumpet.  As evening comes, the flowers release a strong and pleasant fragrance reminiscent of gardenia.  The white color and fragrance gives a clue to what Sacred Datura is doing at night.  The plant is sending an unmistakable signal to its pollinator, the Carolina Sphinx Moth (Manduca sexta).  

 

Carolina Sphinx Moth about to feed.
Rowan County, North Carolina.

Carolina Sphinx Moth sipping nectar from a Sacred Datura flower. 
The moth's long proboscis is visible reaching into the flower.
Rowan County, North Carolina.

Carolina Sphinx Moth approaching a Sacred Datura flower.
Rowan County, North Carolina.

Carolina Sphinx Moth has a four-inch wingspan, is dark gray in color and has five paired, orange spots on the sides of its abdomen.  The moth also has a long proboscis, a feeding structure that can be over eight inches long.  The proboscis is the key to the moth’s relationship with the Jimsonweed.  Datura lures the moth in from a distance with is fragrance, gives a visual target with the white flowers. The payoff for the moth is the sugar-rich nectar.  The nectaries for the flower are at the base of the trumpet-shaped tube, eight inches down.  The Carolina Sphinx Moth hovers over and even flies into the flower to collect the nectar.  But collecting nectar is not straightforward.  In order to drink, the moth must thread its proboscis down one of five nectar tubes on the inside of the petals.  

Infrared video of Carolina Sphinx Moth feeding on Sacred Datura.

Rowan County, North Carolina.

More infrared video of Carolina Sphinx Moth feeding on Sacred Datura. 
Rowan County, North Carolina.

While collecting nectar, the moth brushes against the stamens of the flower picking up pollen.  It then flies to another flower and transfers pollen to the female stigma.  There the pollen makes a tube that grows through the stigma, down the style to the ovary at the bottom of the flower.  There the pollen nucleus fuses with the Datura egg.  The fertilized egg and surrounding tissue develops into the seed that is contained in the fruit.  The fruit of Sacred Datura is covered with spines and these give the plant yet another common name, Thornapple. 

 

Sacred Datura the day after flowering.
Rowan County, North Carolina.

Sacred Datura flower two days after flowering.
The sepals and petals have fallen off but the long
style and stigma are still attached to
the developing fruit. 
Rowan County, North Carolina.

The spiny fruit of Sacred Datura showing why another common
name for the plant is Thornapple.
Rowan County, North Carolina.

Mature fruit of Sacred Datura.  The fruit has broken open
and the seeds are visible.
Rowan County, North Carolina.

The Carolina Sphinx Moth comes from a large caterpillar called the Tobacco Hornworm.  This larval stage eats, as the name suggests, tobacco but also thrives on other plants in the same family, including tomato.  A female moth lays an egg on the host plant where the larva grows and molts several times. The final larval stage of Carolina Sphinx Moth is over three inches long and can quickly defoliate the host plant. 

 

Tobacco Hornworm is the caterpillar of Carolina Sphinx Moth.
This caterpillar is on a Tomato (Solanum lycopersicum) and is eating leaves.
The white structures are cocoons of the wasp Cotesia congregate 
that has parasitized the caterpillar.
Rowan County, North Carolina.

This is where the final part of the story comes in, the parasite.  Actually, it is a parasitoid wasp, Cotesia congregate, that injects its eggs inside the body of the Tobacco Hornworm caterpillar.  The wasp eggs hatch and the emergent larvae consume the caterpillar from within.  Two weeks later wasp larvae dissolve their way through the exoskeleton of the caterpillar and make a white cocoon on the outside. Within the cocoon, the wasps metamorphose into their flying form.  These wasps mate and parasitize more Tobacco Hornworms.  A caterpillar parasitized by Cotesia dies before it can transform into a moth so the wasp is an effective form of biological control for Tobacco Hornworm.  

This intricate relationship, this perfection of interaction, between the plant, the moth and the wasp has been honed for millennia by evolution. Sacred Datura attracts and feeds the Carolina Sphinx Moth.  The moth has the sensory system specialized to find the plant at night and a proboscis long enough to reach the nectar supply deep within the flower.  The moth then pollinates the Datura plant.  The wasp Cotesia parasitizes the Tobacco Hornworm to propagate the species.  All the interactions are pieces of an elaborate living puzzle.

POST SCRIPT - About two weeks after posting this blog I noticed the leaves of one of the Datura's were being eaten.  Sure enough, several larvae of Tobacco Hornworm were consuming the leaves.  

