Aliens and Invasives

Intriguing recent plant discoveries

Asclepias tuberosus (butterfly weed) with golden leaves. Image ©GardenPhotos.comMaking the hour’s drive back and forth to my cardiac rehab three times a week, and often walking woodland trails on the other days, I’ve spotted some interesting plants along the way.

A couple of years ago I wrote about a yellow-leaved form of common milkweed, Asclepias syriaca, which I spotted growing by the side of the road and last week in a quiet area at the back of the radiology unit (yes, I was just poking around…)  I found a yellow-leaved plant of a different Asclepias species – A. tuberosa, butterfly weed. As you can see (left, click to enlarge) it looks very dramatic and doing very nicely amongst the crown vetch (Coronilla varia).

There were also normal green-leaved plants scattered about the area, which had clearly been disturbed during construction work so we’ll see if that coloring was the freak result of something nasty in the soil or a genuine mutation. I’ll stop back later in the summer for another look.

A white-flowered form of wild bergamot, Monarda fistulosa. Image ©GardenPhotos.comWhite flowered monarda

Just at the moment our local wild bergamot, Monarda fistulosa, is in full flower. This seems to be a “first respondent” if you like, one of those plants that quickly arrives in freshly disturbed soil on open sunny sites. It occurs as a few plants or in huge drifts which, when you look closely, include an occasional plant with darker, or paler flowers.

But this week I screeched to a halt as I spotted a plant - just one - with white flowers (abiove right, click to enlarge). It turned out not to be the white flowered species M. clinopodia (which has a few purple spots on the flowers), but a genuine white-flowered form of M. fistulosa (wild bergamot). There were only a few plants in that location, but I’ve marked it and will collect some seed later.

UPDATE That was a few days ago - and yesterday I found another one, twenty miles farther south. I've been all these years and never seen one white one, and now I come across two.

An Asian bush honeysuckle with attractive amber berries. Image ©GardenPhotos.comAsian bush honeysuckles

I’d never stopped to look closely at all the shrubby honeysuckles along the roadside (please forgive my severe dereliction of botanical duty), they’re growing along a stretch of road where it’s not safe to stop the car. But they’re quite a sight in May when covered in white or cream or pink or red flowers, and again now when they’re in fruit.

Then in a parking area the other day I spotted a plant with lovely amber orange berries (left, click to enlarge). Frankly, I’m not sure if it’s Lonicera maackii, L. morrowii, L. tatarica, or L. x bella (the hybrid between L. morrowii and L. tatarica)  – all of which are collectively known as Asian Bush Honeysuckle; I’ll have to make more of an effort to check them when they flower next year. But, although I know they’re all rated as invasive, they’re very attractive especially those with brilliant scarlet berries (rather than a dull and dirty red) and this pretty amber berried form.

Variegated oak

And finally, on the way up the hill to the ledge from which I shot this wonderful picture of a field of Black-eyed Susans (Rudbeckia hirta) – a variegated oak seedling (below, click to enlarge). I think this may be the only one I’ve ever seen outside a botanic garden, and here it is growing by a woodland trail in Pike County, Pennsylvania.

Variegated seedling of red oak, Quercus rubra. Image ©GardenPhotos.comIt’s a seedling of red oak, Quercus rubra, and a quick online search for variegated red oaks reveals only ‘Greg’s Variegated’ and one named as 'Foliis Variegatis' in the Journal of Arboriculture in October 1987. It’s growing very near the trail; I may have to move it to the garden in the fall.

The only other one I’ll mention here is the vanishing trumpet vine (Campsis radicans). There are occasional plants all the way along my drive, all with the usual orange flowers. But, last week, I spotted one cluster of purplish red flowers.

There was too much traffic to stop examine it but it turns out this is a known variation - ‘Atropurpurea’ – but very rarely seen. So rarely seen, in fact, that when I did stop a few days later – I couldn’t find it!

Book Review: Where Do Camels Belong? by Ken Thompson

Where Do Camels Belong?: Why Invasive Species Aren't All Bad by Ken ThompsonIn Britain, this invaluable book is subtitled The Story and Science of Invasive Species; in North America, the more provocative subtitle is Why Invasive Species Aren't All Bad. Both are appropriate; look dispassionately at the science and it’s clear that invasive species are not all bad.

