The Mystery Tree Found in Autumn Hill Reservation

Not everyone gets to discover and report on a new invasive species in one's adopted home town. Though there were a couple kinds of invasive plants that I caught early enough to hopefully keep from spreading through town--thorny mile-a-minute and more recently the dreaded common buckthorn--this particular discovery is different, in that people have yet to agree on what it is. How strange it can feel, in a time when the internet can instantly tell you everything about everything, to find a plant to which no one can with certainty give a name.

I first encountered a single specimen of the mystery tree while conducting a plant inventory in Roger's Refuge in 2007. Only in the past few years have I found it proliferating in Herrontown Woods and Autumn Hill Reservation. 

Some call it a shrub, though when it grows to 30 feet, maybe it's time we start calling it a tree. There's agreement that it is in the genus Pourthiaea--a name that people will struggle to spell and pronounce (my attempt at a pronunciation is "pore-THEE-uh"). In a discussion on iNaturalist, the citizen science site for reporting and identifying species, some try to call it asian photinia (Pourthiaea villosa)--a nonnative shrub that likely escaped from Princeton-based nurseries long ago.

They are surely wrong, as the leaf shape and fall color of asian photinia are clearly distinct. This bright golden yellow is increasingly prettifying and clogging Princeton's greenspaces, from the Institute Woods in the west to Autumn Hill in the east, creating dense, exclusionary stands as it spreads beyond Princeton to proliferate across New Jersey. 

John L. Clark, a Princeton-based botanist frequently posting on instagram from the forests of Equador, has done a great deal of research into our mystery tree. Since the Pourthiaea genus originated in China, John tracked down a couple Chinese botanists to seek their insights. 

One, D.Y. Hong, responded that he was too old to take on the challenge of identifying the tree.

Another, Bin-Bin Liu, was also apparently unable to assist. John laments that botanists now trained in phylogenomics can identify gene sequences but not the actual physical plants themselves. 

There have been various species names thrown at the mystery tree--lurida, lucida, arguta--but none clearly stick thus far. Through Mike Van Clef, I learned of Jean Epiphan, a northern NJ plant expert at Rutgers, who had arrived at the species name "parvifolia", and even came up with a common name, "littleleaf photinia." Originally introduced in 1908 at the Arnold Arboretum," it's popping up in Morris County and, according to Jean, matches our mystery tree in Princeton. She has not seen it being sold in nurseries, and speculates that it is spreading from specimens in old estates. She sent a couple links (here and here) with descriptions, and a mention of it in Dirr's encyclopedic Manual of Landscape Plants.

Some sticking points, though, are that the link she sent to a photo has now gone dead, and the description is of a shrub less than ten feet high. A photo sent by Pat Coleman from Bowman's Hill Wildflower Preserve also matched our mystery tree in Princeton, but no word as yet whether they've come up with a name.

One thing to call the mystery tree is pretty, as are many invasive shrubs, both when they bloom and in the fall. This fall in particular, Autumn Hill Reservation was a jubilant jumble of colorful invasive shrubs, led by the bright red of winged euonymus, joined by the rich colorations of Linden viburnum and the golden yellows of the asian photinia Even the lowly privet got into the color game with an appealing dark bronze. 

When surrounded by such a dazzling visual display, it takes work to remind oneself that something important is being lost as these introduced species gain dominance in the understory. Their success and dominance is enabled in part through being rejected by deer, which prefer a diet of native plants. Thus, our eyes are well fed while the wildlife find themselves living in an increasingly inedible forest. 

As we lose many of the native trees dominating the canopy--chestnut, elm, ash, and now the beloved beech--the extra light reaching the understory drives the extravagant growth of nonnative shrubs. Surrounded by such a thorough invasion of nonnative growth, it is extraordinarily intimidating to contemplate the work involved to shift the balance back to the spicebush, blackhaw viburnums, blueberries, hollies, sumacs, and other natives currently getting smothered beneath the rising tide.

Native shrubs and trees don't exactly lack color. Here's a dogwood that was mixed in and easily confused with the mystery invasive. Note the way the leaves are paired rather than arising one at a time along the stem. 

