Why Trillium Have Become the Poster Child for Endangered Native Plants

That good things come in threes was a lesson I learned in stages. It began years ago, when I bought my house in the Hudson Valley and noticed three tiny plants growing under the edge of the front porch.

I did not know it then, but they were trilliums — specifically, the native wake robin of the surrounding woodlands, also known as Trillium erectum. I lifted the anonymous creatures out with a trowel and moved them to a bed I was making, just in case they were “something.”

They were something, indeed. And now many of these ephemeral spring plants bloom around my May garden, all of them descended from those first three.

Most of the trillium learning I have accumulated along the way has felt tinged with serendipity or a kind of magic, like that first time. But not the latest installment, from a report published in April that analyzed the risk factors to North American trillium in the wild.

The report revealed that 32 percent of our native trillium species or varieties are threatened with extinction, thanks to human development, predation by white-tailed deer and feral hogs, competition from invasive plants and more.

Trillium erectum, also known as the wake robin, red trillium or stinking Benjamin, holds its flowers above its green leaves on short stalks called pedicels.Credit…Margaret Roach

The plight of any native species is cause for concern, but with trillium there is another layer — almost an emotional factor. Their distinctive, early flowers charm us, making them a kind of poster plant for other species in trouble, ambassadors for an interest in growing and conserving natives. Botanists often refer to them as “charismatic” flora.

Trillium speak to people.

“Any organism that can galvanize the public — we need more of those,” said Wesley Knapp, chief botanist for NatureServe in Arlington, Va., one of three conservation nonprofits behind “The Conservation Status of Trillium in North America,” the 86-page report. “We don’t have many communication tools like that.”

The status of trilliums in the wild was assessed in partnership with the New Mexico BioPark Society and Mt. Cuba Center, the native plant garden and research facility in Delaware. The study’s genesis: The International Union for Conservation of Nature’s medicinal group had funding to evaluate the state of trillium, a genus used in traditional medicine. They approached the BioPark Society, which reached out to Mt. Cuba, which in turn involved NatureServe, whose database, populated by member programs across the U.S. and Canada, is a tool frequently used to assess the status of plants.

The three teams gathered with other North American experts for four days in October 2019, “to pore over maps, published information and personal observations from the field,” said Amy Highland, the director of collections and conservation lead at Mt. Cuba, which hosted the meeting.

Trillium cernuum, the nodding trillium, a Northern species. Trillium parts come in threes, including flowers with three petals and three sepals beneath an enclosed, unopened bud. The leaves on mature plants usually come in threes, too.Credit…Mt. Cuba Center

Three-Part Harmonies

The Latin expression behind the idea that good things come in threes — omne trium perfectum — could have been coined for trillium.

As the plant’s prefix suggests, trillium parts come in threes: The flowers typically have three petals. Three sepals beneath the petals fit together to enclose the unopened bud. And what we call the leaves (technically bracts) usually come in threes, too, on mature plants.

Trillium number about 50 species globally, most of them in North America. Their three areas of concentration — there’s that number again — are the eastern half of North America, the Pacific Northwest and Eastern Asia. The greatest diversity is in the American Southeast.

Structurally, trilliums fit into two primary groups. Some are pedicellate — like my red ones and other Northeastern species — holding their flowers above the leaves on a short stalk, or pedicel. Others are sessile, with the flowers sitting directly on top of the leaves. Leaves mottled with splashes of silver or purple are a feature of some sessile types, including various Southeastern species, making them extra-choice to a gardener’s eye.

Trillium cuneatum, the toad trillium or little sweet Betsy, is a sessile type, with flowers sitting directly on top of the leaves, rather than held on stalks.Credit…Mount Cuba Center

“Lush wildflower displays with trillium as one element” is how Mr. Knapp describes the spring shows in the cove forests of the Great Smoky Mountains. They might include companions like blue cohosh (Caulophyllum thalictroides), columbine (Aquilegia canadensis) and broad-leaved toothwort (Cardamine diphylla).

“In the Eastern U.S., trillium are forest-dwelling species,” he said. “But the types of forests can be strikingly different, from rich cove forests of the Southern Appalachians to Atlantic coastal forests with more acidic, swampy soil.”

When botanizing, Ms. Highland might find them with other species that can inspire shade-garden combinations, like woodland phlox (Phlox divaricata), bloodroot (Sanguinaria canadensis), Virginia bluebells (Mertensia virginica) or false Solomon’s seal (Maianthemum racemosum). In Mt. Cuba’s gardens, masses grow among ferns, foamflower (Tiarella cordifolia), wild ginger (Asarum canadense) and more.