So often, discussions of the whole issue of natives and non-natives (plants, animals, insects and the rest) are run through with the repetition of bold assertions, unproven by science, that it’s a relief to find a book in which the whole issue is viewed more calmly, in a broad context, considered over time, and backed by solid science. It's just what we need: more unbiased science and less thoughtless hysteria – and that is what this book provides. And it’s all presented in a lively, and very readable.

Ken Thompson discusses how we define “native” and how we stretch our objective definitions to take account of subjective impulses; he reveals how little we actually know about so many non-native species and how very few ever cause problems; he examines whether the most hated invasive species really are as destructive as we’re told and points out that some have positive impacts; he discusses how natives and non-natives can happily co-exist in the same habitat; he applies science to the myths surrounding invasive species.

One of the striking features of the response to the presence of non-native plants, in North America in particular, is the frequency with which they’re simply removed – just in case – rather than studied. As Dr Thompson points out, the proportion of non-natives that arrive in natural habitats and end up causing problems is minute. And when non-natives are studied over the long term, we sometimes find that their initial dominance is followed by a sharp decline followed by a stable balance.

I won't steal the author’s thunder by summarizing his invaluable discussion of how we define the word “native”, except to say that picking any date as a cut-off point after which an arriving species is declared an alien is clearly arbitrary and ignores the fact that ecosystems have always evolved over time and continue to do so. And suggesting that only new arrivals in natural habitats that are unassisted by man can be classified as “native” ignores the obvious fact that nowhere on the planet is unaffected by man’s influence, so nowhere is genuinely “natural” anyway.

So. What a refreshing book and one that’s full of stimulation and reminders to look at the evidence and not listen to the hearsay. This book effectively skewers the prejudices and pseudoscience of the plant police extremists for whom natives are, by definition, good and non-natives inherently bad. It should be read by anyone with an interest in native and non-native plants, by those working in the field, and also by natural history and garden writers like me - so we don't simply repeat misconceptions in our work. The book is stimulating and refreshing: as soon as I got to the end I immediately started again at the beginning. [The anwser to the book's title, by the way, is a fascinating one. Needless to say, it's not what you think.]

Where Do Camels Belong?: The story and science of invasive species by Ken Thompson is published in Britain by Profile Books. It will be published in North America as Where Do Camels Belong?: Why Invasive Species Aren't All Bad by Greystone Books in September. North American readers who are eager to read it before September can order the British edition from


Rampageous wisteria in the Pennslyvania woods

Wisteria floribunda smothering the Pennsylvania woods. Image ©GardenPhotos.comInvasive plants keep turning up on these pages, and often I’m less than supportive of the way the plant police want to rip out any non-native plants that turn up in wild places – as with the snowdrops I wrote about last month - whether or not they’re doing any harm.

Well, here’s one that we can justifiably worry about.

I spotted the bluish purple flowers hanging from the branches as I drove between the woods and the Delaware River in Pennsylvania the other day. That's Wisteria, I thought. I was on a tight schedule and couldn't stop, so when I got home I checked with the Pennsylvania Flora Project website which told me that no wisterias, native or introduced, grow in the area. The USDA plants website said the same thing.

Yesterday I was again passing that way and took a closer look. Yes, it’s wisteria – but the Japanese Wisteria floribunda (below, click to enlarge) and not the uncommon Pennsylvania native W. frutescens which flowers later and has much shorter strings of flowers. And it’s not just a plant or two, there must be half a mile of it in half a dozen different places over a stretch of a few miles. It's covering the trees(above, click to enlarge).

This is in the Delaware Water Gap National Recreation Area, where you’d expect some expert oversight of These strings of flowers of the Japanese Wisteria are longer and earlier than those of the native species. Image ©GardenPhotos.comthe habitat that’s being preserved, and one stifling mass of it is by the turn to the Pocono Environmental Education Centre. So why do the distribution maps say that it doesn’t exist in the area? I presume that, like the hellebores I wrote about a few weeks ago, it originated on a now-vanished property. When it was planned to flood this valley to create a reservoir many houses were vacated and removed - but not the plants. But it’s clearly been there a long time, so it’s strange that no one noticed -or, at least, no one reported it.

