Thursday, December 21, 2017

Photosynthesis to the Rescue?

Every morning when the sun rises, millions of plants go to work converting solar energy to chemical energy, which they then use in the course of their lives for metabolism, growth, flowering, and so forth. We use it too, for we eat plants. So do our livestock, before we eat them. Even our fossil fuels started as photosynthesizing plants, as did plastics, and wood of course. Plants power the world, through clean renewable energy made from cheap abundant ingredients: water and carbon dioxide.
On a hot summer day in Kansas, millions of tiny chloroplast factories (upper right) are converting water and carbon dioxide into life-giving sugars and oxygen (source and source).
If plants can produce abundant cheap clean renewable energy, surely we clever humans can too. Bill Gates thinks so, as does the World Economic Forum (1). So do dozens of research groups currently working on artificial photosynthesis (AP):
“The benefits of artificial photosynthesis are numerous and include increased energy independence and efficient means of storing and dispatching of solar energy. Supporting the development of the foundational science and core technologies required for solar-fuel generation is the first step toward an investment in a future sustainable energy industry.” Joint Center for Artificial Photosynthesis
Artificial photosynthesis mimics photosynthesis in plants in a non-biological setting. Researchers are making good progress, but it probably will be at least a decade before you can buy an AP reactor.
Artificial photosynthesis in proposed twin-reactor system (Lee et al. 2013, modified)—not on Amazon just yet.
Photosynthesis is complex, but for this post, only the two basic steps are relevant: water splitting and carbon fixation. First water is split into hydrogen and oxygen, with oxygen released to the atmosphere. Next the hydrogen moves to the carbon fixation step. Atmospheric carbon dioxide is split, and carbon is combined with the hydrogen to make sugars, where energy is stored as chemical bonds. The sugars are broken down in respiration—providing energy for metabolism, growth, flowering, etc.—and carbon dioxide is released back into the atmosphere. The amount released is the same as that taken up in photosynthesis, so the overall process is carbon-neutral, and therefore “clean” (2) (3).
Basics of photosynthesis (source, modified).
Natural photosynthesis needs major tweaking to produce replacements for our fossil fuels. Sugars won’t do. And plants are inefficient at converting sunlight to chemical energy—only 0.1 to 8.0%, depending on temperature, type of light, and amount of carbon dioxide available. In contrast, mass-produced solar panels are 6 to 20% efficient. Researchers are addressing these limitations, and progress has accelerated recently thanks to new nano-scale methods and advanced materials.

Water splitting was achieved relatively early, and now is being improved in terms of cost, efficiency and durability. But the second basic step, carbon fixation, has taken much longer to replicate in the lab. Carbon dioxide must be split, and it’s an extremely stable compound. That’s why it accumulates in the atmosphere instead of breaking down. (Even if we were to switch completely to clean energy, the carbon dioxide already in the atmosphere won’t go away without active removal.)

Until recently, artificial carbon fixation produced only useless soups of 1-carbon compounds. But things have changed. With nanotechnology, AP components now can be designed down to the level of atoms, providing fine-scale control over function. Within the last two years, multiple labs have been able to split carbon dioxide to produce multi-carbon compounds in pure form (e.g. Kim et al. 2017).
How to make copper catalysts that fix carbon better than anything found in nature! (Kim et al. 2017, modified).

We now know that artificial photosynthesis will work, but continued research is needed to improve performance, reduce costs, figure how how to build suitable reactors, and more. Even if AP emerges successfully from research, it still has to cross the aptly-named Valley of Death, where many new technologies die before reaching commercial viability.
Traditionally governments fund research. Venture capitalists inhabit the Valley of Death, investing in high-risk projects in the hopes that at least a few will be high-yield.
New breakthrough technologies like AP are referred to as “blue sky” research—too early to know which will succeed in the real world. So if we are going to expand and diversify our energy portfolio, and make the transition to 100% renewables, we must invest in many blue sky candidates. And we must do it soon, because it usually takes decades for new technology to be widely deployed.

“But why bother?” you ask. “We’re already transitioning to renewables—solar and wind.” You’re absolutely right. Renewables are increasing fast. But they aren’t keeping up with growth in energy demand. “Despite decades of progress, about 80% of the world’s energy still comes from fossil fuels—the same as in the 1970s” (Rathi 2017). Even worse, today’s renewables are inadequate to make a full transition away from fossil fuels. The biggest challenge is in manufacturing, which contributes 20% of global emissions. Heavy load transport (shipping, aviation, land freight), which contributes 10% of emissions, also is out of reach of today’s renewables, due battery limitations (4).

