South Dakota Maples—Sugar, Silver, & a Trickster

Sugar Maple in Sica Hollow, northeasternmost South Dakota.

For April's tree-following report I'm sticking with my strategy of following (learning about) South Dakota trees—helpful in preparing our guide to trees and shrubs of the state. This month I chose maples, of which there are three.

South Dakota is not known for its trees. It's largely a prairie state, though much of what was prairie is now fields of corn, wheat, soybeans, hay, sunflowers and more. Most people who visit (i.e., tourists) head straight for the Black Hills in the far west, which are mostly covered in coniferous forest (that's why they look black).

But far eastern South Dakota also is forested. It's part of the immense Eastern Deciduous Forest (EDF) ecoregion, which covers the eastern third of the United States and extends into southeast Canada and northeast Mexico.

Globally, the North American EDF is one of the largest parts of the Temperate Broadleaf Forest Biome (yellow green). Source.

Authorities frequently claim that the EDF reaches its western limit in Minnesota, but they're wrong. It continues into South Dakota where it's best developed in the southeast and northeast corners of the state.

South Dakota land cover. Dark green units in the southeast and northeast are large stands of Eastern Deciduous Forest (modified from Johnson & Knight 2022).

EDF thrives where summers are warm and moist and winters are cold, as is the case in easternmost South Dakota (summers are increasingly dry going west). As the name indicates, the dominant trees lose their leaves each winter. These include oak, elm, basswood (linden), hackberry, and maples.

Eastern Deciduous Forest in northeast South Dakota, with a thick understory of young Sugar Maples hoping to reach the sky.

Of the three maple species in South Dakota, two are native to the far east—Sugar Maple and Silver Maple. However Silver Maple is widely planted, and escapees are occasionally found in the wild as far west as the Black Hills. The botanists who described and named these maples long ago chose very similar scientific names: Acer saccharum and A. saccharinum (thanks, guys, I hope I can keep them straight!). Both mean sugary, referring to the sap (Saccharum is the genus name for sugarcane). However the Sugar Maple's sap is far sweeter (Plant Finder, Missouri Botanical Garden).

These two maples are similar in appearance, enough so that some effort is needed to tell them apart. Both have what we think of as typical maple leaves—palmately lobed, like the fingers of a hand. Fortunately the details differ, which is more easily shown with photos than explained with words. But we intend to do both.

Leaves of Sugar Maple are more shallowly lobed with broader sinuses (gaps) between the main lobes. The sinuses usually are less than half the overall leaf length and are rounded at the bottom.

Sugar Maple, Acer saccharum (Minnesota Wildflowers Information).

Leaves of Silver Maple are more deeply lobed, and with narrower sinuses between the main lobes. The sinuses usually are at least half the length of the leaf and are more pointed at the bottom.

Silver Maple, Acer saccharinum (MWI).

Both trees develop furrowed ridged bark with maturity, but that of the Silver Maple is more flaky, enough to make it look shaggy ... or so they say. Do you have tips for telling these two maples apart? If so, please leave a Comment below.

Sugar Maple, Acer saccharum (MWI).

Silver Maple, Acer saccharinum (MWI)—a bit shaggy?

Now for those readers about fall off their chairs with curiosity ... there is indeed a third maple in South Dakota. But it's a trickster.

Yes, this IS a maple!

It's a maple with lobes so deep that they're leaflets.

This is Acer negundo, the Boxelder—also known as Ashleaf Maple (ash has similar leaves), Manitoba Maple, Érable à feuilles composées, and Poison Ivy Tree (not poisonous but leaflets are similar in shape). Instead of palmately lobed leaves typical of maples, it has pinnately compound ones—divided into paired leaflets with one more at the tip.

In contrast with Sugar Maple and Silver Maple, which are uncommon in South Dakota and limited to the far east, Boxelder is common and widespread across the state, and apparently not terribly picky about habitat. Some call it a weed.

The Boxelder I followed in 2018—a bit of wildscaping for this warehouse.

This is my contribution to the monthly gathering of tree-followers kindly hosted by The Squirrelbasket. More news here.

