Plant science is endlessly fascinating and I often think we can learn as much from the controversies as for the so-called settled science. Below are two articles that explore a very controversial topic – can plants “see”. While biomimicry in plants is well known and well documented, the controversy arises on the question of whether plants have organs that actually allow them to “see” as our eyes allow us to see. The pro argument is based on recent work initiated by a citizen scientist in Utah and supported by several European researchers. Linda Chalker Scott presents the con argument in The Garden Professors Blog.
Can Plants See? In the Wake of a Controversial Study, the Answer’s Still Unclear: A tiny pilot study found that so-called chameleon vines mimicked plastic leaves, but experts say poor study design and conflicts of interest undermine the report. The vine Boquila trifoliolata is a shapeshifter. As it winds its way through the Chilean rainforest, its leaves change to resemble those of the plants it uses for support or, sometimes, neighbors it isn’t in contact with. It does such a good job of pretending to be other plants that although the vine was first described in the 1800s, its talent for impersonation remained secret until only about a decade ago. In the early 2010s, Ernesto Gianoli, a plant ecologist with the University of La Serena in Chile, realized that what appeared to be a strange-looking stem from a tree was in fact a B. trifoliata vine, the leaves of which perfectly blended in with the tree’s actual leaves. Once he saw that, he spotted the vine mimicking all sorts of plants—more than 20 species so far—by tweaking the size, shape, and color of its leaves. Gianoli reported his findings in a 2014 Current Biology paper, but to this day, no one is certain how B. trifoliolata pulls off its impressive masquerades. Most recently, he discovered microbiome similarities between the mimicking vines and their models, hinting that bacteria could be involved. But in a paper published online in Plant Signaling and Behavior, citizen scientist Jacob White and University of Bonn graduate student Felipe Yamashita claim to have found evidence for a different hypothesis: that the vines can “see” other plants’ leaves, at least well enough to copy their looks. Some found these results thrilling, while others were deeply critical. White, a homemaker in Utah with a passion for science and plants but with no formal scientific training, says he got the idea for the study after reading about the eye-spots of Chlamydomonas algae and the lens-like cells of certain cyanobacteria. he came across a 2016 mini-review by University of Bonn plant physiologist František Baluška and University of Florence plant neurobiologist Stefano Mancuso suggesting that plants have eye-like structures that afford them a form of vision. He read about botanist Gottlieb Haberlandt’s 1905 hypothesis that the upper epidermal cells of leaves may function as simple eyes (ocelli)—and about B. trifoliolata’s touchless mimicry. To eliminate the hypotheses about B. trifoliolata’s mimicry hinging on the transfer of biological compounds, he paired a B. trifoliolata plant with a fake for it to grow on. Lo and behold, he says he observed what appeared to be an attempt by the vine to mimic the fake leaves as it grew up the artificial plant. In correspondence, Baluška suggested he try a fake plant that looks more like something that could be found in Chile. White did, and the vine seemed to mimic it as well. The balance of this longish article details White’s further experiments, and critiques from peer reviewers.
The plants have eyes! Another foray into B(ad) S(cience): The article found here reports on the ability of leaves to mimic other leaves. While the concept of leaf mimicry is not new and has been seen in agricultural weeds for decades, this article goes a step further in claiming that plants can actually see the leaves they are to meant to mimic. But let’s back up a bit to explore leaf mimicry, which is a thing. Leaf mimicry serves to protect plants against herbivory and other types of removal (like weeding). This phenomenon was reported decades ago where agricultural weeds were shown to change their morphology to more closely resemble the desired crop. The benefit is obvious: if a weed looks like a crop plant, it is unlikely to be removed through hand weeding. Likewise, if a weed resembles a poisonous plant, herbivores that are visual learners will avoid these weeds. When some plants of a species are disproportionately allowed to survive (i.e., not eaten or removed), they reproduce better. Higher reproductive capacity means more offspring: this is the process of natural selection. We can even see this in dandelions in our lawns and gardens. Dr. Scott notes a number of clues that we’re dealing with bad science. There are a lot of problems with this paper; it would take me a separate blog post to critique the Materials and Methods section alone. But the biggest red flag for me was the following paragraph:
Each plant was assigned a number and placed on a growing rack. Two artificial vines were placed above the plants on a wooden trellis. During the winter, the plants grew quickly through the leaves showed poor mimicry of the artificial plants leaves. The original plant that we had did not show good evidence of mimicry until the spring and summer. We decided to continue the experiment and see if there were better results in the warmer months.
This reflects significant author bias: the experiment didn’t work in the winter, so they did it in the spring and summer to see if they got results they liked better. And apparently they did. Other potential red flags that careful readers might note include: a lead author with no apparent connection to an academic institution; a journal (Plant Signaling and Behavior) that focuses on the questionable field of “plant neuroscience”; an experiment performed under vague and uncontrolled conditions; and typos, grammatical errors, and awkward writing throughout.
As a counterpoint to her criticism, Dr. Scott includes this link to a wonderful video featuring the late, great Christopher Walken.