“But is technology the only solution?” That question came up repeatedly in Energy Security, a terrific class offered by the International Studies Department, University of Wyoming (5). Whenever someone suggested conservation instead of technology, I flashed back on the late 60s and early 70s when Baby Boomers were conserving energy to save the planet. We even agreed to drive just 55 mph on the highways. Now we’re mega-consumers, contributing to fossil fuel’s relentless growth. Fossil fuels make for a wonderful life, and humans are not inclined to give them up, even those who agree that the amount of carbon dioxide (a greenhouse gas) being added to the atmosphere will warm the climate enough to destabilize the world on a grand scale.

It seems we must switch to renewable energy, not just to avoid climate change, but also to deal with the inevitable dwindling supply of fossil fuels. To do this, we need new innovative technologies … soon.
“The world has made remarkable progress in wind and solar over the past decade, and these technologies will continue to play an important role in our zero-carbon energy mix. … But because the scale of the challenge of providing reliable and affordable power without contributing to climate change is so vast, and the future energy needs are so great, we need to explore as many viable solutions as possible.” – Bill Gates, 2016


(1) Gates considers artificial photosynthesis to be one of three breakthrough technologies “that could solve the energy problem.” The Breakthrough Energy Ventures fund selected AP as one of seven innovation challenges, and the World Economic Forum and Scientific American included it on the list of “Top 10 Emerging Technologies of 2017.”

(2) “Clean” does not mean that photosynthesis is carbon-free, nor it does it necessarily remove carbon dioxide from the atmosphere on a net basis. Photosynthesis is sometimes mistakenly referred to as carbon-negative, probably because forests are widely recognized as Negative Emissions Technology (NET). Trees sequester carbon for hundreds of years (or longer if used for building materials) before death and decomposition return release it. Therefore on a human timescale, trees remove carbon from the atmosphere.

(3) Technically fossil fuels are carbon-neutral, for they originate as sugars produced through photosynthesis. Anaerobic fermentation of accumulated dead plant tissue produced the hydrocarbons we burn as fuel, releasing carbon “back” into the atmosphere. However, millions of years are required to produce hydrocarbons, much too slow to take up the carbon released in burning them. On a human timescale, the net effect is increased atmospheric carbon dioxide.

(4) Elon Musk of Tesla has challenged the view that current battery technology is unsuitable for large-scale applications. On November 16, 2017, he unveiled a prototype of an electric semi-truck able to travel 500 miles between charges at $1.26 per mile, compared with $1.51 for diesel. Skeptics immediately questioned his claims, but advance orders are coming in, starting with Walmart (15 trucks). Two weeks later, Tesla installed a battery at a wind farm in the state of South Australia, expected to power 30,000 homes. These batteries are immense. The semi-truck battery underlies the entire cab; the wind farm battery is the size of an American football field. It will be some time before either can be evaluated—at least a year for the trucks.

(5) I took advantage of UW’s policy of free courses for senior citizens. My final paper was about innovation in renewable energy, with artificial photosynthesis as a case study.


Bourzac, K. 2016 (November 21). “Will the Artificial Leaf Sprout?” Chemical and Engineering News. (accessed September 30, 2017).

Gates, B. 2016b (December 12). “A New Model for Investing in Energy Innovation.” Gatesnotes. (accessed December 1, 2017).

IRENA. 2017a. “Accelerating the Energy Transition through Innovation.” International Renewable Energy Agency. (accessed October 30, 2017).

Kim, D., et al. 2017. “Copper Nanoparticle Ensembles for Selective Electroreduction of CO2 to C2–C3 Products.” PNAS 114: 10560-10565.

Rathi, A. 2017 (December 4). “Humanity’s Fight against Climate Change is Failing. One Technology can Change that.” Quartz. (accessed December 15, 2017).

Friday, December 15, 2017

Guest Post: The Cactus Field(s) of Sheep Mountain

[Many thanks to Larry Haimowitz for this contribution! See bio at end of post.]
Driving to Sheep Mountain.
If you’ve ever driven west from Laramie to Centennial on Wyoming Highway 130 you’re likely familiar with this scene – that’s Sheep Mountain on the left. Most of the mountain is National Forest, but is surrounded by private property, which limits public access. You’ll find a very steep trail, just out of sight in this photo, near the NW corner of the mountain. Parking is very limited and there is no sign at the trailhead. Trails from the south end of the mountain have much gentler slopes.