Sources cited

Johnson, W. Carter, and Knight, Dennis H. 2022. Ecology of Dakota Landscapes; past, present, and future. Yale University Press; Biodiversity Institute, U. Wyoming. ISBN 978-0-300-25381-8.

South Dakota Tree-Following—Prairie Crabapple

Pyrus ioensis. 1913, Curtis's Botanical Magazine. Source.

This month's tree-following report features another tree from South Dakota, part of my effort to learn more about the state's trees. There's a practical reason for this—I'm writing species descriptions and selecting photos for an online Guide to Trees, Shrubs, and Woody Vines of South Dakota.

Having recently worked my way through the challenging Rose Family (see post about the diverse and complicated fruits), a Rosaceaous tree was the obvious choice. I picked one new to me—Prairie Crabapple, Malus ioensis (formerly Pyrus ioensis).

I also wanted to showcase photos from Minnesota Wildflowers (now includes all plants not just wildflowers). It will be a major source of photos for our guide as our states share many species. Almost all their photos are free for non-commercial use (that would be us!), there are tens of thousands to choose from, and the photographers are botanists who know what's needed for identification. The Prairie Crabapple is a fine example (photos below are from the website).

Prairie Crabapples grow as shrubs or trees to 6 m tall, and can form dense thickets from root suckers.

Malus ioensis in bloom, hence the pinkish tinted crowns.

Prairie Crabapple leaves by Katy Chayka, creator and driving force of Minnesota Wildflowers.

With maturity, bark develops irregular ridges or plates that peel away to reveal reddish inner bark.

Prairie Crabapple flowers are typical of the Rose Family, with five showy-but-simple petals surrounded by five sepals. Inside the petals are numerous pollen-producing stamens surrounding a pistil containing ovules awaiting fertilization to become seeds.

Flower bud showing fuzzy sepals. These help with id.

Botanically speaking this crabapple is "armed", in this case with short branches that become sharp-tipped. Technically these are thorns, which are derived from branches or shoots (vs. spines which develop from leaves, and prickles which develop from the outer layer of a stem or branch; there's a Wikipedia article devoted to this topic).

Thorn developed from short flowering shoot.

Fruits of crabapples are pomes, from Old French "pome" meaning apple. Those of Prairie Crabapple are only about 2.5 cm across. They are "edible but barely so" according to Katy.

I'm looking forward to seeing Prairie Crabapple in the wild, of course! But there's a problem. Though multiple sources report it for South Dakota, I found NO specimens in a search of SEINet, the online portal to digital herbaria across the country. And the South Dakota Natural Heritage Program, which tracks rare plants, lists it as "Reported for woodlands of e SD, no vouchers yet found." I may be off on a treasure hunt once spring comes.

USDA Plants shows Malus ioensis in Lincoln, Clay, and Codington counties in South Dakota. Unfortunately no evidence or sources are provided (arrows added).

This is my contribution to this month's gathering of Tree Followers, kindly hosted by The Squirrelbasket. Once again—if you're looking for a good time, I invite you to join us!

Sources

Minnesota Wildflowers. Malus ioensis (Prairie Crabapple).

Flora of North America, Malus ioensis.

Fruits of the Rose Family—a Cornucopia!

How many Rosaceous fruits are in this painting? Answer at end of post. (Still Life with Fruit by Severin Roesen, 1852; Smithsonian Open Access)

The Rosaceae is a large cosmopolitan family of plants, with c. 3000 species scattered across every continent except Antarctica. It's best represented in the Northern Hemisphere, mainly in temperate habitats. This is a family much loved by humans. Gardeners have grown the "queen of the flowers" (the rose) for at least 5000 years, and we've enjoyed the diverse delicious fruits even longer.

Members of a plant family, even a large one, are supposed to be similar and often they are. For example, flowers of the vast majority of species in the Rose Family (excluding ornamentals) have five showy-but-simple petals surrounded by five green sepals. Inside the petals are numerous pollen-producing stamens surrounding one-to-many ovaries, each of which contains one or two ovules awaiting fertilization.

A typical Rosaceous flower: 5 sepals (green tips visible), 5 petals, many stamens (anthers at tips), and a cluster of numerous ovaries. (Wild Strawberry, Fragaria virginiana. Matt Lavin photo)

Unlike the flowers of the Rose Family—so similar and so simple—the fruits are diverse and often complex, in fact notoriously so. For centuries botanists have tried to subdivide the family based on fruit type. They've always failed.