All the invasive shrubs currently dominating were at one time, long ago, in a similar state, just starting to pop up here and there. Clearly there was no one back then able to see the future and take early action. In our era, the consequences of inaction are readily apparent. What is special about this moment in the history of Autumn Hill Reservation is that the mystery tree is still early enough in its invasion, and easy enough to spot in fall, that it can be stopped.  

Update:

Where found thus far:

• Rogers Refuge, Herrontown Woods, and Autumn Hill in Princeton
• Possible sighting in the Institute Woods in Princeton
• Bowman's Hill Wildflower Preserve
• Jockey Hollow and the NJ Brigade Area in Morris County
• Tourne Park, in Boonton

Update: A big thank you to "anonymous" in the comment section, who provided a species name and links to herbarium photos:

"Thanks for alerting us to this newly naturalized species. One of the best resources for documentation of plants on a global scale is GBIF. Reviewing the gallery of specimens online, the name leaves to appear to bear a resemblance to Photinia parviflora. https://www.gbif.org/occurrence/gallery?taxon_key=5363981"

Each photo at the link bears the name C.K. Schneid. Look at the wikipedia page for Camillo Karl Schneider and you'll find that he was a German botanist who traveled to China in 1913 to collect plants and seeds. His next stop was the Arnold Arboretum in Boston, where the species is said to have been introduced five years earlier by Wilson in 1908.

Each photo shows that the now accepted species name is not parvifolia but instead parviflora. 

Applied name Photinia parvifolia (Pritz.) C.K.Schneid.
Accepted name Pourthiaea parviflora (Cardot) Iketani & H.Ohashi

That puts into question the common name "little leaf photinia", since "parviflora" means little flower. 

So, we're not really there yet. 

Fall Colors Nature Walk, Sunday in Herrontown Woods

Early November, and it's time for a nature walk through the color-coded forest of Herrontown Woods. Color-coded because each tree and shrub is showing distinctive coloration that can make it a snap to identify, even from great distance. 

The walk will head out at 11am this Sunday, Nov. 2, from the gazebo at the Botanical Art Garden (Barden), next to the main parking lot, 600 Snowden Lane. The walk is free, but donations to the Friends of Herrontown Woods are welcomed.

Come early and enjoy coffee and baked treats at May's Pop-up Cafe in the Barden from 9-11, and with all the fall colors, take part in an art project called the Community Collage. 

Along with colorful leaves--still on branches or lying in a colorful collective on the ground--we'll see the bright berries of Hearts 'a Bustin'. If you look closely, you'll even see witch hazel in full bloom. 

Here are four native shrubs that have shown particularly bright fall color: blackhaw Viburnum ("blackhaw" means black berry),

a highbush blueberry along the Veblen House driveway,

winged sumac (a "volunteer" that popped up at the Barden),

and a particularly showy Hearts 'a Bustin' in my backyard.

Buckthorn--A New Highly Invasive Shrub Found in Princeton

For years, I've traveled between Michigan and New Jersey and noted how some invasive plant species that have run rampant in the eastern U.S. have yet to show up in the midwest. That is changing. Last year, I encountered a dramatic example of stiltgrass spreading down a hillside in Michigan, and there are reports of lesser celandine gaining a foothold there as well. Similarly, Princeton had remained free of the common buckthorn--the most invasive shrub clogging midwestern forests. That, too, is changing.

The fateful day came on September 16, 2025. I was standing in a spot I'd passed by many times, near the entrance to the Herrontown Woods parking lot, when I happened to look down and saw that characteristic leaf of common buckthorn--the first sighting, by me and perhaps anyone, of this uber-invasive shrub in Princeton. 

The leaves of common buckthorn (Rhamnus cathartica) have arc-shaped veins, and are described as "sub-opposite," because they can appear to be paired on the twig but are slightly staggered.

Buckthorn gets its name from the two terminal buds, which make the shape of a buck's hoof, with a thorn-like protrusion between them.

This photo from upstate NY shows there can be thornlike protrusions along the trunk as well.

Shunned by deer, buckthorn's combination of massive seed production and shade tolerance allow it to clog forests and bury whole native plant communities under its dense growth. The richly diverse bur oak savannas of the midwest were nearly lost beneath a rising sea of buckthorn. Only botanical sleuthing and the hard work of clearing buckthorn, honeysuckle and other invasive plants from beneath the massive oaks, along with reseeding and prescribed burning, has brought back that plant community. 

