Michael Dosmann and Elizabeth Thomas collect rare plants in the places of their discovery.
We met Gerry Wilhelm on that late-September morning last year at the side of a tree-lined road within the Jurgensen Woods Nature Preserve. Surrounded by a network of residential communities, commercial development, and highway corridors, this site in Cook County, just south of Chicago, was a bastion for nature and nature lovers alike. Donned in a light blue button-down and a many-pocketed tan vest, the bespectacled Gerry greeted us with a broad smile. As we stepped into the nearby remnant sand prairie ringed by black oaks and sassafras, we knew we were about to experience something special. At that time of year, much of the herbaceous vegetation looked a bit drab and tired, the verdant greens of summer waning to olive; late blooming goldenrods and asters complemented the tawny-brown grasses. And yet, dotted around the landscape were these rounded shrubs, about a meter in height and as wide or wider, and covered with glossy, deep green, oblong leaves. This was the muse for the day: Hypericum swinkianum, something that neither of us had seen before.
In 2016, while working on the Flora of the Chicago Region: A Floristic and Ecological Synthesis, Gerry and his co-author, Laura Rericha-Anchor, published H. swinkianum as a new species of St. Johnswort. The name commemorates the late Floyd Swink, botanist at the Morton Arboretum, expert on the region’s flora, and mentor to them both. While it was like Hypericum kalmianum, another Midwestern native, this one is characterized by larger leaves (up to 5 cm long and 1 cm wide), more numerous flowers in a cluster, and a preference for acidic soils (H. kalmianum, in contrast, adores a higher soil pH). The following day, we visited several populations of Kalm St. Johnswort, and in contrasting the two even further, Swink’s just had a juicier look to it, its sleek, dark leaves looking plastic-like. Perhaps the robust look had more to do with the local conditions at the population, or maybe there is something baked within? It isn’t every day you visit a species’ type locality, much less with a person who named it. Where we stood that day in Jurgensen Woods happened to be Swink St. Johnswort’s. This means that it was the very spot from which its type specimen was collected. When botanists describe a new-to-science species, they assign it a unique name in Latin, and publish a description of its traits that allows others to distinguish it from other species. They also designate a type herbarium specimen—a dried and pressed cutting from the plant stuck to stiff paper—that in the botanists’ minds best illustrates those important diagnostic features. Types are revered in herbaria, where they are filed in special cherry-red folders and serve as physical reference forever as to what a scientist hypothesized the species to represent. In other words, it is the “real deal.”
While there is great value in preserving and studying those dead plants, there is equal value growing them in an arboretum. No matter how well preserved those flowers are, the color of the petals fades in time. There is also only so much vegetation that you can fit on a sheet of paper roughly 30 cm by 40 cm in size—it is impossible to properly capture the grandeur of an oak or the “juiciness” of this St. Johnswort. As we gathered our seeds from this population and yes, accompanying herbarium and DNA vouchers, too), we were eager to be the first ever to introduce this species into cultivation at the Arnold and Polly Hill Arboreta, as well as a few other botanical gardens. Not only will those living specimens serve as valued conservation collections, but they also provide ample opportunities for scholars to study, observe, and enjoy them without pressuring the plants in nature. And, like the type specimen in an herbarium, these from the type locality—collected with one of the species’ authors, no less—also represents the “real deal!”
Growing plants ex situ in the garden also provides a chance to evaluate a plant species’ horticultural value and plasticity. Some plants in the shrub border, exuberant in their display, didn’t start out that way. Some are the result of artificial selection via breeding, others are clones of a plant (wild or cultivated) that happened to possess superior traits (larger flowers, uncanny fruit color, variegated leaves). There are also those plants that simply benefit (from an ornamental perspective) from management—siting them under ideal conditions (no competition, just the right amount of water and light), giving them a gardener’s care (primping, pruning, being spoken to). Looking at those gorgeous plants that day, we could not help but wonder aloud “If they look this great here, what happens when you give them some horticulture?”
