Stinking Fleabane, Dittrichia graveolens

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Stinking Fleabane, Dittrichia graveolens, by the A47 Norwich Southern Bypass. 26th September 2021.

NFN (New For Norfolk)

At the end of September my friend Chris Lansdell told me about a new plant for Norfolk, Stinking Fleabane, Dittrichia graveolens. Louis Parkerson had found a patch of it on the previous Tuesday and reported it on Twitter on 23rd September. Louis had seen similar plants growing by a motorway in the Midlands a few days earlier and he managed to work out what it was. His identification was soon confirmed by other members of the Norfolk Flora Group who were familiar with the plant from their travels.

The Stinking Fleabane was growing by the A47 Norwich Southern Bypass bridge, so just a short bike ride away from home. I decided to go and see it (note 1).

There were actually lots of plants – probably 200 – and they were growing right next to the road. Cars rushed past were just feet away from where I stood to take photographs. Most of the plants had already gone to seed but there were still some flowers left.

I picked a piece of Stinking Fleabane to smell. I found it very aromatic but quite pleasant and I think “stinking” is far too harsh. To me, the plant smelt of camphor (note 2).

Stinking Fleabane, Dittrichia graveolens

Stinking Fleabane, Dittrichia graveolens

Stinking Fleabane, also known as Stinkwort and Stinking Aster, is a member of the daisy family, the Asteraceae. It is one of two species of Dittrichia found in the British Isles, the other being Woody Fleabane, Dittrichia viscosa. Both are introductions (neophytes). Woody Fleabane appears to be declining in Britain but Stinking Fleabane is increasing its range (note 3).

In the British Isles, Stinking Fleabane is a long way from home. It is a native of Southern Europe, North Africa and Western Asia (as far east as Pakistan). In its native region it grows on roadsides, waste and fallow ground, hill slopes and also in damp habitats (note 4). It has been introduced into other parts of the world too: the United States, Australia and other parts of Europe  (Austria, Belgium, the Czech Republic, Germany, the Netherlands, Slovenia, Switzerland, and the United Kingdom. It reached Romania in 2020.) and Africa (Egypt, South Africa).

Dittrichia graveolens is an annual subshrub which grows up to 130cm (52 inches) tall. It has long and narrow leaves and these are pointed at each end with glandular hairs on the surfaces and small teeth along their edges.

Seedy Success

As an annual, Dittrichia graveolens needs to flower and set seed in order to survive. It is very good at this: each plant produces numerous yellow flower heads, each with as many as 16 ray florets and 40 disc florets and a single plant is capable of producing up to 71,000 seeds. It has been suggested that just one plant could produce up to 14,493 adults in the next generation. Scientists in California studying the seed and germination biology of Dittrichia graveolens found that the seeds are only viable for two to three years, with most germinating immediately after rain, from autumn through to spring.

Stinking Fleabane seeds are carried on the wind by means of the fluffy parachute (pappus) typical of many Asteraceae, and they can also float off on water to a new site. Seeds can be also be spread by vehicles, and this is presumably why the plants are growing by the A47.

The plant is thought to have arrived in Australia from Germany as a contaminant of wheat seeds but the seed’s pappus has barbs that allow it to attach to animal fur and the plant has moved elsewhere around the world in sheep’s wool. (The term wool-alien is used to describe plants that are spread in this way.)

At the time of writing, the NBN Atlas shows 45 records of Dittrichia graveolens for the British Isles, not including the recent discovery in Norfolk. In recent years the plant has also been found by the M5 in East Gloucestershire (2020) and by a slip road off the A299 in Kent (2014).   It is easy to imagine Stinking Fleabane spreading further along roadsides and eventually becoming as widespread along major roads as the Danish Scurvygrass, Cochlearia danica, I wrote about in May 2016.

As long as it stays by the roadside, Stinking Fleabane shouldn’t become a problem. But in some other parts of the world, Stinking Fleabane has become a bit too successful for comfort.

Noxious Weed?