Hiking Sheep Mountain, you can easily see half of all the kinds of cacti that grow in Wyoming. That’s not as impressive as it sounds: there are only seven species of cacti in the state (1, 2), three of which are certainly present on the mountain, and a fourth one that might be, though I haven’t found it yet. The most common of these are Opuntia polyacantha and Pediocactus simpsonii. The third, much less abundant, is Escobaria vivipara. You won’t have to walk more than a half mile from the trailheads at either end of the mountain to come across these three cacti, though you will have to look carefully to encounter E. vivipara. The fourth cactus, Echinocereus viridiflorus, if it is present, will be found around the base and lower slopes of Sheep Mountain.

For the most part, cacti on Sheep Mountain are solitary plants, spaced well apart from each other. Several years ago, I found an area so thick with cacti that I think of it as the cactus field of Sheep Mountain, and I think there are more just like it. I first discovered that place on a cold November morning.
A very steep trail starts from the NW corner of Sheep Mountain (above). On that particular morning, my faithful dog Tookie and I followed the fence that marks the western boundary of the National Forest (below).
The higher we went, the deeper the snow got.
After a while, we reached a windswept ridgeline, free of snow, and we started up the ridge because it was so much easier than walking in the deep snow. The ground was uneven and rocky underfoot, so I was constantly looking down to be sure of my footing. After what seemed like a long climb, I noticed something odd - little round balls of spines everywhere beneath my feet! Pediocactus simpsonii, so close together that it was hard to avoid stepping on them. There it was! A cactus field, a dense colony of Simpson’s ball cactus, covering several acres, something I’ve never seen the likes of.

Wind-blasted and sunbaked, with sparse, rocky soil, this highly exposed ridgeline looks like the most unlikely place for a plant to thrive. Oddly, in richer-looking habitats, Pediocactus is thinly scattered. I suspect that these cacti don’t like “wet feet” and need at least some full sun for development. The ridgeline would have better drainage and less competition from plants that shade the cacti.
This is what the plants looked like (above). Dormant for winter, they have lost water and shriveled to the ground to protect themselves from freezing, a common strategy for winter-hardy cacti. (Photo by Zoltan Kerner.)

Cacti of Sheep Mountain: Pediocactus simpsonii (Mountain Ball Cactus, Simpson’s Ball Cactus)
In the spring, the plants imbibe water and fatten up to prepare for flowering and growth. This is what they look like during the growing season. Plants may grow as single stems, rarely more than 4 inches in diameter, or clusters of two or more stems. Simpson’s ball cactus is the most abundant cactus on the mountain, and is widespread all over Wyoming and the intermountain west.
Close-up of Pediocactus stems.
Pediocactus simpsonii is one of three kinds of “ball” cacti in Wyoming that bear their spines on tubercles (also called nipples), which are easily seen in the photo above. The other two similar ball cacti belong to the genus Escobaria (1).
In our area, the plants start to bloom at the end of April and flower through the month of May. Flowers are about an inch across. Pink is the typical color, but there are occasional plants with white flowers.

Cacti of Sheep Mountain: Escobaria vivipara (Spiny Star, Pincushion Cactus)
Locally, Escobaria vivipara blooms later in May and into June, with flowers up to 2 inches across. Like Pediocactus, it grows as solitary plants or as clusters of stems, with each stem not more than a few inches in diameter, and it is also found over much of western North America.

How to tell the ball cacti apart:  The plants are easiest to tell apart when blooming. Escobaria vivipara has larger flowers with narrower petals, but this is not always a reliable character. A more definitive character is the origin of the flower buds. Flowers appear at the top of the plant in both of these genera, but on different parts of the tubercle. In Pediocactus, the flowers form on the tubercles next to the spines. In Escobaria, the flower buds are formed in the bottoms of the valleys between tubercles, far from the spines (1).

Cacti of Sheep Mountain: Echinocereus viridiflorus (Hedgehog Cactus, Green-flowered Hedgehog Cactus)
This is another small ball cactus, easily distinguished from the other two by spines that are born on ridges (referred to as ribs) instead of tubercles. Also, the flower buds develop lower on the plant instead of at the top (Yellow arrow pointing to rib with a flower bud). The green-flowered hedgehog cactus is found in the western Great Plains to the Rocky Mountains, from Texas and New Mexico to South Dakota and Wyoming.

