Corn Lilies, Cyclops Lambs, and Sonic the Hedgehog

Photo by Judy Gallagher licensed by cc-by-2.0

1957 was an alarming year for Idaho ranchers. Some herds of sheep were giving birth to lambs with severe deformities. The lambs simply weren’t developing right. They emerged from the womb sporting limbs from their heads, incomplete brains, and some of them had only a single, malformed eye in the middle of their face. It would take over a decade before the cause of these deformities was identified and another two decades before we knew why it happened. The first line of evidence came from the weather patterns during that fateful year.

In an average year, sheep usually find enough forage at lower elevations. With plenty of rain keeping plants happy and lush, the sheep don’t have to travel far to find food. Things change during severe droughts. As droughts worsen, plants at lower elevations start to disappear. To find enough food, sheep will move up in elevation where plants are not yet affected by drought. However, the move up slope coincides with a change in the presence and abundance of some plant species. Notably, species like the corn lily (Veratrum californicum) are more prevalent at higher elevations.

Photo by Clint Gardner licensed by CC BY-NC-SA 2.0

Now if there is one common thread that winds its way through the genus Veratrum, it’s the fact that all members produce some seriously potent alkaloid compounds. Though toxicity can vary from species to species, it is a safe bet that most Veratrum can harm you if ingested during their active growing period. However, despite the fact that all parts of Veratrum are toxic, it appears that these Idaho sheep were a bit desperate. It was discovered that during the drought of 1957, some sheep were feeding on the flowers of the V. californicum.

A deformed lamb showing the single, malformed eye and the anomalous limbs.

The flowers themselves aren’t the most toxic part of the plant but they produce measurable levels of toxic alkaloids. After 11 years of studying these malformed sheep, scientists realized that although pregnant sheep could feed on the flowers of V. californicum with no ill effects, they would go on to give birth to the deformed lambs. It became readily apparent that the deformities found in these lambs could be traced back to the consumption of V. californicum.

However, this was not case closed. The ranchers learned that they must keep their sheep away from Veratrum but no one had any idea as to how eating these plants led to such horrible birth defects. It took 25 more years before scientists had that answer.

While studying embryonic development in fruit flies, researchers discovered a set of genes that, when deactivated, cause the flies to grow spiny hairs all over their body. They named this gene “Sonic Hedgehog” after the spiky blue video game character. It turns out that the Sonic Hedgehog gene was extremely important in the development of more organisms than just flies. Importantly, these genes control the way in which the body plan of an organism develops. When something goes wrong with the Sonic Hedgehog pathway, a whole slew of deformities follow. Among these is the development of a single, malformed eye on the middle of the mammalian head.

Luckily, researchers studying Sonic Hedgehog remembered the story of the cyclops sheep in Idaho. It didn’t take long to put the puzzle pieces together. It was soon realized that V. californicum produces one alkaloid in particular that interferes with Sonic Hedgehog. The compound was given the name “Cyclopamine” as a reference to the deformities is caused in those sheep back in 1957. Scientists finally had the smoking gun.

The molecular structure of Cyclopamine

When droughts caused sheep to moved into the mountains in search of plants to munch, some of them would nibble on the flowers of V. californicum. If they were pregnant at the time, enough Cyclopamine made it into their system that it would shut down the Sonic Hedgehog gene pathway in their developing offspring. Once that pathway is shut down, the embryo no longer has a sound blueprint for development and all of those horrendous deformities take place.

The story does not end here. Not only was a 30+ year mystery solved, scientists had come away with a far more detailed understanding embryonic development. They also walked away with some new ideas to test. The most exciting of these involves cancer treatments. It turns out, the Sonic Hedgehog pathway is one of the many pathways involved in a couple different kinds of cancer. Normally, Sonic Hedgehog is dormant in adults but certain circumstances can see it reactivate and go into overdrive, leading to cancerous tumors. Some scientists are now using Cyclopamine to turn off the Sonic Hedgehog pathway in those tumors as a form of cancer treatment.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] [3]

Giant Hogweed And Other Toxic Plants

Photo by Jean-Pol GRANDMONT licensed under CC BY 3.0

Everybody run, giant hogweed is coming! I am sure by now, many of you reading this will have picked up a story or two about a nasty invasive plant that will render you blind and nursing third degree burns. Indeed, giant hogweed (Heracleum mantegazzianum) is a plant worth learning how to identify. However, the tone of these articles is often one of hysterics, leaving the reader feeling like this plant is more like a Triffid, actively uprooting itself to hunt down unwary humans. Is giant hogweed worth all of this anxiety?