Dittrichia graveolens is now regarded as a noxious weed in California and in parts of Australia and in 2013 the United States Department of Agriculture (USDA) produced a report, the “Weed Risk Assessment for Dittrichia graveolens (L.) Greuter (Asteraceae) – Stinkwort“. (There is also useful information with references on the California Invasive Plant Council (Cal-IPC) website.)

The USDA report describes how the plant became one of the the worst weeds in cereals in South Australia just thirty years after it was introduced to the state. By 2001 the plant was under an eradication program in Queensland, though its impact in South Australian cereal fields had lessened as soils became more fertile. Dittrichia graveolens has also spread rapidly in California since it was first discovered in 1984 and also occurs in Connecticut (since the 1930s), New Jersey, New York, and South Carolina.

Grazing animals tend to avoid Stinking Fleabane plants except when they are young, which can lead to infested paddocks with little grazing value. But if there is nothing else to eat, animals will browse on the plants and this can result in tainted meat and milk. Worse, if sheep eat the flower heads, the barbed pappus hairs can puncture the gut walls and cause bacterial infections and death.

Prolonged handling of Dittrichia graveolens can cause allergic reactions and severe dermatitis in some people. A study from 2007 demonstrated how a 56 year old man developed allergic contact dermatitis after handling the plant. Picking a small piece of the plant to sniff (like I did) shouldn’t cause a problem but the advice “So, when pulling this plant out, be sure to wear gloves” is well worth following.

My photographs hopefully give a good idea of what Stinking Fleabane looks like but I also recommend the Italian Schede di botanica website if you’d like to see more pictures of the plant.

Notes

Note 1 – In the late 1980s and early 1990s Vanna and I sometimes went on day trips to see rare birds. We were twitching, but only on a very limited scale. Trips were confined to Norfolk and North Suffolk and relied on friends who could give us a lift in their cars. We never considered driving to Cornwall or flying to Fair Isle to see a rare bird.

One day in 1990 or 1991 we went to Lowestoft to see a Red-eyed Vireo, a North American vagrant. We failed! The bird flew out of the Sycamore tree it had been hiding in and we missed it, which ruined our day. We decided this was ridiculous – we had otherwise had a good day out.

Nowadays we only bother with rare birds if we’re in the area anyway (such as staying at Wells-next-the-Sea in October 2015, when northerly winds brought falls of migrants to Wells Pine Woods).

However, I will travel to see rare plants if they’re not too far away. Plants are not going to fly away and the odds on their survival are usually better than those of a rare bird blown off course and doomed to die many miles from home, without finding a mate.

Note 2 – The smell reminded me of Aztec Sweet Herb, Phyla dulcis, which I grew in a pot for several years.

Note 3 – Neophytes are plants introduced to the British Isles after 1492. Information from Clive Stace, “New Flora of the British Isles“, pages 775 – 776. (Fourth Edition, 2019.)

Note 4 – Information from Marjorie Blamey and Christopher Grey-Wilson, “Mediterranean Wild Flowers“, page 438. (Harper Collins 1993).

The 2013 United States Department of Agriculture (USDA) report, the “Weed Risk Assessment for Dittrichia graveolens (L.) Greuter (Asteraceae) – Stinkwort” gives the following native range: “Southern Europe (Albania, Bosnia and Herzegovina, Bulgaria, Croatia, France, Greece, Italy, Macedonia, Montenegro, Portugal, Serbia, Spain), northern Africa (Algeria, Libya, Morocco, and Tunisia), central Asia (Afghanistan, Cyprus, Iran, Israel, Jordan, Lebanon, Pakistan, Syria, Turkey), and tropical Asia (India)”.

Oak Bracket, Pseudoinonotus dryadeus

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The last few days have seen a sudden change from a very warm and sunny late summer to a much cooler and rather rainy start to autumn. Flowers and insects are on the wane but fungi are starting to appear.

I was cycling near Carleton Rode, south-west of Norwich, a couple of weeks ago and passed an oak tree by the roadside with some distinctive bracket fungi growing at its base and stopped to take a look.

They were the Oak Bracket, Pseudoinonotus dryadeus. 

