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, 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)”.