Here is a short story about my first encounter with twinflower (Linnaea borealis) back in fall of 2014.

"Summer and occasionally fall" is all I needed to read. So, I had a chance after all. After a few days of sitting in a kayak, musing over various wetland plants, I was excited to get my feet back on solid ground. The Adirondack Mountains offer seemingly endless opportunities for botanizers (and all nature nuts really) to meet new and exciting species that aren't often seen. For me, Linnaea borealis is such a species.

Commonly referred to as twinflower, this small plant is technically a dwarf shrub. In fact, it is a member of the honeysuckle family, Caprifoliaceae. Unlike its larger, more aggressive cousins, twinflower would be an easy plant to miss for most. It behaves much like partridge berry as it ambles over rocks and logs, never leaving the damp forest floor. Out of those who would pay it any mind, even fewer would consider this nondescript plant much to fuss about but those people have never seen this plant in flower.

During the warmer summer months, L. borealis puts on an unbelievable display. Each sprig of stem and leaves throws up a pair of bell-like flowers that will knock your socks off. Each flower is permanently aimed at the ground like tiny lampshades. The flowers are small and dressed in a mixture of white and pink but a large population in full bloom would be impossible to miss. There is something to be said about the beauty of small plants like this. Unlike larger, gaudy flowers, L. borealis forces its admirers to get down on its level to enjoy its full beauty. I like that in a plant.

Twinflower ambling over a rock in the company of some Cladonia lichen. — Twinflower ambling over a rock in the company of some *Cladonia* lichen.

The genus name "Linnaea" was given to this species in honor of the Swedish botanist, physician, and zoologist, Carl Linnaeus, who invented the binomial nomenclature naming scheme that we still use today. L. borealis has been said to be his favorite plant. As the specific epithet suggests, this species is circumboreal in its distribution. It is found in the northern forested regions of every continent in the northern hemisphere. It can also be found farther south but only at high elevation. These southern populations are disjunct relicts of the Pleistocene Epoch.

Pushed south by advancing ice sheets, boreal species like L. borealis took refuge at high elevation where climates were more similar to the far north. After the glaciers retreated, these populations were able to hang on in small pockets atop mountains. The most interesting thing about this is that L. borealis is not self compatible. It needs genetically different individuals to successfully set seed. In areas where only a small group of individuals represent an entire population, L. borealis has a hard time reproducing sexually. Such populations populations only persist via vegetative cloning. In places like Scotland, this has lead to some concern over genetic stagnation. Throughout the world, at the edges of its range, L. borealis has taken a hit from this genetic stagnation and its range is shrinking. As favorable climates continue to change, the relict populations atop mountains have nowhere to go and thus risk extirpation.

Despite all of this, L. borealis is one tough cookie. If you live where this plant is native, make sure to keep a watchful eye out for it when you are hiking. All too often it is trampled over by unwary hikers. If you are lucky enough to find a patch in bloom, get down on your hands and knees and really get to know this species. You will certainly be happy that you did.

Further Reading: [1] [2]

Long-lived trees face a lot of challenges throughout their lives. Many trees can live for centuries, which can be a problem because plants cannot get up and move when conditions become unfavorable. This should equate to a slower rates of adaptation and evolution for long lived trees but that isn’t always the case. Many trees are often superbly capable of adapting to local conditions. Recently, a team of researchers from the University of British Columbia have provided some insights into the genetic mechanisms that may underpin such adaptive potential.

Genetic insights came from a species of conifer many will be familiar with - the Sitka spruce (Picea sitchensis). Researchers were interested in these trees because they live for a long time (upwards of 500 years or more) and can grow to heights of over 70 meters (230 ft.). They wanted to understand how genetic mutations work in trees like the Sitka spruce because plants are doing things a bit different than animals in that department.

Plants are modular organisms, meaning they grow by producing multiple copies of discrete units. This equates to a branching structure whose overall shape is in large part determined by environmental influences. It also means that when genetic mutations occur in one branch, they can be carried on throughout the growth of those tissues independent of what is going on throughout the rest of the plant. This means that older trees can often accumulate a surprising amount of genetic diversity throughout the entire body of the plant.

Photo by Brandon Kuschel licensed by Creative Commons Attribution 3.0 Unported

When researchers sampled the DNA of tissues from the trunks and the needles of tall, old growth Sitka spruce, they were shocked by what they had found. From the base of the tree to the needles in the canopy, an old growth Sitka spruce can show as much as 100,000 genetic differences. That is a lot of genetic diversity for a single organism. Though plenty of other trees have been found to exhibit varying levels of genetic differences within individuals, this is one of the highest mutation rates ever found in a single eukaryotic organism. This could also explain why such long-lived organisms can survive in a changing world for their entire lives.

Now, it is important to note that many mutations are likely either neutral or potentially harmful. Also, the rates of mutation may differ depending on where you look on this tree. For instance, needles at the top of a Sitka spruce are going to be exposed to far more gene-altering UV radiation than bark tissues near the base. Still, over the lifetime of a single tree, rare beneficial mutations can and do accumulate. Imagine a scenario in which one branch mutation results in needles that are more resistant to say an insect pest. Those needles could hypothetically receive less damage than needles elsewhere on the tree. This odd form of selection is occurring within the lifetime of that tree and may even have implications for the future offspring of that tree thanks again to the quirks of how tree reproductive cells develop.

Many trees also do not have segregated germlines. What this means is that unlike animals whose reproductive cells develop from separate cell lineages than the rest of their body cells, the reproductive cells of trees develop from somatic cells, which are the same cells that form stems, leaves, and branches. This means that if a mutation occurs on the germline of a branch that eventually goes on to produce cones, these mutations can be passed on in the seeds of those cones. This obviously needs a lot of evidence to substantiate but now that a mechanism is in place, we know where and what to look for.

Photo Credits: [1] [2]