The closest (to Sheep Mountain) recorded distributions of this plant are in the Laramie Range a little less than 20 miles east of Laramie (specimen here), and I have also found this plant to be abundant near the old stage stop of Virginia Dale, Colorado, 30 miles to the south. I have never seen Echinocereus viridiflorus on Sheep Mountain, but I suspect it may be present on the lower slopes. If you see it, I would love to hear from you.
The plant bears greenish-yellow flowers (hence the species name viridiflorus, meaning green-flowered) about an inch across in late May or early June. Notice how difficult it is to see the top of the plant, which is to the left of the flower – when not in flower, these ball cacti are often well camouflaged.

Cacti of Sheep Mountain: Opuntia polyacantha (Plains Prickly Pear)
This is the reason you don’t want to walk around in tennis shoes on our local prairies. (Photo by Marc Beckstrom.)
Plains prickly pear is very common in grasslands all over the state of Wyoming. It is considerably less abundant on Sheep Mountain than on the prairie, but is still quite easy to find. Opuntia polyacantha has one of the widest distributions of any cactus in North America, ranging northward from Texas all the way to Saskatchewan, and westward to British Columbia and Southern California. Like many wide-ranging prickly pears, this is a species that displays extreme variability in appearance in different regions.
Opuntia polyacantha blooms in June to early July in our area. The showy flowers are around 2 to 3 inches across and are usually a shade of yellow.

And now for the Rest of the Cacti of Wyoming

The three species of Wyoming cacti that are not found on Sheep Mountain include two prickly pears (Opuntia fragilis and Opuntia macrorhiza) and one ball cactus (Escobaria missouriensis). In Wyoming, Opuntia fragilis is known from Sweetwater County; Opuntia macrorhiza is known from the Great Plains and the Black Hills in eastern Wyoming; and Escobaria missouriensis is also known from the Great Plains and Black Hills, as well as Park County (1). More information about these species is easily found by searching the USDA Plants Database.

A Final Word on Cacti in Wyoming

If you consult Dorn and Dorn (1), you will find that they include an eighth species of cactus in Wyoming, Opuntia erinaceae, but I just told you that there are only seven species. Don’t be alarmed, Wyoming hasn’t lost Opuntia erinaceae since the Vascular Plants of Wyoming was published. It’s just that more recent taxonomic work has shown O. erinaceae to be a variety of O. polyacantha (2). Those wily Botanists!


(1) Dorn, Robert D. and Jane Dorn. Vascular Plants of Wyoming, 3rd ed. ©2001; pp 147-148. Distributed by the Rocky Mountain Herbarium.

(2) Lodé. Joel. Taxonomy of the Cactaceae. Published in Cuevas del Almanzora, Spain by Cactus Adventures, 2015.

About the Author

Larry Haimowitz is working on a graduate degree in entomology at the University of Wyoming, after retiring several years ago. His love of bugs, and all things in nature, goes back to his childhood on a farm. Now he carries a camera pretty much everywhere he goes, and intends to “keep on hiking, backpacking and climbing mountains until the day I die - but just a little bit slower each year.”
Tookie and Larry.

Monday, December 11, 2017

Tree Following, Road Following

Boxelder displays its oppositeness.

No surprise—the boxelder I’m following hasn’t done much since my report a month ago. But I took photos anyway. It’s a nice-looking young tree, with a canopy that should be full when it leafs out, probably in May or June.
The nook where it grows faces north and west, and gets little if any direct sun this time of year (I don't know because I never go there midday). So maybe the boxelder hasn’t been mislead by our "spring" weather—day after day with highs in the 40s F. This is quite mild for Laramie in December, at 7000 feet elevation in the continental interior. Prairie grasses in my yard are greening up, and some annual weeds have germinated and are growing. Maybe they'll die when true winter arrives, and I'll be weeding less next year (hah!).
Below the boxelder I did find changes—in accumulated trash. The inspirational message from last month was gone, with nothing particularly interesting replacing it (unless you are inspired by brake parts cleaner). Note persistent snow in the shade.