By definition, fruits are mature ovaries containing mature ovules (seeds). But there can be so much more—thick flesh, plumose tails, tough skins, rock-hard coats, accessory structures, and aggregation. The Rose Family includes all of these! Though this diversity frustrates plant taxonomists, the rest of us can enjoy it :)

It would be foolish to try to cover the full range of Rosaceous fruit diversity. Readers would begin to fall away less than halfway through. Instead here are some favorites, starting with complicated and delicious types, and finishing with one that's quite simple and not at all tasty, but spectacular in its own way.

But first ... do you know which Rosaceous fruit type is most widely consumed by humans?

Our favorite fruit in the Rose Family is a pome, from Old French "pome" meaning apple (source).

Malus domesticus, the domestic apple tree, probably originated in the mountains of Central Asia. Now it's represented by thousands of cultivars grown in temperate regions worldwide. The apple itself is a pome, which botanists define as a fruit with "a central core containing multiple small seeds, which is enveloped by a tough membrane and surrounded by an edible layer of flesh." Technically speaking, the thick fleshy layer is an accessory structure.

Slicing an apple in half lengthwise shows how evolution elaborated on the basic seeds-in-mature-ovary structure in creating the pome.

Granny Smith apples. Photo by benjamint444, labels added.

The pome is unique to the Rose Family, but not just to apples. Pears and quinces also bear pomes, as do many native species. Their pomes are small, but look closely—they are indeed tiny apples.

Pomes of four species of hawthorne (Crataegus), c. 1 cm diameter; by Nadiatalent.

Another popular fruit type with a delicious accessory structure is the drupe, also known as stone fruit.

Domestic cherry—one of many delicious drupes in the Rose Family (source unknown). 

The genus Prunus includes what appears to be a diversity of fruits: cherries, plums, peaches, nectarines, apricots, and almonds! But in fact they all are drupes, defined as "fruit in which an outer fleshy part surrounds a single shell (the pit or stone) with a seed (kernel) inside" (source). [Unlike pomes, drupes are not limited to the Rose Family. For example, olives and dates are drupes.]

A sliced peach reveals tasty flesh surrounding the pit. DG Passmore, 1895, National Agricultural Library.

The almond tree, Prunus dulcis, also bears drupes. The almond itself is a seed (source; labels added).

Drupes are well represented in the wild, for example our many species of wild cherries.

Harvest time! Chokecherries, Prunus virginiana, by Matt Lavin.

"Thousands of drupes readied to make chokecherry whatever" says Matt. Would that be jelly? wine?

Now we advance to a higher level of complexity—a fruit that develops from multiple ovaries of a single flower. A tasty but controversial example is the strawberry (actually not a berry but that's not the controversy).

Wood Strawberry, Fragaria vesca (Jakob Sturm, 1798, BHL via Flickr). Question added.

Strawberry flowers are typical of the Rose Family (see above). But after fertilization, things get interesting. The many ovaries, each containing a single ovule, mature to become achenes—dry one-seeded fruits (g/G in illustration). At the same time the flower base (receptacle) grows, becoming a red mass of yummy flesh with the achenes embedded on its surface (f in illustration).

Herein lies the controversy: What is the fruit of the strawberry? Is it the fleshy globe adorned with achenes, or the achenes themselves? Some botanists rage over this, insisting achenes are the true fruits (in Wikipedia for example). Others think this silly, and simply refer to strawberries as aggregate fruits (my preference).

Young strawberry, with styles still present on maturing achenes (Olivier via Flickr).

Wild Strawberry, Fragaria virginiana (JW Frank via Flickr).

As promised, the final fruit is simple but beautiful—a single achene, specifically that of Mountain Mahogany (genus Cercocarpus). These shrubs and small trees of the arid American West are members of the Rose Family. But no matter how long one stares at their little flowers, it's hard to see roses.

Flowers of Birchleaf Mountain Mahogany (C. betulifolia) are just 5 mm across and have NO petals. The sepals form a cup with many stamens surrounding a single pistil (Joe Decruyenaere via Flickr).