Almost every shrub in Jurgensen Woods that day was a mass of vertical, slender stems arising from the base. In a way, the habit was akin to a Daphne or a Genista. The oldest stems in the middle stood just a bit taller than the rest and possessed a few lateral branches; these also had exfoliating, gray-brown bark. Few of the shrubs seemed more than several years old, making us wonder if they are naturally short-lived. Would the centers eventually die out, leaving a green donut? If so, can they be rejuvenated like other shrubs?
If they look this great here, what happens when you give them some horticulture?
For many summer-flowering shrubs like Hypericum, which bloom on new wood, a late-winter or early-spring cut-back can create a compact and densely flowered specimen. Fruiting was heavy on the plants we saw, making it very easy to yield the required seed counts. Pretty much every stem ended in a branched or compound dichasium, a cluster of symmetrically and oppositely paired fruits, some bearing upwards of 30 yellowish-green, fleshy capsules; a few were even turning coral red. The blooming shrub masses must have been a sight to see earlier in the summer. Each flower bears five bright yellow petals about 1.5 cm long that surround a pack of too-many-to-count yellowish stamens. Imagine them juxtaposed against the shiny, blue-green leaves, covering shrubs in a mixed perennial and shrub border.
Of course, it remains to be seen just how amenable to cultivation Hypericum swinkianum ends up being. Many a plant, dazzling in nature, evades successful cultivation in anything other than niche garden spaces. (Referring to Franklinia alatamaha once in these pages, Peter Del Tredici aptly described such plants as “miffy.”) Will this St. Johnswort be similar, resisting cultivated love and requiring the wet, acidic soils reminiscent of the mesic sand prairies it once called home? Or, will they grow–thrive—in drier sites, where the pH is higher and gardeners put them through a range of horticultural calisthenics?
Many a plant, dazzling in nature, evades successful cultivation.
We pondered these questions while slicing open the yellowish-green ovaries with our thumbnails. Although not yet fully ripened into the dry, brown, dehiscing capsules characteristic of mature Hypericum fruits, they revealed masses of granular, chocolatey, well-developed seeds inside. Confident they were far enough along to continue ripening off the plant, we fanned across the prairie patch to capture the greatest genetic diversity we could from this persistent population, funneling fistfuls of the ripest fruits into hand-sized glassine seed envelopes, perfect for their non-stick and waterproof properties.
Sometimes, the vagaries of seasons and schedules can find you schlepping to a site only to meet a plant at its phenological margin. This was indeed a trip of margins, and type localities: just the day before, we’d collected the mature “cones” of another rare plant, Betula murrayana, also from the exact location—and individual plant!— from which it was originally described. Well into its seed dispersal period, we managed to snag a few of the last-remaining fruits of North America’s rarest birch before they were lost to the wind. Visiting two type localities within a three-day collecting trip, and finding both ripe for collection? Yeah, we were lucky.
Walking back to our vehicles with an abundance of seed and a swarm of angry ground hornets at our heels, we continued to muse over the horticultural potential of Swink’s St. Johnswort. Could it become the next “must have” summer-blooming shrub for the pollinator garden? And so far, this new species is known to occur only in northern Illinois and Indiana, as well as western Michigan—primarily in the vicinity of Lake Michigan. Will additional populations be discovered?
Time will tell.
Michael S. Dosmann is the keeper of living collections at the Arnold Arboretum. Elizabeth Thomas is a research associate at Polly Hill Arboretum.
From “free” to “friend”…
Established in 1911 as the Bulletin of Popular Information, Arnoldia has long been a definitive forum for conversations about temperate woody plants and their landscapes. In 2022, we rolled out a new vision for the magazine as a vigorous forum for tales of plant exploration, behind-the-scenes glimpses of botanical research, and deep dives into the history of gardens, landscapes, and science. The new Arnoldia includes poetry, visual art, and literary essays, following the human imagination wherever it entangles with trees.
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