Let's start with the plant itself. Giant hogweed is a member of the carrot family (Apiaceae). Its native range encompasses much of the Caucasus region and into parts of central Asia. It was (and probably still is in some areas) considered a wonderfully large and unique addition to a temperate garden. And large it is. Individual plants regularly reach heights of 6 feet (2 m) or more and some records indicate that individuals over 10 feet (3 m) in height are not unheard of.

Photo by Jean-Pol GRANDMONT licensed under CC BY 3.0

Because it was once a popular garden plant, this species has been introduced far outside of its native range. For many decades, giant hogweed probably lurked in the background unnoticed, its seeds finding favorable spots for germination among other weedy plants along roadsides, fallow fields, and abandoned lots. In the last few years it has grown harder to ignore. More and more plants are showing up where they shouldn't. Indeed, it seems that giant hogweed is yet another invasive species we need to get on top of. But what about all of that panic? Certainly its invasive status alone isn't what all the hype is about.

Well, like all members of the carrot family, giant hogweed produces an impressive array of chemical compounds. Many of these compounds serve to protect the plants from hungry herbivores and a plethora of microbial infections. Some of the compounds in the giant hogweed arsenal are a group known as the furocoumarins. These compounds defend the plant in a rather alarming way. These furocoumarins are phototoxic, which means when the sap gets on the body of an animal and is exposed to sunlight, they cause severe chemical burns.

Stories of people being hospitalized due to an unfortunate run in with this plant make headlines wherever it pops up. That being said, simply touching the plant isn't going to hurt you. The chemicals are sloshing around in the sap of giant hogweed and the plant needs to be injured in some way before they will leak out onto whatever is hurting it. For humans, this usually occurs while mowing or weed whacking, or if a child mistakenly uses the hollow stem as a pea shooter.

With stories like this floating around, it is no wonder then why people get so upset when this plant shows up. However, I can't help but feel that this is being fed on a bit by media fear-mongering. It is worth putting giant hogweed into some practical context. It may actually alarm you to know just how many plants on the landscape have the ability to cause you harm if handled the wrong way.

Wild parsnip (Pastinaca sativa). Photo by USFWS Midwest Region

Even hogweeds less robust relatives are capable of causing phototoxic reactions. I once weed whacked a large patch of Queen Anne's lace (Daucus carota) and wild parsnip (Pastinaca sativa) and ended up covered in nasty blisters the next day. I recovered but I sure did learn to give those two species more respect whenever I encountered them. Plants like poison ivy, oak, and sumac certainly cause their fair share of misery but even these do not get the sort of media attention that giant hogweed does.

Even more interesting are some of the species we actively plant in our gardens. For instance, castor bean (Ricinus communis) is quite popular among gardeners and it is responsible for producing ricin, a protein with enough killing power to bring down an adult human many times over. Take a bite out of the castor bean in your garden and it will be the last thing you ever eat. Even more potent than ricin is aconitine, an alkaloid produced by beloved garden plants like the monkshoods (Aconitum spp.) and the larkspurs (Delphinium spp.). This powerful alkaloid causes your nervous system to endlessly fire, leading to convulsions and death.

Castor bean (Ricinus communis). Photo by Jason Hollinger licensed under CC BY 2.0

Similarly, a few different species of Datura are commonly grown around the world. Datura posioning is nothing to mess with and symptoms include "a complete inability to differentiate reality from fantasy; hyperthermia; tachycardia; bizarre, and possibly violent behavior; and severe mydriasis (dilated pupils) with resultant painful photophobia that can last several days." Even plants we grow for food can hurt us in bad ways. Most members of the tomato family produce a multitude of toxic alkaloids like solanine. That is why only ripe tomatoes and eggplants should ever be consumed.