A Mountain Mahogany flower may be humble, but not the resulting fruit. The pistil and its ovule become an achene with a long persistent feathery style, ready to fly with the wind. En masse, these "seed tails" transform the plant that bears them.

Fruits of Mountain Mahogany (C. montanus) preparing to launch; seed tails to 8 cm long (Matt Lavin).

Mountain Mahogany transformed by seed tails. Achenes can be spectacular! (C. ledifolius, Matt Lavin)

Now we return to where we started—"How many Rosaceous fruits are in Roesen's painting?" The answer is "many" (exact number depends on your opinion regarding aggregate fruits). I found pomes (apples), drupes (peaches, plums, cherries, maybe nectarines), aggregates of drupes (blackberries), and aggregates of achenes (strawberries). Did I miss anything?

This has been quite a long post, I agree. But I would be remiss if I were to omit Robert Frost's thoughts on the subject.

Sources (in addition to links in post)

Rosaceae in Flora of North America, which includes a list of fruit types:

"... achenes aggregated or not, follicles aggregated or not, drupes aggregated or not, aggregated nutlets, pomes, aggregated drupelets, or capsules; sometimes involving accessory organs, for example, hypanthium, torus."

Haywood, VH. 1978. Flowering Plants of the World. Oxford University Press.

Judd, WS, et al. 2002. Plant Systematics, 2nd ed. Sinauer Associates, Inc.

South Dakota Tree-Following—Plains Cottonwood

"A circle of cottonwood-leaf toy tipis made by Indian children of Plains tribes ... These they made in numbers and placed them in circles like the camp circle of their tribe." (Gilmore 1919)

Last month I launched a project to get to know the trees of South Dakota, starting with Black Hills Spruce, the state tree. This month I chose Plains Cottonwood, which was a strong state-tree competitor and rightfully so. Plains Indians relied on it for construction materials, fuel for heat, and winter food for horses. Fur traders built stockades and boats from cottonwood trunks. And as early travelers slowly made their way across the prairies, the occasional tree offered a welcome bit of shade. That hasn't changed.

Plains Cottonwood, western South Dakota. I ate lunch in its shade every day during a grassland project.

While looking for information, I came across a thought-provoking article: "Cottonwood Houses, Cottonwood Stars" (2014). Much of it is included here. Sometimes a look back shows what has happened since. Sometimes we can undo a bit of that.

In the early 1900s, ethnobotanist Melvin Gilmore visited with elderly Indians of the Great Plains, specifically those who had gathered native plants and still knew the old names and uses. He hoped to record this knowledge "while it may still be obtained, before the death of all the old people who alone possess it.” As it turned out, those old people were eager to share so that “future generations of their own people as well as the white people may know and understand their manner of life."

Gilbert observed and described construction of toy tipis from the broad deltoid leaves of Plains Cottonwood, Populus deltoides ssp. occidentalis. Ten years ago, I carefully followed his instructions:

"They split a leaf a short distance down from the tip along the midrib; at equal distances from the tip they tore across from the margin slightly; then, bending back the margin above the rents for the smoke flaps, and drawing together the leaf-margins below the rents and fastening them with a splinter or a thorn, they had a toy tipi."

Smoke flaps regulate draft and ventilate the tipi, especially smoke from the fire.

My camp circle.

Another gift of the Cottonwood are the stars concealed in its twigs. Kathleen Cain learned this as a child in rural Nebraska, from her father.

"You have to find [a twig] with a sturdy knuckle ... You have to cut cleanly ... One cut is best ... He turned the twig so I could gaze directly into its center. Running crosswise through the middle of the small piece of wood, the cut revealed a reddish-brown and nearly perfect five-pointed star." (Cain 2007)

A sturdy knuckle—the joint between two years’ growth. If you want to look for a cottonwood star, other species will work also. This is P. acuminata.

This cottonwood star is 6 mm across.

As I learned from my cottonwood projects, being a child again is therapeutic. As if to drive the point home, this showed up in The New York Times today:

"If I had influence with the good fairy who is supposed to preside over the christening of all children, I should ask that her gift to each child in the world be a sense of wonder so indestructible that it would last throughout life, as an unfailing antidote against the boredom and disenchantments of later years, the sterile preoccupation with things that are artificial, the alienation from the sources of our strength." Rachel Carson, The Sense of Wonder

Sources

Cain, K. 2007. The cottonwood tree; an American champion. Boulder, CO: Johnson Books.