The small cluster of young shrubs I spotted at Herrontown Woods has fortunately not yet produced seeds. But anyone who has lived in the midwest knows the potential of buckthorn to grow, seed and spread.

An email to the Stewardship Roundtable group of land managers in NJ yielded some responses. Duke Farms has it, as does the Watchung Reservation. The Friends of Great Swamp have an info sheet on their website, so I suspect it has established itself there as well. Mike van Clef, who deals with invasive plants all across New Jersey, writes: 

Duke Farms definitely stands out! From iNaturalist, there are 64 research grade observations, heavier toward northern NJ but all over the state. I often find it as single immature individuals, especially in northern NJ...which is always a head scratcher because I never seem to find a nearby large fruiting individual...

This photo shows the lingering green of buckthorn in upstate NY. Like many invasive shrubs that evolved in a different climate, buckthorn keeps its leaves longer that native species in the fall. 

Given New Jersey's already long list of invasive shrubs clogging our forests--among them multiflora rose, Photinia, privet, and Linden Viburnum--it's hard to imagine another having much of an impact. Having seen what buckthorn does in other areas of the country, all I can say is "Watch out!"

Early detection and rapid response are key to stopping biological invasions. This is true both of the immune systems protecting our bodies and of land managers caring for nature preserves. At Herrontown Woods, we've done very well with that creed of early detection and rapid response. Lesser celandine and garlic mustard--the bane of many a nature preserve--are now vanishingly rare. Vigilance each year in August has helped keep many areas free of stiltgrass, the most rapid spreading of all. People who care and take action can make a difference.

On a town-wide scale, some early interventions have helped keep the thorny Mile a Minute vine from spreading across Princeton. Though Princeton has hired contractors to help counter at least some invasions in their early stages, it's hard to get private residents--often disconnected from the yards they own--to act collectively to knock out new invasive species before they become a problem. Having fought the good fight, my advice about buckthorn is: be informed, be on the look out, and be proactive. There's also a super handy, targeted, and frugal way for homeowners and professionals to cut and treat buckthorn and other invasive shrubs. Appropriately enough, it's called a Buckthorn Blaster. 

Seven Native Shrubs Offer a Progression of White Blooms in Spring

Why do gardens and nature diversify over time?  Since most flowers last only a week or two, any gardener seeking a steady progression of blooms will naturally seek out new additions to fill the gaps. This spring, I noticed a different sort of steady progression: of blooming trees and shrubs in nature's garden at Herrontown Woods. No gardener put this steady progression together.

Flowering dogwood (Cornus florida) put on a show in late April.

Blackhaw viburnums (Viburnum prunifolium) dotted the understory with white pompoms for the first few days of May, their period of bloom shortened by the heat.

Alternate-leaved dogwood (Cornus alternifolia) followed in the second week of May, with scattered blooms in the shade,

and abundant blooms in the sun.

Arrowwood Viburnum (Viburnum dentatum) in the lowlands sustained flowers through cool days in the second half of May, 

along with maple-leaved Viburnum (Viburnum acerifolium) up on the ridge.

In the last week of May, abundant disks of elderberry (Sambucus canadensis) flowers began an extended residency.

Still to come is silky dogwood (Cornus amomum), 

which will look remarkably like its predecessors when it blooms.

There are many examples of how native plants that have co-evolved behave in an egalitarian way. Though there are exceptions, they tend to "play well with others," sharing the ground rather than bullying their way to dominance. Might this sharing have a collective advantage that benefits them all?

People trying to understand why invasive species can be detrimental will rightly point out that many invasive plants provide abundant flowers for pollinators. But if one species comes to dominate, its week or two of blooms will be preceded and followed by precious few flowers, leaving pollinators little to sustain them through the season.

An interesting experiment would be to monitor what sorts of insects pollinate the progression of blooms generated by native dogwoods and Viburnums. Have their visually similar blooms evolved to attract the same sorts of pollinators? If so, they could be thought of as a sort of tag team, collectively sustaining the needed pollinators through the season. 