Meanwhile, there were major changes in the road construction project that I walk through every morning with my dog, and whenever I visit the boxelder. Last month, as I wrote my post, the Gomaco 6300 was being fired up to start on the bike path. Now it's done except for the section over the new bridge, which will go in next spring or summer. Though the road is closed to traffic, we can walk on it on weekends.
The amazing Gomaco 6300 on left, mid-photo.
The Gomaco 6300 truly is amazing! In laying the bike path, a concrete truck poured concrete ahead of it (between form boards) as it moved forward very slowly, vibrating and leveling as it went. Several workers followed, filling any low spots. Even more impressive, it can squeeze out curb-and-gutter! Concrete is poured into the machine, and out comes curb-and-gutter through a nozzle-like thing—like decorating a cake!!
The next day, after bike-path or curb-and-gutter work, three guys with big heavy saws cut joints. I have it on good authority (my brother, see note at end of post) that cut joints are prohibited in California, as sharp corners flake or spall with time. Instead, a large crew follows the machine, forming joints in the fresh concrete. But not in Wyoming, apparently. However, we do require major joints with expansion board, as in California.
Yellow paint marks where joints are cut in.
Expansion joint.
Close-up of joint with expansion board.
This road construction is underway (finally!) because we badly need a new bridge over the railroad tracks that split our town. I suppose construction of the bridge itself is far more complex and interesting than bike paths and curb-and-gutter, but I rarely see it. One of these winter months, while the boxelder is still “asleep”, I will include a bridge update in my monthly “tree” following report.
New road ascends to bridge, visible just left of trees.
New bridge under construction.

Note  My brother, in California, started his career as a concrete mason. Now, after 40 years, he supervises commercial projects with lots of concrete. He’s also a wonderful storyteller, so it’s not surprising that we had a 45-minute conversation about concrete adventures when I called to talk curb-and-gutter machines :-)

Many thanks to Pat of The Squirrelbasket for hosting our monthly tree-follower gatherings. Check out the latest news. Want to join us? More info here.

Monday, November 20, 2017

Quercity—Thoughts on Oaks

Coast live oaks, Quercus agrifolia, in the California Coast Range.

Free time has been scarce lately, so I’m offering a short post on oaks, inspired by “Querc-y Characters” at the Lady Bird Johnson Wildflower Center website.

I have a fondness for the Wildflower Center that surfaces at the least provocation, for I once talked plants with Lady Bird! It was 40 years ago, when I was botanist and sole employee of the Wyoming Natural Diversity Database. Jane Sullivan, wife of the governor, invited a small group of botanically-inclined ladies to gather for tea with Mrs. Johnson in Jackson Hole, at the base of the Grand Tetons. Conversation was awkward at first, but Lady Bird had done her homework, and as we introduced ourselves, she responded with what she had heard or read about our work. Soon we were happily discussing plants. Afternoon tea is not my idea of fun in the Tetons—I prefer hiking. But I really enjoyed my time with Lady Bird. She was so gracious and down-to-earth, a wonderful mix.

Now to the oaks …
Bur oak leaves, Dugout Gulch Botanical Area in the Black Hills.
In Wyoming, we have two oaks, both at the edge of their range here. Bur oak, Quercus macrocarpa, is a tree of the eastern and midwestern US that reaches its westernmost extent in northeastern Wyoming, mainly in the Black Hills. Gambel oak, Quercus gambelli, is common in Colorado and the southwestern US, but in Wyoming it grows only in the Sierra Madre, near Colorado. I was going to add “northernmost extent” but when I checked the NRCS PLANTS Database distribution map, I discovered that Gambel oak has been reported from South Dakota! However, there’s no county recorded, and the Forest Service FEIS treatment doesn't mention South Dakota. This would be a major disjunction, and news to me. But it’s an oak matter for another time.
Gambel oak; source.
In a way, we’re lucky we have just two oaks in Wyoming. I worked several winters in southeast Arizona, and struggled with the oak situation there. Apparently it’s even worse in Texas … or better, if you're not obligated to come up with identifications. Texas has more oak species than any other state in the US. Amy McCullough has put together an elegant straightforward guide to four of the common ones in Central Texas: Querc-y Characters, illustrated by Samantha N. Peters. Besides being a work of art, it shows clearly the characters and challenges in oak identification.
If you’re a hardcore oak fan, or looking for a botanical adventure, check out Quercus in the Flora of North America (FNA). There are 90 oak species in North America according to taxonomist Kevin Nixon, who prepared the FNA treatment. The exact number is debatable because oaks hybridize readily. “An astounding number of hybrid combinations have been reported in the literature, and many of these have been given species names, either before or after their hybrid status was known. … Hybridization in most cases results in solitary unusual trees or scattered clusters of intermediate individuals.” Oh dear!!

Even if you’re not up for a Querc-y Mega-Challenge, you might find Nixon’s introduction interesting—a revealing glimpse into the tortured world of oak taxonomists.
“A representative selection of mature sun leaves” is required for oak identification. Shade leaves won’t do. These are leaves of the coast live oak—sun above, shade below.

Monday, November 13, 2017

Boxelder—pest, pleaser, or provider?