Oak Bracket, Pseudoinonotus dryadeus

Base of English Oak tree with Oak Brackets, Pseudoinonotus dryadeus

Oak Bracket, Pseudoinonotus dryadeus

Oak Bracket, Pseudoinonotus dryadeus

In its prime, the Oak Bracket is extremely beautiful. Its velvety upper surface is cream to rusty brown with a yellower margin and is pitted with tubes. These ooze an orange-brown liquid that looks like runny honey, though, as the First Nature website points out, “it is not as tasty as honey”. The fungus is not edible – it is described as bitter and tough.

Oak Bracket, Pseudoinonotus dryadeus

Oak Bracket, Pseudoinonotus dryadeus, oozing nicely.

The Oak Bracket is a parasite, mainly on species of oak, although Beech, Birch and Alder and Maple, Elm and Sweet Chestnut are occasional hosts. The fungus causes a white rot in base of the trunk (“butt rot”) and eventually branches can die off and the weakened base of the tree can make it prone to toppling. Spores enter through wounds in the tree’s bark so this is “one of many reasons not to damage tree bases with lawn mowers or other equipment“.

The Oak Bracket grows as an annual bracket without a stem. The ones I saw were in their prime; older specimens become corky and fibrous. The caps become blackened and cracked over winter, and sometimes persist for several years. They apparently smell very unpleasant. (The ones I found just smelt slightly mushroomy. I must go back and have a sniff when they’re older!) (See April 2022 update below.)

Oak Bracket is also known as Warted Oak Polypore, Weeping Polypore and Weeping Conk. The last two names refer to its habit of oozing liquid, but it’s worth knowing that other species of bracket fungus also weep. Two examples are Shaggy Bracket (Inonotus hispidus) , found especially on Ash and Apple trees, and Alder Bracket (Inonotus radiatus), found on Common Alder.

The Oak Bracket’s original scientific name was Boletus dryadeus and prior to 2001 the accepted name was Inonotus dryadeus, which is still used in some field guides (such as Sterry and Hughes) and on some websites (e.g. Wikipedia, Messiah University).

The First Nature website has some good pictures of the Oak Bracket. It also tells us generic name Pseudoinonotus comes from pseudo (false), ino (fibrous), ot (ear; also used in Otidea bufonia, the Toad’s Ear fungus) and –us (making it a Latinised noun). The specific name dryadeus means ‘found with or on oak trees’.

Pseudoinonotus dryadeus is commonest in the southern half of the British Isles. At the time of writing the NBN Atlas lists 292 records, with just three in Scotland. It also occurs elsewhere in temperate parts of Europe and in North America.

The Oak Bracket shouldn’t be confused with the Oak Polypore (Piptoporous quercinus), which is very rare in the British Isles and grows only on veteran oak trees (though there is apparently one old record on a Beech).

Cross section through a Crunchie

Cross section through a Crunchie bar.

When fresh Pseudoinonotus dryadeus also resembles a section through a Crunchie Bar but the taste, difference in size and presence of a chocolate coating on the latter should avoid confusion.

April 2022 Update

I did go back and sniff the Oak Bracket, in December 2021. The fruitbodies were now greyish black. There was no smell at a distance but if I sniffed the surface I could just detect  a not very pleasant nitrogenous smell of rotting fungus, like a cultivated mushroom that had been sweating in the fridge for too long.

I cycled past again on 10th April 2022 and was shocked and saddened to see that the Oak tree had gone. The gales in late February may have toppled it, or a farmer or tree surgeon may have seen the brackets and decided to remove the tree. There were only some thin twigs left, plus a few shattered remains of very woody (and not at all smelly) Oak Bracket on the ground. I took one home as a souvenir.

Broad-leaved Ragwort, Senecio sarracenicus

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Broad-leaved Ragwort, Senecio sarracenicus

Broad-leaved Ragwort, Senecio sarracenicus at Wheatfen. Growing along the edges of the wood, where it looked as if it was part of a wild herbaceous border.