Cottonwood Houses, Cottonwood Stars. November 2014.

Gilmore, MR. 1919. Use of plants by the Indians of the Missouri River region. Bureau of American Ethnology.

Johnson, W. Carter, and Knight, Dennis H. 2022. Ecology of Dakota Landscapes; past, present, and future. Yale University Press (in print and ebook format).

This is my report for the February gathering of tree followers, kindly hosted by The Squirrelbasket. If you'd like to join us, you can learn more here.

Scaling a Dome of Broken Glass

View south from top of Obsidian Dome; Glass Creek Dome mid photo, Sierra Nevada on skyline.

After touring the Mono Craters, accompanied by the spirit of pioneering geologist Israel Russell, I drove south on US 395 to see more of eastern California's volcanics. This time I was led by Robert P. Sharp and Allen F. Glazner, authors of Geology Underfoot in Death Valley and Owens Valley (1997, first edition).

I was intent on visiting a rhyolite dome or coulée (lava flow), landforms that had puzzled Russell during his fieldwork in the Mono Basin in 1883. "These outbursts of acidic lava are in strong contrast with the overflows of basic rock with which geologists are most familiar ... [which] are frequently quite liquid at first, flow rapidly, and reach a distance of many miles before congealing sufficiently to check their progress." Not so the Mono coulées. They barely reached beyond the foot of their cones.

Mono Craters, added arrows point to coulées—short thick lava flows with rugged surfaces and steep sides (from USGS 1971).

Russell rightly concluded the lava had been extremely viscous and therefore flowed very slowly. He considered these coulées unusual, perhaps unique. Surely geologists would be eager to study them. "When the valley in which these craters are situated becomes more familiar to tourists and geologists, they can not fail to be widely known as typical illustrations of mountains formed of acidic lavas." And so it came to pass.

Time has proven Russell wrong in thinking the Mono coulées unique; similar flows have been found around the world. But he was spot on about geological interest. Rhyolite volcanoes are relatively uncommon, so their abundance in eastern California makes the area attractive to volcanologists. Especially intriguing is their youth. Most erupted in the last 10,000 years, several in the last thousand. And they may be only sleeping.

Between Mammoth Mountain and Mono Lake "virtually every hill is a young volcano" (Sharp & Glazner 1997; NASA photo 2000).

Rhyolite domes and coulées are not easy to examine, as Russell explained. "The extreme ruggedness of the coulées is due to the fact that they hardened at the surface during the time they were still moving. The crust thus formed became broken and involved in the pasty material beneath in a most complicated manner. ... Even at the present day, after many blocks have fallen and the formation of a talus slope has commenced, the climber finds it extremely difficult to scale these rugged and broken escarpments of glassy fragments."

Flow front, North Coulée, Mono Craters.

However not far from Mono Craters is a dome that can be scaled without difficulty. On the west side of Obsidian Dome a road ascends the rugged broken escarpment to the top. A locked gate limits access to all but foot traffic.

The Obsidian Dome volcano erupted in 1350, just 633.5 years ago (associated tree mortality occurred in late summer of that year). Lava slowly oozed from the vent and flowed outward, forming what looks like a giant cowpie 1–2 km across and 50–100 m thick, its surface rough with jumbled blocks of volcanic rock. Aside from its shape, Obsidian Dome is similar to the Mono Crater coulées that Russell found so striking with their steep sides and rough surfaces. "Obsidian Coulée" is actually more appropriate.

Obsidian Dome, the cowpie coulée. Google Earth 2019.

Looking ± northeast at Obsidian Dome; blue line is gated access road. Gray area is an old pumice quarry, the reason for the road. Google Earth 2019.

Obsidian Dome and its road are featured in the geological vignette "Ominous Ooze" in the first edition of Sharp and Glazner's guide. I like the first edition very much. It provides more detail in descriptions and discussions, for example nine pages are devoted to Obsidian Dome vs. only three in the second edition. I found it especially helpful in appreciating the varied and beautiful rocks on display—all rhyolite and yet so different!