The leaves of this Sacred Datura have been eaten.  
Rowan County, North Carolina.

The Carolina Sphinx moths were not only collecting nectar and pollinating the flowers but were also laying eggs on the leaves.  Although it probably does not, this moth can complete its entire life cycle on one plant.  

The Datura leaves were being eaten by several Tobacco Hornworms,
the larvae of the Carolina Sphinx Moth.  Note this caterpillar has not been parasitized
by the Cotesia wasp and is very healthy, measuring in at 3.5 inches.

The Eyes Have It

 

A single inflorescence of Oxeye Daisy, Leucanthemum vulgare.
Yellow disc flowers are surrounded by white ray flowers. 
Rowan County, North Carolina.

Do you ever feel like you’re being watched?  Eyes may be upon you when you walk the woods or meadows.  Several plants in the Southeast got their names because they appear to have eyes.  

 

Blue-eyed Grass,  Sisyrinchium angustifolium flowers in the spring. 
Orange County, North Carolina.

Blue-eyed Grass (Sisyrinchium angustifolium) is the first of the eye plants to flower in the spring.  Blue-eyed Grass is not really a grass but is in the Iris family.  It is a monocot and has flower parts in threes, which is characteristic of that group.  Blue-eyed Grass has three blue petals and three blue sepals.  These petals and sepals look the same so, since there is not enough terminology in botany, they are called tepals.  Blue-eyed Grass leaves are long and narrow so they look like leaves of grass.  Between the blue flowers and the grass-like leaves, the name Blue-eyed Grass was obvious. 

 Two plants with eyes in their names that often occur together in summer fields are Oxeye Daisy (Leucanthemum vulgare) and Black-eyed Susan (Rudbeckia hirta).  Both these plants are in the Sunflower family, the Asteraceae.  

 

A group of Oxeye Daisies in a meadow.  Rowan County, North Carolina.

Despite looking All-American, Oxeye Daisy is native to Eurasia and came to our shores in the early 1900s.  It is now naturalized in the 49 continental states and most Canadian provinces.  Oxeye daisy  is a very successful plant and is considered an invasive species in some states. What appears to be a single flower is really a group of flowers, an inflorescence.   Oxeye Daisy inflorescences are made of two flower types.  The yellow eye in the middle is composed of dozens of disk flowers.  The disk flowers have greatly reduced petals but have pollen-producing anthers and the female carpel with its pollen collecting stigma. The outer rim of the inflorescence that looks like petals are really flowers, the ray flowers.  These flowers have carpels and five fused, white petals that stick out to the side. The ray flowers direct pollinators toward the central disk flowers.  

A single daisy disk flower.  It has five small yellow petals and a
two-lobed stigma above the petals.  The anthers are not visible 
in this picture.  Rowan County, North Carolina.  

Daisy ray flower with five white fused petals and
the stigma.  Rowan County, North Carolina.

This Oxeye Daisy has attracted a couple of predators.  On the right is a crab spider (family Thomisidae) 
and on the left is a ladybird beetle (family Coccinellidae).  Rowan County, North Carolina.

The original scientific name for Oxeye Daisy was Chrysanthemum leucanthemum bestowed by none other than Carl Linnaeus, the godfather of biological classification.  Linnaeus’s scientific name for Oxeye Daisy absolutely sings.  The genus and species names have the same number of syllables and they rhyme.  The original scientific name means “golden flower, white flower”.  Plant taxonomists revised the genus Chrysanthemum in the late 20^th century and renamed Oxeye Daisy Leucanthemum vulgare.  Quite a come down to go from “golden flower, white flower” to “common white flower”. 

 

A stand of Black-eyed Susan (Rudbeckia hirta). 
Rowan County, North Carolina

Black-eyed Susan is native to North America and grows over most of the continent.  It has black disk flowers and bright yellow ray flowers.  Black-eyed Susan flowers attract many pollinating insects and birds eat the mature fruits.

 

A single inflorescence of Black-eyed Susan with black disk flowers 
and yellow ray flowers.  Rowan County, North Carolina. 

Perhaps the strangest plant that might watch you is Doll’s Eyes (Actaea pachypoda).  This member of the Buttercup family grows in the eastern United States and Canadian provinces.  In North Carolina, it is most often found in mountain forests.  Doll’s Eyes produce white flowers in the spring and during summer makes white fruits with a single black dot that gives the plant its name.  Another common name for this plant is White Baneberry.  That name is a warning since the fruits and other plant parts are poisonous.  When eaten by people, Doll's Eyes fruits depress cardiac function and may cause death.  The toxins do not affect birds that eat the fruits and disperse the seeds of this interesting plant. 