Jimsonweed (Datura stramonium). Photo by Al_HikesAZ licensed under CC BY-NC 2.0

In reality, I could devote an entire blog and podcast series to the chemical warfare plants have taken up during their long and complicated evolutionary history. Long story short, plants are sessile organisms that must defend themselves in order to survive and toxic chemicals are really great means to do just that. The reality is that we welcome many toxic and potentially harmful plants (both knowingly and unknowingly) into our lives and it seems slightly odd that species like giant hogweed warrant such fervor from media outlets. That being said, it is important to treat these plants with the respect they deserve. Don't bother them and they won't bother you.

So, is giant hogweed coming to attack you and your family? No. Is giant hogweed a plant worth learning to identify? Yes. Is giant hogweed dangerous to humans? Yes, but only under certain conditions.

Plants like giant hogweed are the perfect reminder as to why we must give plants more respect in our society. Teaching friends and family which plants can feed them and which plants can hurt them is something everyone should invest some time in doing. If you find giant hogweed in your area and you do not live in the Caucasus or central Asia, don't be a hero. Call a professional to come and deal with it. Otherwise, stay calm and keep on botanizing. Giant hogweed is not out to get you.

Photo Credits: [1] [2] [3] [4] [5] [6] [7]

Further Reading: [1] [2] [3]

Understanding the Cocklebur

Photo by Dinesh Valke from Thane, India licensed under CC BY-SA 2.0

Spend enough time in disturbed areas and you will certainly cross paths with a cocklebur (Xanthium strumarium). As anyone with a dog can tell you, this plant has no problems getting around. It is such a common occurrence in my life that I honestly never stopped long enough to think about its place on the taxonomic tree. I always assumed it was a cousin of the amaranths. You can imagine my surprise then when I recently learned that this hardy species is actually a member of the sunflower family (Asteraceae). 

Cocklebur doesn't seem to fit with most of its composite relatives. For starters, its flowers are not all clustered together into a single flower head. Instead, male and female flowers are borne separately on the same plant. Male flower clusters are produced at the top of the flowering stem. Being wind pollinated, they quickly dump mass quantities of pollen into the air and wither away. The female flowers are clustered lower on the stem and consist of two pistillate florets situated atop a cluster of spiny bracts. 

After fertilization, these bracts swell to form the burs that so many of us have had to dig out of the fur of our loved ones. Inside that bur resides the seeds. Cocklebur is a bit strange in the seed department as well. Instead of producing multiple seeds complete with hairy parachutes, the cocklebur produces two relatively large seeds within each bur. There is a "top" seed, which sits along the curved, convex side of the bur, and a "bottom" seed that sits along the inner flat surface of the bur. Studies performed over a century ago demonstrated that these two seeds are quite important in maintaining cocklebur on the landscape. 

Photo by Dinesh Valke from Thane, India licensed under CC BY-SA 2.0

You see, cocklebur is an annual. It only has one season to germinate, grow, flower, and produce the next generation. We often think of annual plants as being hardy but in reality, they are often a bit picky about when and where they will grow. For that reason, seed banking is super important. Not every year will produce favorable growing conditions so dormant seeds lying in the soil act as an insurance policy. 

Whereas the bottom seed germinates within a year and maintains the plants presence when times are good, the top seed appears to have a much longer dormancy period. These long-lived seeds can sit in the soil for decades before they decide to germinate. Before humans, when disturbance regimes were a lot less hectic, this strategy likely assured that cocklebur would manage to stick around in any given area for the long term. Whereas fast germinating seeds might have been killed off, the seeds within the seed bank could pop up whenever favorable conditions finally presented themselves. 

Today cocklebur seems to be over-insured. It is a common weed anywhere soil disturbance produces bare soils with poor drainage. The plant seems equally at home growing along scoured stream banks as it does roadsides and farm fields. It is an incredibly plastic species, tuning its growth habit to best fit whatever conditions come its way. As a result, numerous subspecies, varieties, and types have been described over the years but most are not recognized in any serious fashion. 

Sadly, cocklebur can become the villain as its burs get hopelessly tangled in hair and fur. Also, every part of the plant is extremely toxic to mammals. This plant has caused many a death in both livestock and humans. It is an ironic situation to consider that we are so good at creating the exact kind of conditions needed for this species to thrive. Love it or hate it, it is a plant worth some respect. 

Photo Credits: [1] [2] 

Further Reading: [1] [2]