Last month, I wrote about grasses while spending all my days at home during the spring of the Covid-19 viral outbreak. Since then, between lawn mowing sessions and working from home, I awaited the return of my perrenial hosta plants from underground, which create a leafy landscape in the shady areas of my backyard. Now that we’ve reached the end of an academic year, summer is coming…and the hostas have spread their leaves!
Hostas (sometimes called “plantain lilies”) are perennial, shade-tolerant plants that are a popular choice in my area of North America for easy-to-grow landscaping. They’re so prevalent that they seem to now have a reputation for being a boring, rather predictable, and even uninspired choice for someone’s yard. But, here’s the thing: I actually love hostas, no matter how many eye rolls that might send my way. Why? They’re green and leafy and bring welcome life to the places that might otherwise be brown and uninhabited along the shady edges of a building, or under a tree. They’re easy to grow and maintain with little fuss. They’re hardy and can stand up to summer heat, winter cold, and our dog who occasionally runs through them or flops down on top of them. What’s not to like?
I won’t go into all the ins and outs of hosta lifestyles and growing requirements. There are plenty of quality websites for that type of thing, including this one from the University of Minnesota Extension program. Nor will I detail the thousands of different varieties of hostas here. But the variety of shapes, sizes, and colors of foliage is one of the things I like most about hostas. Detailed descriptions of about 150 varieties are available, for example, from the Missouri Botanical Garden…from “Abby” to “Zounds.” Hostas may be commonplace, but they’re not boring in their diversity!
One striking way that many of the hosta varieties can be distinguished from one another is by their variegation—two colors arranged in a pattern—such as the striped edges on some of my own hostas in the pictures above. As a geneticist, I find such color variation intriguing. The amount of green pigment can vary without a seeming cost to the overall health of the plant. How does this work behind the scenes, inside the leaves?
I’m not an expert on this topic, so I did a little reading to find out more. (If you’re interested in learning more, too, I’ll direct you to this overview from Stephen Rodermel and colleagues for a good summary of some of the more complex scientific background about variegation genetics.) In general, variegation in plants has been studied since the earliest years of plant breeding and genetics. As a visible trait that can be manipulated by genetic crosses, variegation prompted early curiosity and highlighted many unknown mechanisms. Famously, variegation of different kinds of pigments in corn kernels led biologist Barbara McClintock to the Nobel-Prize-winning discovery in the 1950s of segments of DNA that can move (or transpose) around the chromosomes. Understanding that genes can be unstable was an important breakthrough that continues to color our understanding of plant genetics, and even human disease.
Since McClintock’s time, we’ve learned even more about the complicated nature of plant genetics, including the idea that genes outside the chromosomes can impact visible traits. In leaf variegation, pale areas usually lack functioning chloroplasts—the subcellular compartments that act as tiny solar panels to power the construction of sugar molecules from carbon dioxide in the air. We can tell they’re not functional, even just looking from from the outside, because chloroplasts contain a pigment called chlorophyll, which absorbs red and blue light from sunlight and reflects green to your eyes. Dark green areas have plenty of chlorophyll for photosynthesis; white areas do not. Some genes involved in directing the manufacture of chloroplast structural components are housed as part of the chromosomes in the nucleus of the plant cell. Others are found on-site inside the chloroplast itself, remnants of a complicated evolutionary history of chloroplasts from ancient microbial ancestors. Any of these genes might have mutations that cause them to be less effective or useless. Or, some genes might instead be misregulated by other genes or molecules that change their behavior under certain conditions, leading to less chlorophyll overall.
Hostas come in so many shapes, sizes, and colors because they’ve been bred for these different features over the years. Given their popularity in landscaping, hostas have proliferated as a really good example of plant leaf variation, and scientists have been studying the underlying causes for a long time (I found, for example, this characterization of a genetic trait for spots on hostas back in 1980). Some of this work might explain the variegation patterns; other mechanisms account for different sizes, leaf shapes, etc. But the importance of understanding plant variation expands exponentially when considering other traits in other species, such as food crops. Leaf variegation is interesting for its own sake, of course, but understanding chloroplast function and its impacts on overall food yield extends well beyond the boundaries of my backyard.
It’s a “socially distant” holiday weekend in the United States this weekend, one usually spent with family and friends and backyard fun. Things are a little quieter this year as I and others give each other a little more space to help prevent a surge of coronavirus infections. But, my next-door neighbor offered up some of his hostas for my yard yesterday, if I feel like splitting sections of them with a trowel and transplanting them myself. That’s another terrific thing about hostas: you can add more plants to your yard from ones you already have on hand, because they spread by rhizomes (underground stems that put down new roots). And they’re apparently really helpful at providing physically distant neighborly interactions. That chore will have to wait for another day, however. I’m ready to enjoy both the emerging leafiness in my backyard and the return of summery weather relaxing on my porch instead. Have a safe and healthy holiday!