Of course, it looks spectacular but it completely smothers and weighs down the trees. Clearly anything growing on that scale – 30 to 40ft high, and more, through trees – must be doing some damage. I wonder if anyone has published any before-and-after wisteria research.

Snowdrops invasive?

Snowdrops naturalized in Pennsylvania: 2009. Image ©GardenPhotos.comBrits may think it a little strange for me to be writing about snowdrops in the last week of April but, here in Pennsylvania, we still have flowers on ours. And recently, for my first solo excursion in the car since my hospital stay, I went to take a look at some snowdrops (Galanthus nivalis) growing in the woods a few miles away. I suspect that the site is that of an old homestead - itself long gone.

Of course, snowdrops are not native here in North America; in fact, many enthusiasts for native plants describe them as alien invasives and spend a great deal of effort removing what they describe “infestations” or spraying them with weed killer. Japanese knotweed – OK, fair enough; but snowdrops?

So it was interesting to revisit these local snowdrops, which I last looked at five years ago (above left, click to enlarge), and to see how few there now are (below right, cick to enlarge)– there are probably about 10% of the number there were when I first came across them. Snowdrops naturalized in Pennsylvania: 2014. Image ©GardenPhotos.comAnd this is a factor that’s rarely monitored here in North America where the demand for instant removal of any plant that’s not native rings so loud: while non-native plants may establish themselves in wild communities and start to spread, they may also then decline and fade away.

And anyway: snowdrops are not exactly known for their capacity to smother other plants, in the wild or in the garden. In Britain, where they’re also not native, snowdrops are enjoyed and appreciated in the wild as delightful and harmless early season flowers. In the US, they’re eradicated.

Double daylily of the roadside

Hemerocallis fulva 'Flore Pleno' is a familiar roadside plant here in north east Pennsylvania. Image ©
Last time I discussed a familiar roadside plant here in Pennsylvania, brought with the settlers to make soap – Saponaria officinalis, soapwort. But alongside it we often find a very different, but equally robust perennial, from Asia this time, the double-flowered daylily Hemerocallis fulva ‘Flore Pleno’.

If it wasn’t for the vast variety of more recent daylily hybrids, this would be on everyone’s list of top perennials. With its long season of 6in/15cm double flowers, each a nest of ochre orange petals, the outer petals are broad and bold with a bright red flash, the inner ones narrower with a less dramatic mark.

This is a triploid plant, with an in between number of chromosomes, so it cannot set seed and this helps prolong its flowering season which is most of July, often starting in late June or extending into August depending on the local climate. It reaches about 3ft/90cm, is dependably self-supporting and unlike many daylilies spreads by stolons to make large patches.

‘Flore Pleno’ is also reckoned to be the top choice for cooking, deep frying in particular. I’m told that with so many more petals in its large flowers it makes much a more of a mouthful than the usual six petalled daylily. The tubers are also edible.

In gardens, Hemerocallis fulva 'Flore Pleno' is a colorful, trouble-free perennial. Image ©GardenPhotos.comHemerocallis fulva grows wild in many Chinese provinces as well as in India, Japan, Korea and Russia. ‘Flore Pleno’ was brought to Europe from Mauritius by the Reverend W. Ellis and passed to the influential British nursery Veitch & Sons some time before 1861. From there it came to North America where it flowered dependably with little or no care – as it does along roadsides

‘Flore Pleno’ is sometimes confused with another daylily, H. fulva ‘Kwanso’. Both are double, and both have orange flower with red marks on the petals. However, the most clear distinguishing feature is that ‘Flore Pleno’ has 15 to 18, strongly recurved petals usually arranged rather neatly, while ‘Kwanso’ has seven to twelve petals, often in a rather muddled-looking arrangement. Neither ever produced seed, although both have partially fertile pollen.

Daylily enthusiasts often look down on this plant because it’s less refined than modern hybrids, in a less surprising color and without the intricate patterning of so many recent introductions. But, if you like the color, and are looking for a summer perennial that you can plant and pretty much ignore then this is it.

On the road

It’s been a bit hectic recently. I've been galloping round Britain visiting plant breeders, nurseries, gardens, family and friends - I did more than twice as many miles as usual - and readying the house for some major building work.