I’m lucky to live close to some very special places, one of which is Wheatfen Nature Reserve, on the south bank of the River Yare just east of Norwich. I visited a couple of weeks ago to look at plants and late summer insects, and walked through Home Marsh, a part of the reserve I haven’t visited before at this time of year.

I found a new species (for me), which I had to look up in my books when I came home: Broad-leaved Ragwort, Senecio sarracenicus. It is a statuesque plant, clearly a type of Ragwort, with the typical yellow daisy flowers, but with broad leaves, green on both the upper and lower sides. It was growing in large clumps in the marsh and along the edges of the wood, where it looked as if it was part of a wild herbaceous border.

Broad-leaved Ragwort, Senecio sarracenicus, is a hardy perennial that grows to 1.5 or even two metres tall in damp places and is in flower from July to September (and possibly earlier in some places: the Wildflower Finder website says it flowers from May to July). It is a member of the Asteraceae (formerly Compositae, the Daisy family) and a close relative of the superb wildlife plant our native Common Ragwort (Jacobaea vulgaris).

In the British Isles, Senecio sarracenicus is a neophyte and was introduced in 1632 (note 1). It is a native of other parts of Europe, to Siberia and Turkey. The NBN Atlas website has a map of British records, though this misses out the known sites in Norfolk: Wheatfen, Hoveton and Martham (note 2). Most records are from Scotland and the north of England.

The Wild Flower Finder, UK Wildflowers and Nature Gate websites have some good photographs of Broad-leaved Ragwort, which was formerly known as Senecio fluviatilis. Its older English names include Saracen’s Woundwort, Saracen’s Comfrey and Saracen’s Consound.

So why is Broad-leaved Ragwort growing at Wheatfen?

I found the answer in a booklet I’d bought on a previous trip to the reserve (note 3).

For forty years Wheatfen was the home of by Ted Ellis (1909-1986), the naturalist, writer and broadcaster (note 4).

In the 1930s Ted tried to reintroduce the Large Copper butterfly to Wheatfen. The butterfly used to occur in fens in East Anglia and Lincolnshire and was “once widespread” at Wheatfen. He planted Broad-leaved Ragwort to provide late summer nectar for the Large Coppers.

The Large Copper’s foodplant is Water Dock (Rumex hydrolapathum), which is abundant on the reserve but the project failed, as did the more well known reintroduction at Woodwalton Fen (note 5).

The plant lives on and is thriving, long after the Large Coppers – and Ted Ellis – have gone.

Broad-leaved Ragwort ,Senecio sarracenicus

Broad-leaved Ragwort, Senecio sarracenicus

Notes

Note 1 – From p72,  ‘Alien Plants’ by Clive A. Stace and Michael J. Crawley (Harper Collins, 2015). Neophytes are plants introduced to the British Isles after 1492.

Note 2 – Gillian Beckett, Alec Bull and Robin Stevenson, ‘A Flora of Norfolk’. Privately published. (1999).

Note 3 – The Ted Ellis Trust. ‘Wildflowers of a Broadland Reserve Wheatfen. Part 1: Species of the fen and reedbeds.’ (Written by Will Fitch, the current warden.)

Note 4 – My first encounter with Ted Ellis was as a child, when I had several of his wildlife guides, packed full of photographs, published in Norwich by Jarrold Colour Publications and written by “E.A. Ellis”. At the time I didn’t imagine I would one day live in Norwich.

After his death, the Ted Ellis Trust was set up to look after Wheatfen.

Note 5 – The Large Copper reintroduction project at Woodwalton Fen ran from 1927 until the early 1990s. Our own sub-species, Lycaena dispar ssp. dispar became extinct in 1851 (or perhaps as late as 1864), so the Dutch subspecies, Lycaena dispar ssp. batavus, was used.

I visited Woodwalton Fen on a Botany field trip in 1983 and while I was there I saw several Large Coppers flying in the warden’s greenhouse, but sadly not in the wild.

‘The Butterflies of Britain & Ireland’ by Jeremy Thomas and Richard Lewington (British Wildlife Publishing, 2014) gives more useful information.