Native Fall Color and Berries in Herrontown Woods

One vision being gradually realized at Herrontown Woods through the power of incrementalism is the transformation of the long boardwalk into a native plant corridor that will be especially attractive in spring and fall. The boardwalk, given the V-ful nickname of Voulevarde because it was built by chainsaw virtuoso Victorino and leads from the main parking lot up to Veblen House, was intentionally routed past some mature examples of native shrubs.

Arrowwood Viburnum has toothed leaves (thus the latin name Viburnum dentatum) and can turn a brilliant reddish color in fall. 

We're managing the corridor for an open woodland, so that enough sunlight can reach the understory to power abundant berry making by the native shrubs. The many Blackhaw Viburnums, named after their black berries ("haw" means berry, as in hawthorn), are a dramatic example. 

The preserve's largest winterberry shrub--a holly called Ilex verticillata--greets you along a bend in the Voulevarde with abundant red berries this time of year.  

One of the preserve's large highbush blueberry bushes--they tend to be loners persisting here and there in the preserve--also grows along the route, with bright orange fall color.

The largest native swamp rose (Rosa palustris) in the preserve is also near the trail, its single pink flowers emanating a heavenly fragrance on hot summer days. Its rose hips are bigger than those of the nonnative multiflora rose. While the invasive multiflora rose is ubiquitous in the preserve, there are only two native swamp roses found thus far across 150 acres, mostly because the swamp rose needs more consistently wet conditions to compete. We've started planting more of them, in wet spots that get some sun, to see if we can increase their numbers over time. Again, the battle cry: "Incrementalism!"

Beyond the boardwalk, up towards Veblen House, is a good example of a rare native shrub, variously called Hearts a' Bustin' or strawberry bush. The deer love it so much that we needed to cage it until it was tall enough to escape their browsing. Located in a partial forest clearing, it receives enough sun to develop abundant berries.

In the fall, its leaves turn white. Hearts a' Bustin' is a native euonymus (Euonymus americanus), rarely seen due to deer browsing, while the nonnative euonymus, burning bush, is ubiquitous in the preserve and largely shunned by the deer. Notice a recurring story?

Up at the horserun near Veblen House, these look like shrubs or small trees, their fall color backlit by late afternoon sun. They are in fact trumpet vines growing on some sort of structure placed there decades ago. 

A different angle shows the trumpet vine with the bright red of Virginia creeper in the foreground. Both are native vines that can be a little aggressive, but sufficient shade deprives them of the energy to be obnoxious, allowing us to enjoy their best traits without any need to keep them in line.

Virginia creeper has five leaflets to poison ivy's three. These leaves look like they've donated some of themselves to the insect world. 

The boulders in Herrontown Woods, bedecked by mosses and lichens, are reminiscent of whales whose gray skin has collected barnacles. Sweetgum leaves are particularly creative and varied with their fall color.

Also generous with fall color is the native winged sumac, which has started to pop up in areas where we remove invasives. They seem to be part of the soil's memory of past eras when the forest was younger, before the canopy closed and shrouded the ground in deep shade. 

Another source of beauty, noticed while removing dead ash trees near the Veblen House driveway, is the combination of the old evergreen cedar trees with the deep burgundy of young white oaks rising to ultimately fill the space left by the ash.

The loss of ash trees to the emerald ash borer is a profound tragedy, but if we can take advantage of the new openings in the canopy to reawaken a diversity of native shrubs and trees, there is at least some recompense. 

Evolved Coexistence in Nature

What is "natural" in nature? I remember a 1990 column entitled "Bug Wars," in which NY Times columnist Anna Quindlin wrote about the gypsy moths that, back then, were defoliating vast areas of eastern forest. She used the destructive moths as fodder for reflections on nature and its ways, not knowing that the moths can hardly be thought of as natural. They were introduced from another continent, then escaped and multiplied, consuming forests that had not evolved any defenses against them. Fortunately, scientists found a very low-toxicity way to limit the gypsy moth's numbers, though sustaining that balance requires ongoing human vigilance and action.

With introduced insects and diseases having decimated first our ashes and now our beech trees, it's worth noting the more sustainable relationships between plants and animals that have co-evolved over millennia on the same continent. 

