Pitcher's Thistle and the Dunes It Calls Home

Sand dunes are harsh habitats for any organism to make a living. They are hot, they are low in nutrients, water doesn't stick around for very long, and they can be incredibly unstable. Despite these obstacles, dunes around the world host rather unique floras comprised of plants well suited to these conditions. Sadly, we humans have been pretty good at destroying many of these dune habitats. This is especially true along the shores of the Great Lakes. To put this in perspective, I would like us to take a closer look at a special Great Lakes dune denizen. 

Meet Pitcher's thistle (Cirsium pitcheri). It is a true dune plant and is endemic to the shores of the upper Great Lakes. Its a rather lanky plant, often looking as if it is having a hard time supporting its own weight. Despite its unkempt look, adult plants can reach heights of 3 feet, which is quite impressive given where it lives. It is covered in silvery hairs, giving the plant a shiny appearance. These hairs likely protect the plant from the onslaught of sun, abrasive wind-blown sand, and desiccation. One of the benefits of growing in such inhospitable places is that historically speaking, Pitcher's thistle could grow with little competition. Individual plants grow for roughly 5 to 8 years before flowering. After seeds are produced, the plant dies. The seedlings are then free to develop without being shaded out. 

The last century or so have not been good to Pitcher's thistle. Shoreline development, altered disturbance regimes, and isolation of various populations have fragmented its range and reduced its genetic diversity. To make matters worse, its remaining habitat is still shrinking. Shoreline development has altered wave action that is vital to these dune habitats. Waves that once brought in new sediments and built dunes are largely carving away what's left. They are eroding at an alarming rate that even dune-adapted plants like Pitcher's thistle can't keep up with. Recreational use of these habitats adds another layer as heavy foot traffic carves deep scars into these dunes, furthering their demise. 

One silver lining in all of this is that dedicated researchers are paying close attention to the natural history of this species. They have discovered some fascinating things that will help in the recovery of this special plant. For instance, it has been observed that although trampling doesn't necessarily kill Pitcher's thistle, it does damage sensitive buds. This often results in plants developing multiple flower heads. Although this sounds like a benefit, researchers discovered that these damaged plants actually produce fewer viable seeds despite producing more flowers. 

Also, they have found that American goldfinches are playing a considerable role in its reproductive success. Despite the tightly clasping, spiny bracts that protect the seeds, goldfinches have been found to reduce seed production by 90% as they forage for food and the fluffy seed hairs for nest building. Evidence suggests that goldfinches are more likely to target small, isolated populations of Pitcher's thistle rather than large, contiguous patches. The reason for this is anyone's guess but it does suggest that they way around this issue is to supplement dwindling populations with new plants grown from seed. 

Without intervention, it is very likely that Pitcher's thistle would go extinct in the near future. Luckily, researchers and federal officials are teaming up to make sure that doesn't happen. Long term population monitoring is in place throughout its range and a sandbox technique has been developed for germinating and growing up new individuals to supplement wild populations. Through habitat restoration efforts, supplementing of existing and the creation of new populations, the future of this charismatic dune thistle has gotten a little bit brighter. It isn't out of the metaphorical woods but there is reason for hope. 

Photo Credit: [1] 

Further Reading: [1]

A Temporary Inland Sea in Northeastern North America


There are many species of small, nondescript spurge out there. All too often they go completely unnoticed, even by plant lovers like myself. As I have come to learn time and time again, every species has an interesting story to tell. That is why I started In Defense of Plants in the first place. The story I want to tell you today came to me from a chance encounter I had while exploring a beach on Lake Erie. I was musing over some tumbleweed I had found when I noticed some small spurge barely poking out of the sand around me. I took some pictures and moved on. Had I realized what I would come to learn from this spurge, I probably would have spent more time admiring it.

Our story begins roughly 18,000 years ago during the height of the last glacial period. Much of northern North America was buried under a massive glacial ice sheet. This was unlike anything we can witness on the continent today. In some spots the ice was well over a mile thick. The weight of that much ice on the land caused the bedrock underneath to compress, not unlike a mattress compresses under the weight of a human body. This compression pushed much of northeastern North America lower than sea level. Unlike a mattress, however, rock can take a very long time to rebound after the weight has been lifted. Around 13,000 years ago when the glaciers began to retreat, the land was still compressed below sea level. 


With the ice gone, the ocean quickly rushed in to fill what is now the St. Lawrence and Ottawa River valleys as well as Lake Champlain. A salty inland lake coined the Champlain Sea was the result of this influx of ocean water. For some time, the Champlain Sea provided seemingly out of place maritime habitat until isostatic rebound caused the land to rise enough to drain it some 10,000 years ago. During this period, the Champlain Sea was home to animals typically seen in the northern Atlantic today including whales, whose fossils have been found in parts of Montreal and Ottawa. Coastal plant communities formed along the shores of the Champlain Sea, which brings me back to my little spurge friend. 

Inland beach pea ( Lathyrus japonicus )

Inland beach pea (Lathyrus japonicus)

Sea rocket ( Cakile edentula )

Sea rocket (Cakile edentula)

The species in question is Chamaesyce polygonifolia, the seaside spurge. By no means rare, this obscure little plant is more typically found along the coast of the Atlantic. Along with other species like the inland beach pea (Lathyrus japonicus) and sea rocket (Cakile edentula), these plants followed the shores of the Champlain Sea and remained here in sandy, disturbed habitats ever since. These species are echoes of a brief period of time when North America was going through a lot of changes. Again, had I known this at the time, I don't know if I would have left the beach so quickly that day. I love to be reminded of how small we really are, how fleeting our existence really is. I love meeting species that are players in a much bigger story and Chamaesyce polygonifolia and company are just that. 

Photo Credits: [1] [2]

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