Trillium like the yellow-flowered T. luteum make good shade-garden companions for other native woodland wildflowers like foamflower (Tiarella cordifolia) and creeping Phlox (P. stolonifera).Credit…Mt. Cuba Center

Making More Trillium: Of Ants and Plants

I have watched as my trilliums’ offspring have expanded their territory over the years, sprouting up in the oddest spots and patterns. One group has arranged itself almost in a circle.

I have many generations of ants to thank, apparently, as they are participants in a form of plant-animal mutualism called myrmecochory. Attracted by an elaiosome, a lipid-rich packet attached to the trillium seed, the ant carries the whole thing back to its nest, feeding the elaiosome to its larvae and then discarding the seed.

That rich soil environment in and around ant nests is apparently favorable for trillium germination. Also, it is an advantage for a plant to have its seed sown some distance away from the parent: In case something happens to the original plant, there is a backup.

This form of seed dispersal is common to many native woodlanders, including violets, bloodroot, squirrel corn (Dicentra canadensis) and Dutchman’s breeches (D. cucullaria). Ants may not exactly be garden designers: I now have trillium and other myrmecochorous species growing in some very odd spots, because an ant decided to drop a seed there. But they are impressive ecosystem engineers.

“The first time I saw a trillium ring, I was very confused, as a scientist,” Mr. Knapp said. “And then I saw it a couple of more times and learned what it was.”

“You feel like you’ve stumbled across some kind of fairy magic,” Ms. Highland said. “Like, who put that circle there?”

When I intentionally move trilliums to a new spot, it isn’t by seed but by digging and dividing at flowering time, when the plants are easy to see. I dig just beyond the perimeter of a clump to lift it, and then tease or sometimes cut apart the knobby underground rhizomes, insuring that each division has at least one growing point.

A clump of Trillium erectum dug from a garden bed at flowering time to divide and move. Dig just beyond the clump’s perimeter to lift it, and then tease or cut apart the underground rhizomes, insuring that each division has at least one growing point.Credit…Margaret Roach

Trilliums in Trouble

The threats to trillium outlined in the report by Clayton Meredith, New Mexico BioPark Society’s species survival officer for plants, include human development. But predation by white-tailed deer and habitat damage by feral hogs threaten more types of trillium than anything else.

As tough as trilliums’ underground rhizomes are, that toughness goes only so far in the face of repeated browsing by white-tailed deer. When the blooms are removed, it means no seed will be set. The trillium reproduction cycle, from seed to flowering plant, takes four to seven years — a remarkably long time for herbaceous plants, Mr. Knapp said — so a lost year is costly.

Rooting by feral hogs can destroy not just the plants they upend, but the habitat, too. The animals — a hybrid of the Russian boars introduced to the South a century ago for hunting and domestic hogs escaped from farms — are gradually expanding their range, Mr. Meredith writes, moving northward and westward.

And then there are the competing plant species. Those he cites as most likely to continue displacing trillium are Chinese privet (Ligustrum sinense), bush honeysuckle (Lonicera maackii) and garlic mustard (Alliaria petiolata), “each of which forms dense stands which impede successional stages and directly impact herbaceous understory species.” The likes of burning bush (Euonymus alatus), English ivy (Hedera helix) and Japanese stiltgrass (Microstegium vimineum) are on the list, too.

In the Northwest, Himalayan blackberry (Rubus armeniacus) is the primary invasive plant culprit. But the increasingly common wildfires there caused by climate change are pressuring trillium populations, too.

The flowers of the great white trillium, T. grandiflorum, may fade to pink as they age, but some more unusual individuals start out that way, blooming in a distinctive rose-purple color.Credit…Mt. Cuba Center

A Storehouse of Genetics

The collection of wild plants for medicinal or horticultural purposes is another threat, but one that is harder to assess.

To avoid supporting poaching, gardeners should buy only plants that have been nursery propagated. Before buying, ask where the plants came from.

All of these factors highlight the importance of ex situ, or off-site, conservation — like the collection of 84 types of trillium that Mt. Cuba maintains, including genetic material “meant to live here until it’s needed back out in the wild, when we can propagate it and put it back,” Ms. Highland said.

The plight of trillium makes Mr. Knapp reflect on another group of charismatic plants, native orchids.

“When I was getting started, I remember seeing some wild orchids — a transformative moment for a young botanist,” he said. But by then, orchids were far less common than they had been a mere generation before.

“Maybe I wasn’t interested in them as much, because I wasn’t seeing hundreds at a site as I might have 20 years earlier,” he said. “And now I keep thinking: Will the next generation of botanists not be enamored with trillium because they may never see masses of them?”

Margaret Roach is the creator of the website and podcast A Way to Garden, and a book of the same name.

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