 

A Doll's Eye plant with white fruits. Watauga County, North Carolina.

A closeup view of Doll's Eye fruits.  The fruits are white and spherical
and each bears a black spot that gives them their doll eye appearance.
Watauga County, North Carolina.

Be careful while hiking, these plants may be watching you.  The beauty of these plants may be in the eye of the beholder. 

 

Breaking My Own Rule

A Great Blue Heron (Ardea herodias) 
in a marsh at Paynes Prairie Preserve State Park, Florida.

As a rule, I do not help wildlife in distress.  I get calls from people, “A baby bird that has fallen out of the nest.  What should I do?”  I say, “Leave it alone.  They have to get out of the nest and the parents look after them.”  Or, “My cat brought in a chipmunk and it is hurt.  Should I call the vet?”  I say, “No. Put the unfortunate rodent outside and see what happens.”  This sounds harsh to my friends who know I love nature but that is how I usually approach this issue.  However, one time I broke my own rule. 

It was a Saturday morning in late summer and we were getting ready to leave for a quick, weekend trip to Atlanta to see Diane’s family.  Diane was filling the bird feeders when she noticed a Great Blue Heron (Ardea herodias) in our side yard.  We live in a suburban neighborhood in Salisbury, NC.  We don’t live on a lake or even a creek.  All the water we have on the property comes out of faucets. So it was highly unusual to see a Great Blue Heron in the yard.  We left for Atlanta with the bird standing next to our house. 

 

A Great Blue Heron hunting along a creek in
Clayton County, Georgia.

Great Blue Herons are magnificent birds.  They stand four feet tall and have a six-foot wingspan.  Their color is mostly blue-gray, with white on the neck and a sporty black streak across the face that in the breeding season ends in long plumes.  Great Blue Herons stand on long legs; have fierce yellow eyes and a dagger-like yellow beak.  They are a very successful species that are found throughout North America, Central America and the Caribbean. Great Blue Herons live near water; marine coastlines, rivers, lake shores, islands, swamps and marshes.  Their main food is fish but they will catch and eat all manner of small animals.  Great Blue Herons are striking when viewed in flight with their long neck tucked close to the body and their long legs trailing behind.  When I see one fly over I think, Pterodactyl. 

 

A flyover Great Blue Heron looking like a 21st century
Pterodactyl.  Moore County, North Carolina.

Diane and I got back from Atlanta on Sunday afternoon.  As we unloaded the car, I looked out the front door and saw the Great Blue Heron standing on our doorstep.  When I looked more closely at the heron I saw it had fishing line wrapped around its beak.  That is when I decided to break my own rule.  We would have to intervene and get this bird some help.  Monofilament line was a human intrusion in the life of this Great Blue Heron and another human intrusion was needed to make the situation right. 

 

The distressed Great Blue Heron at the bottom of
our front steps.  Salisbury, North Carolina. 

We rounded up a largish cardboard box and an old comforter from when our kids were little then went after the bird.  The heron was clearly weak and did not attempt to fly as we worked to corner it.  Just then, an SUV stopped in front of our house and out jumped Ryan who lived around the corner from us.  He said, “I am a licensed wildlife rehabilitator.  Do you need help?”  Of course, we needed help and gladly accepted.  The three of us combined to throw the comforter over the heron.  We examined the bird’s beak and cut the fishing line.  There was a bigger problem.  The line ran into the mouth and down the throat of this Great Blue Heron.  The bird swallowed a baited hook and it was lodged in its throat.  We dripped water into the heron’s mouth to rehydrate the bird as it glared at us.  Ryan said he would take the Great Blue Heron to a wildlife rescue facility and he bundled this big bird into the cardboard box then into his SUV along with a Labrador retriever who thought this was all perfectly normal. 

 

Close-up of the monofilament fishing line
wrapped around the heron's beak.  Salisbury, North Carolina.

Ryan, the wildlife rehabilitator catching the Great Blue Heron
in our yard.  Salisbury, North Carolina.

Ryan packing the heron in a box for transport to 
the rehab facility.  Salisbury, North Carolina.