I saw some impressive new Shasta daisies (Leucanthemum) on trial (above, click to enlarge), a field of 10,000 buddleias, a delightful new fragrant verbena, grafted melons, hundreds of different heucheras, some dramatic variegated euphorbias and variegated phlox, cultivated wildflowers like a field of jewels, spectacular angel pelargoniums for patios, and much more. And the first two weeks was accompanied by the superb BBC radio coverage of the Olympics on the car radio.

I’ll be bringing you more on these sights and discoveries, but it wasn’t just the nurseries and gardens that held so much appeal. After a very wet summer the roadsides were unusually colourful for August with scabious in particular in clouds of soft blue.

And one of the last roadside flowers I saw on the road to the airport to fly out from the US was also one of LathyruslatifoliusRoadside_G022228the first I saw after landing in Britain. The perennial pea, Lathyrus latifolius, was sprawled through the roadside grasses on both sides of the Atlantic having spread from gardens far from its natural habitat in Southern Europe and North Africa. I shot the picture on a steep skope in British a gale when I feared rolling down into the traffic (rifght, click to enlarge). But I was also able to cut spikes from the blushed white form growing in our English garden (once I’d untwisted the bindweed) which made a prettty posie with some pink rosebuds.

Heathrow euphorbias

Euphorbia characias on the M25 near London's Heathrow Airport. Image ©
A surprise driving away from London’s Heathrow airport the other day. There’s a huge intersection where the road from Heathrow joins the M25, London’s 117 mile, six and eight and ten lane, orbital motorway. At one point there’s a traffic light and there, by the side of the road, spilling out through the fence, were three huge euphorbia plants, Euphorbia characias.

So, I drove - carefully - all the way round again, extracting my camera from the bag on the seat alongside me as I went. I manoevred across into the lane alongside the euphorbias and – the lights had changed. I came to a halt in just the right spot, snapped three quick pictures out of the window before the lights changed to green, and I was on my way home. One picture was sharp –ish (above, click to enlarge).

This is not a British native plant, it’s from the Mediterranean, but I’ve always grown it. But on a roundabout on the M25? There are no gardens for miles. I bet some mischievous passing gardener threw a few seeds out of the car window. I'll be keeping an eye on them from now on.

Does this make me a bad person?

LysichitonCamtsch900Not long after we moved to Pennsylvania, I planted two plants at the edge of the little creek that flows through the corner of our property. It was all a bit bare, and I thought some quietly colourful plants would brighten things up.

One that I planted was Lysichiton camtschatcensis. This is the white flowered Russian version of the yellow flowered American native Lysichiton americanum. As the name indicates, it comes from the Kamchatka Peninsula, just across the narrow Bering Strait from Alaska. Sarah Palin must have had a good view.

For the first few years, all that happened was that the plant slowly - very slowly - became larger. Then it produced a single white flower, and as far as I could tell the seed head was eaten by deer. Then there were two flowers, then, ten years after planting, this year three lovely white flowers appeared. But the point is that a few yards farther down the stream a second plant flowered this year, as you can see in the background in the picture (click to enlarge).

So it’s started to spread down the stream. Some seed must have escaped the deer and germinated and the resulting plant has now reached flowering size. I have to say that I was very pleased to see that some seed had escaped the deer.

But. So. Here’s the thing. Should I rip them all out to ensure that this non-native plant does not continue its spread downstream? Should I watch and wait and see what happens? Or should I just not worry about it, and simply admire them? I’m planning to watch and wait but not tear them out – does that make me a bad person? Should I playDarmera-peltata-_G010731 safe, and just dig it all out?

Oh, yes, the other plant I put alongside the stream was Darmera peltata ‘Nana’, the dwarf form of what used to be called Peltiphyllum peltatum, with clusters of pink flowers in spring and wine red fall foliage. It grew well for the first half of the first season - then the deer ate it and I never saw it again. So no chance of that spreading.

Acres of celandines

As far as the eye can see… Celandines, carpeting the damp woods at Black Brook Park in Union County, New Jersey. We were out there the other day, taking a family stroll.

And after marveling at vast acres of skunk cabbage growing along the muddy stream, we turned a bend in the trail and, on slightly drier ground, were the celandines, like a vast green ballroom carpet scattered with yellow confetti. I don’t think I’ve ever seen so many in one place.