Yesterday I went to check on “my” boxelder, the one I’m following. I’m limited to weekend visits, as weekdays belong to the Gustav A. Larson Company, which rents warehouse space next to the tree. Before I show you what I found, have a look at the road construction project en route, now almost a year ahead of schedule! It has been fascinating to watch.
This machine is laying down a bikepath as I write!

Now on to the tree. First, its habitat ...
The boxelder grows in a corner formed by north- and east-facing warehouse walls. The sun has moved far enough south now that it's shaded most (maybe all) of the time. Since last month, it has dropped most of its leaves; just a few dead ones hang on. Another difference: this visit was snow-free. In fact, we’ve been snow-free for almost a week, and it has warmed up enough to feel like fall again. I took advantage of the nice day to examine the boxelder more closely.
Dead leaves: petioles stay on longer than blades. Note opposite branching.
Oppositely arranged buds.
Sucker shoots up against the wall.
Urban habitat wouldn’t be complete without trash. I predict trash composition will change from month to month thanks to our wind. This time I found an inspiring message :-)

Following a tree provides the opportunity to learn about that species. My first stop along the knowledge pathway was the Biodiversity Heritage Library (BHL), “a consortium of natural history and botanical libraries that cooperate to digitize the legacy literature of biodiversity held in their collections and to make that literature available for open access ...” It’s my go-to place for interesting, fun, and often surprising information about plants. I like the emphasis on early pioneering botany, especially accounts by the explorers themselves.

A BHL search on Acer negundo returned 3843 hits. I sorted by date, browsed at the extremes, and found two interesting and contrasting accounts of the boxelder.

In 2013, Euardo Franceschi and Silvia Boccanelli reported that “spontaneous little forests” (núcleos boscosos espontáneos) of boxelder trees have developed in native Pampean grasslands in J. F. Villarino Park (Santa Fe, Argentina). Boxelder is a non-native and invasive pest species in Argentina, as well as in central Europe, China and Australia. In the Villarino grasslands, it’s clearly thriving. The researchers found overstories often to 40 ft in height (12 m), with boxelder common enough to be a dominant. Seedlings and small saplings were common in the understory, suggesting boxelder is there to stay in the absence of aggressive eradication.

François André Michaux, 1851; source.
At the other end of the BHL time line, I found boxelder in the The North American sylva, or A description of the forest trees of the United States, Canada and Nova Scotia by the pioneering French botanist and explorer François André Michaux (1770-1855). He made several trips to North America to botanize, beginning in 1785. In 1806, following detention in the Bermudas after being captured by the British, Michaux spent three years studying and collecting North American trees. After returning to France, he compiled his monumental work on the North American sylva—three volumes published 1818-1819. It was later translated by Augustus L. Hillhouse; this is the version I found at the BHL.

Below, “Box Elder or Ash leaved Maple” Plate XLVI. Courtesy Linda Hall Library Digital Collections. LHLDC was a great discovery. It provides online access to “significant rare and fragile materials” with free downloads.
Michaux explained that Ash leaved Maple was “a perfectly appropriate denomination,” but that general usage forced him use Box Elder, “though absolutely insignificant of any characteristic property of the tree.” Ash leaved Maple is perfectly appropriate because Acer negundo is indeed a maple, and the leaves are pinnately compound, looking a lot like those of ash trees. As is true for all maples, boxelder leaves are opposite on the stems. “The barren and fertile flowers [male and female] are borne on different trees” (i.e., dioecious).

Michaux found boxelder to be uncommon east of the Alleghenies, but “west of the mountains, on the contrary, it is extremely multiplied,” and abundant on floodplains. Especially interesting was his account of the reception the boxelder received in Europe post-introduction. Apparently humans jump-started its European invasion:
“Subsequently, it has spread into Germany and England, where it is in great request for adorning pleasure grounds, on account of the rapidity of its growth, and the beauty of its foliage, whose bright green forms an agreeable contrast with the surrounding trees.”
There are other reasons to like boxelders. Some botanists note that invasive species like boxelders provide ecosystem services in urban environments. Being an admirer of underdogs and the under-appreciated, I suspect I will become a fan of this tree.

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Franceschi, E., and Boccanelli, S. 2013.  Floristic-structural analysis of spontaneous little forests in the J. F. Villarino park (Santa Fe, Argentina). Bol. Soc. Argent. Bot. 48: 301-314.

Michaux, FA. (translated by Hillhouse, AL). The North American sylva, or A description of the forest trees of the United States, Canada and Nova Scotia ...