Tent Caterpillars and Black Cherry

This spring, tent caterpillars defoliated some of our black cherry trees. Were the caterpillars a threat to the trees? Well, they finally got their fill and wandered off to pupate and become moths, leaving the trees to sprout new leaves and grow unhindered for the rest of the summer. The trees may grow more slowly, but their survival (and therefore the survival of the tent caterpillars that depend upon them) is not in peril. 

 

Hibiscus Sawfly and Rose Mallow Hibiscus

Near the gazebo in the Barden at Herrontown Woods grows the local native hibiscus (H. moscheutos). Earlier this summer, its leaves were getting eaten. 

Some internet research suggests that these are larvae of the hibiscus sawfly. 

If the culprit had been an introduced insect, I might have worried. For instance, each year I see more evidence of our arrowwood Viburnums being eaten by the Viburnum leaf beetle, an insect introduced from Europe. Because the beetle's arrival is fairly recent, we don't know if it poses an existential threat to Viburnums.

But given that the native hibiscus sawfly has been interacting with the native hibiscus for thousands of years, that long track record of coexistence is reassuring.

 

Though many leaves were partially eaten, the hibiscus grew new ones that remained unaffected. I think of this relationship as akin to someone who donates a percentage of their income to good causes each year. 

An Aphid-like Insect and Hickory Trees

Earlier this year, some leaves of a young hickory tree developed these green bumps. They appear to be hickory leaf galls, caused by an aphid-like insect in the genus Phylloxera. 

The hickory leaves ultimately curled up. The insect's lifecycle sounds much like that of the introduced nematode that causes beech leaf disease. Should we be worried for the future of hickories?

Again, the aphid-like Phylloxera and the hickory tree "go way back," and through those millennia a balance seems to have been struck. Only the lower portions of the tree appear affected. The hickory continues to grow. 

Psyllids and Persimmon

Lastly, a twig on a native persimmon in Herrontown Woods was showing symptoms of contorted leaves similar to those proliferating on nearby beeches. Might we be losing our persimmons? Again, some internet research points not at apocalypse but at coexistence, between the native persimmon and a native insect called the persimmon psyllid. 

According to a NC State website,

"On native persimmon, these psyllids can be temporarily abundant; but their populations soon decline naturally, as they are attacked by their natural enemies, including parasitic wasps."

For some, even small blemishes on a plant will be annoying, but in a nature preserve, the long-sustained give and take between the plant and animal worlds is part of a complex food web to be celebrated. 

We could wish that the beech and the introduced nematode that threatens it would ultimately come into a balance that allows coexistence, but other native tree species laid low--chestnut, elm, ash--remain marginalized, even, as in the case of the American chestnut, more than a century later.

Campus Grounds Sprout Local Flora

Some areas of Princeton University's intensely landscaped campus are starting to sprout local native flora. Using native plants doesn't necessarily mean those species will be found in local nature preserves. Many native plants popular in landscaping--purple coneflower, red buckeye, bottlebrush buckeye, oak-leaved hydrangia, witch-alder, Virginia sweetspire--are seldom or never seen growing on their own in the local wild. 

But recently, the University has been planting the actual species frequently encountered in local nature preserves like Herrontown Woods and Mountain Lakes. This spicebush shrub in front of the Lewis Center for the Arts, 185 Nassau Street, resonates with the spicebush  so common in our woodlands.  

 

Turf has been replaced with a sedge meadow, probably the same Pennsylvania sedge that can be encountered in remnant meadows in local woods.

Masses of Christmas fern now grow on campus as they do along the slopes of the Princeton ridge.

A few species, like the foamflower making this mass of white, are rare to nonexistent in local woodlands, but the overall trend seems to be to treasure what is authentically local. 

Though some of the University's early efforts to plant native landscapes became overrun with weeds, this 2-3 year old planting down near Robert's Stadium is thriving. Better soil prep and thick mulch (and more knowledgeable gardeners?) have, at least thus far, conquered the weeds. The native species chosen are again those one finds in the local wild: cutleaf coneflower, arrowwood Viburnum, and wild rye grass. 

People naturally want to plant things that are special, and special used to be defined by distance--as in exotic plants imported from distant continents. Distance made the botanical heart grow fonder. It's heartening to see a shift in what is viewed as special, towards a valuing of what is truly local.