A few days later, we looked on the wildlife rescue’s website and saw a picture of the heron.  I hope this bird made a full recovery and was released back into the wild.  I broke my own rule about interfering with wildlife because I thought the universe was speaking to me.  Of all the houses in the neighborhood, this Great Blue Heron showed up in ours.  Then it stayed around all day Saturday and Sunday and was waiting on the front porch when we returned from an out-of-state trip.  Then, as we were trying to catch the bird, a wildlife rehabilitator showed up to help.  Sometimes when the universe speaks, you have to listen. 

A wild and healthy Great Blue Heron in a salt marsh at 
Huntington Beach State Park, South Carolina.

 

Cedar-apple Rust

Cedar-apple Rust (Gymnosporangium juniper-virginianae), a parasitic fungus on

 Eastern Red Cedar (Juniperus virginiana). This wood gall produces orange, gelatinous horns

that produce spores of the fungus.

Walk by a Eastern Red Cedar (Juniperus virginiana) in the spring and you may see something weird.  Looking like an extraterrestrial invader among the cedar needles you could see gelatinous orange horns protruding from a small wooden ball.  This is one of the life stages of, not an alien, but a fungus, Cedar-apple Rust (Gymnosporangium juniper-virginianae).   

As the name suggests this fungus infects two different plant species to complete its reproductive cycle.  Some parasites, like the Small Pox Virus, infect only one host, humans.  An infected person would be the host for the virus and could pass the Small Pox Virus to other people.  Because it has a simple reproductive cycle and humans were the only host, a worldwide vaccination campaign has made this once deadly viral disease extinct in the wild.  Other parasites have a more complex life cycle.  The malaria parasite, the protozoan Plasmodium sp., requires two alternate hosts, a mosquito and a warm-blooded animal (like us) to go through its reproductive cycle.  Parasites with complex life cycles are harder to combat.  As its name suggests Cedar-apple Rust needs both a cedar tree and an apple tree, so its life cycle is more like that of malaria. 

 

Cedar-apple Rust on Eastern Red Cedar. The orange
horns are producing spores.  Rowan County, NC.

Cedar-apple Rust on Eastern Red Cedar. 
The orange horns have tried up on this gall. Rowan County, NC.

Cedar trees can have a long-term infection by the fungus.  Cedar-apple Rust spores, produced from the fungus infecting an apple tree, lands on the cedar.  A spore germinates and enters the stem of the cedar.  There is produces hormones that cause the stem to expand into a wood ball of tissue called a gall.  In early spring, the galls put forth their orange horns that bear spores and released them into the air.  The galls may produces several rounds of gelatinous horns during the spring, usually after rain.  Sometimes you can find the fungus covering a whole stem of a cedar.  Cedar trees may bear multiple Cedar-apple Rust galls.  We have one in our yard that looks like it is covered with Christmas decorations during the spring Cedar-apple Rust season. 

Cedar-apple Rust infecting Eastern Red Cedar stems. 
This rust has not yet induced the tree to make a gall.  Rowan County, NC.

An Eastern Red Cedar decorated with many spore
producing galls of Cedar-apple Rust.  Rowan County, NC.

Some of these spores produced on the cedar trees are lucky enough to land on the bud of an apple tree (Malus spp.) and infect the young leaves.  The Cedar-apple Rust infection on apple makes yellow lesions on the leaves.  During late spring and early summer, the fungus makes spores on the apple leaves that float through the air and can infect other cedar trees.  The spores made on the apple are different from those made on the cedar.  Cedar-apple Rust makes four different spore types during the course of its life cycle, only two of which made it into this blog.  Of course, the different spore types each have different names.  Mercifully, I will spare you these spore names. 

Cedar-apple Rust lesions on the upper surface of
an apple tree (Malus spp.) leaf Mecklenburg County, NC.

Cedar-apple Rust lesions on the lower surface of
an apple leaf.  Mecklenburg County, NC. 

Cedar-apple Rust infections can reduce fruit yield in apple orchards.  Apple growers try to remove cedar trees from near their orchards but it is nearly impossible to take out all the cedars trees in an area.  Most growers spray fungicides on their trees to control Cedar-apple Rust and other fungal diseases.   

We are now in the dog days of summer.  The apple phase of  Cedar-apple Rust is releasing spores. The cedar phase of the fungus is keeping a low profile. The galls on cedar phase will produce their strange orange horns again next spring.  Cedar-apple Rust, with its complex life cycle and bizarre spore bearing structures, is strangely beautiful.   This beauty is appreciated more by naturalists than by the apple growers who struggle to raise their crops in the presence of this fungus.