Lesser Celandine, Ranunculus ficaria, is a widespread British native perennial with roots like tiny dahlia tubers. Very early into growth, its waxy green leaves are topped with flowers like buttercups. Later in the season it completely dies away. The whole plant rarely reaches 8in/20cm in height. It’s common wildflower and an irritating garden weed in Britain, spreading by seed but also when the clusters of tiny tubers break up. RanunculusficariaBrazenHussy700

In North America it’s known as the Fig Buttercup – from the shape of its bright green leaves and its yellow flowers - and is becoming widespread in the east and Pacific North West. Its rated as “Invasive, banned” in Connecticut and “Prohibited” in Massachusetts. Looks fantastic, but big big trouble: like the kid you saw at the bus stop on the way to school…

At Black Brook Park it was present in acres of vast drifts although in places spring beauty, Claytonia virginica, was holding its own. But it’s plants exactly like claytonia, the early spring ephemerals, that are smothered by the mass of dense early celandine foliage. However, I was also surprised to see a few patches of snowdrops, Galanthus nivalis, looking lush as their foliage stretched after flowering last month.

I could have spent all day examining this huge population of celandines, but a short look indicated that they were very uniform, apart from a few with unusually narrow petals and a few with paler flowers.

Ranunculusficaria-foliage23009In Britain, it’s different. While everywhere at Black Brook Park, New Jersey, the plants had plain green leaves, in Britain the foliage can vary enormously. I picked the leaves in the picture (left, click to enlarge) from a few hundred yards along a quite Sussex lane. The bronze-leaved variety that Christopher Lloyd named ‘Brazen Hussey’ (above, click to enlarge) was found wild in a wood on his property. Other unusual forms, like doubles, also turn up.

But here’s the thing… That sunny carpet of color, disappearing into the distance in that New Jersey park, looked absolutely magical. Is it less beautiful because we know that the plant is not a native?

Coltsfoot: the bad and the good

Coltsfoot by a Pennsylvania roadside, with cigarette butt. Image ©Garden
This week, here in Pennsylvania, the roadsides are bright with a colorful wildflower at its peak. OK, of course, it’s not actually a Pennsylvania native, or even an American native, but it sure looks sunny.

Coltsfoot, Tussilago farfara (above, click to enlarge), is a widespread British plant which presumably came over with colonists. In Britain it grows in many sunny places, often on heavy soils, and it’s been a difficult agricultural weed; its white runners are certainly very resilient.

In the US, it’s now found in much of the east and north east, and in the Pacific North West, while in Pennsylvania the USDA distribution map reveals that our county, Pike County, in the east of PA, is one of the few where it’s not found. Don’t think so: see pictures.

Pennsylvania roadside population of coltsfoot, with beer can. Image ©GardenPhotos.comHere in the US, I’ve only ever seen it on roadsides (left, click to enlarge) and in roadside parking areas although the Flora of Pennsylvania reports it “on roadsides, railroad rights-of-way, stream banks, and waste places” – which is pretty much exactly the language used to describe the distribution of Japanese knotweed. The implication being that man’s activities spread it along roads and where road meets river the river takes a hand. In Alabama it’s noted as “Class A noxious weed”; in Connecticut as “Invasive, banned”; in Massachusetts it’s “Prohibited” while in Oregon it’s an “"A" designated weed”. Sounds like it can be a bit of a beast.

But why “coltsfoot”? Well, this more or less describes the hoof-shaped leaves which emerge when the flowers are done. So it’s also been known as horse-hoof, and foal’s foot.

But this is actually quite a useful plant. It turns out – courtesy of Geoffrey Grigson’s wonderful book The Englishman’s Flora – that not only were the dried leaves once smoked to alleviate asthma, but that it’s still an ingredient of herbal tobacco. And, in the long gone days of tinder-boxes, the silver down on the backs of the leaves was collected as tinder. (What a job that must have been.) So perhaps plants were brought to the new world because they were so useful. It seems, in the US at least, they’re now becoming rather the opposite.

But, here in Pennsylvania, I like to see them brightening up the roadsides in spring. Just warming us up for the dandelions - of which more another time.