Formidable slope of broken glass, slightly worried field assistant for scale.

But the ascent turned out to be a stroll :)

Chunks of black glass were beautiful to the eye but challenging for the camera's light meter.

"Glass" and "glassy" often appear in descriptions of rhyolite volcanoes. Accustomed as we are to the transparent stuff, this can be confusing. Broadly speaking a glass is a non-crystalline solid that cooled so quickly from a liquid state that crystallization was impossible. A myth persists that glass is actually a super viscous liquid that flows at the scale of centuries (for example in old window panes). This has been discounted. But the transition of glass from liquid to solid remains an unsolved problem in physics.

Whatever the exact nature of glass, the volcanoes that extruded these domes and coulées were well equipped to produce it. The magma was >70% silica; at such a high concentration silica tetrahedra (molecules) bind tightly to each other, making super viscous lava. Not only did it barely flow, it was so viscous that other kinds of atoms couldn't move around and bond with their brethren to form crystals. When crystal-poor lava such as this cools rapidly, for example by being carried to the surface in a volcanic eruption, obsidian and other forms of volcanic glass result.

The tiny silica tetrahedron plays a big role in volcanoes (source).

Obsidian with scattered small crystals in a matrix of glass.

At the base of the coulée and along the road to the top I saw lots of obsidian with bands of pale pumice—also a glass but filled with bubbles. Perhaps it formed from frothy lava during a more explosive phase. These rocks were especially beautiful with their varied combinations of banding, curves, and swirls.

What happened here?!

Amid the shiny black broken glass, and sometimes bonded to it, was dull pinkish orange and gray rock that seemed out of place. It turned out to be one of the more interesting finds of the day—stony rhyolite, which has the same chemical composition as obsidian but is crystalline. Even more intriguing, given enough time obsidian will become stony rhyolite.

Those atoms that initially were stymied in their attempts at crystal formation don't give up! It may take a million years but eventually they find a way through the silica tetrahedra, meet their brethren, form crystals, and convert the non-crystalline obsidian to stony rhyolite.

Stony rhyolite can be as beautiful as obsidian.

But why is there stony rhyolite on Obsidian Dome, which erupted just 633.5 years ago? The explanation may be water. Water vapor can facilitate crystallization by breaking bonds in the silica tetrahedra, making the lava less viscous. Perhaps some of the magma contained enough water vapor to produce stony rhyolite right away (Sharp & Glazner 1997).

The hike wasn't long, but there was so much to see! Finally we reached the top. The landscapes were surreal.

Coarsely vesicular obsidian, part of a squeeze-up (read more here).

Sharp and Glazner end their vignette with the difficult but unavoidable question—why are these volcanoes here? Volcanologists have made some progress in answering it. They've even drilled deep into Obsidian Dome, thanks to the road to the old pumice quarry. But that's the subject of a future post, after our next visit.

The Inyo Dike, suspected source of Obsidian Dome and its neighbors (Reches & Fink 1988).

Sources

Fisher, RV, Heiken, G, Hulen, JB. 1997. Volcanoes: crucibles of change. Princeton U Press.

Reches, Z., and Fink, J.H., 1988, The mechanism of intrusion of the Inyo dike, Long Valley caldera, California: J. Geoph. Res. 93:4321–4334. https://doi.org/10.1029/JB093iB05p04321

Russell, IC. 1889. Quaternary History of Mono Valley, California in USGS 8th annual report (If the USGS PDF is slow to load and read online, try HathiTrust.) Russell's report was printed separately in 1984 by Artemisia Press, Lee Vining, CA (out of print).

Sharp, RP, and Glazner, AF. 1997 (4th printing 2003). Geology Underfoot in Death Valley and Owens Valley. Mountain Press. NOTE: A revised second edition was published in 2022 (Glazner, Sylvester, & Sharp). Based on the areas I've visited, it seems more science light. But of course maps and illustrations are far better. Perhaps buy both.

Vogel, TA, et al. 1989. Petrology and emplacement dynamics of intrusive and extrusive rhyolites of Obsidian Dome, Inyo craters volcanic chain, eastern California: J. Geoph. Res. 94:17,937–17,956. PDF (Open Access)