Category Archives: Senecio

Invader, or just a plant on the move? The case of Senecio inaequidens

Senecio inaequidens

Senecio inaequidens

This is a sibling of the common groundsel – a species in the same genus – but found mostly in the Mediterranean region, and on the Atlantic coast. It forms low tufts of yellow aster-like composite blooms, easily identifiable by its straight, linear leaves and ragged petals: the word ‘inaequidens’ means ‘unequal teeth’.

A tuft of Senecio in the vines

A tuft of Senecio in the vines

I’ve seen this flower a lot throughout the year, and especially lately when there’s not much other colour around. But it’s hard to find in the standard flower guides, and this may be because it’s judged to be an invasive species. Eventually I identified it with the aid of some botanic websites, and this raises two questions: do you really need an expensive illustrated flower guide these days if you have internet, and what does ‘invasive’ really mean?

The first question was also prompted by a friend in the village who wanted a guide which grouped plants by colour, and asked me to recommend one.  I think the answer is ‘Yes, you do need one…..but only one’, because of the excellent resources on the web, which I’m going to review in my next post.

The issue of ‘invasion’ was raised in my last post by the two arrivals from South Africa: Carpobrotus edulis and Aptenia cordifolia, and I wanted to explore it a little more. There seem to be three major factors in judging invasiveness: when the plant arrived, how it arrived, and what consequences there are for previously-established flora and fauna.

So, the ‘when’ factor: the divide is the Columbian date, for practical purposes 1500 AD, when world trade is reckoned to have started.  Those plants which arrived before then are ‘archaeophytes’ (old plants) – for example the poppy (Papaver rhoeas) which ‘invaded’ Europe in batches of seeds of cereals, several thousand years ago.

Poppy - familiar but invasive?

Poppy – familiar but invasive?

This post’s featured plant, Senecio inaequalidens, arrived in modern times, between 1934 and 1936 when its seeds were included in bales of sheep’s wool imported to Mazamet in southern France from the Cape of South Africa, as its French names, Séneçon du Cap, or  Séneçon de Mazamet, testify. It is thus a ‘neophyte’. New plants are more of a threat because we – and the ecosystem – have had more time to deal with the old plants, and many ‘old’ invaders are useful – apples, pears and apricots all came from the Far East.

The ‘how’ factor seems to depend on the degree of human involvement and the distance carried – seeds carried on shoes and burrs on clothing travel typically only short distances, part of a natural pattern of dispersal. The long-distance transport of Senecio, although a likely consequence of trading, was not as deliberate as that of Carpobrotus and Aptenia since they were sought as garden plants, even if their escape has been unintentional. Travellers to Australia and America will know the precautions taken at Customs to exclude non-native species of plant – a gardening friend of ours from Adelaide would have loved to take back seeds, but knew she couldn’t.

And why couldn’t she? Because of the third factor, the consequences. Plants from far away often arrive where they have no natural pests or predators, and may find a climate and soil much more beneficial than the one in which they evolved to survive. If they have drought- or frost-resistance and some clever means of propagating in addition, they can spread like wildfire and supplant native species. An example familiar in Britain is the spread of Rhododendrons in wild areas of Snowdonia, after they were brought from the Himalayas in the 19th century to put in gardens, from which they escaped. Another is goldenrod ( Solidago canadensis), brought from North America to European gardens as an ornamental plant: it displaces native vegetation of fallow land in central Europe, especially in Germany where it is classed as invasive.  The Black Locust tree (Robinia pseudoacacia) is native to the south-eastern USA, but has been widely planted in European city parks and roadsides because it tolerates pollution. Its seeds spread easily and now threaten some woodland communities especially in dry, poor soils.

What’s the bill for Senecio? Fairly resistant to frost (unlike the two succulents – we lost our pot of Aptenia last winter when it was minus seven), and to drought.  It can be pollinated either by insects or wind, so it sets a lot of seed, which can be wind-dispersed –  it doesn’t depend on an animal which might have been lacking in its ‘new’ home. The plant is toxic to neighbouring plants, and to most animals in this area, so it’s not eaten – except by one caterpillar.  All these factors mean it has spread widely, though its range seems restricted to the milder climates of the Mediterranean and the Atlantic coast to Bordeaux.

Map from tela botanica showing reports of Senecio in France

Map from tela botanica showing reports of Senecio in France

So is it an invasive nuisance? On many counts, yes: a recent arrival, from far away, brought by human agency, and evolved to survive in the poorer soils of the Cape. And that’s probably why it’s not in many wild flower guides. But in practice the consequences are, so far, manageably small in the Midi at least, where it hasn’t taken the niche of a ‘native’ plant, and doesn’t threaten the established vines, regular ploughing and herbicides restricting it to the borders of vineyards and roadsides.

Jared Diamond

Jared Diamond

To apply the label ‘invasive’ is of course a bit of a nerve, when the most invasive species of any has been Homo sapiens. I’ve just been reading Jared Diamond’s fascinating book Guns, Germs and Steel, in which he shows how humankind spread from its African origins, and how disparities between human societies arose. He makes it clear, for example, that humans first arrived on the American continent via the Bering Strait and Alaska and entered what is now North America before 11,000 BC, and within a thousand years had spread to reach Tierra Del Fuego at the tip of South America.  Along the way they hunted to extinction most of the large mammals they met, leaving little to domesticate and hence little incentive to settled, productive farming.  The same story had been played out 40,000 years before in Australia when humans first arrived in that hitherto man-less continent from Indonesia – the animals for which fossil evidence exists all vanished, presumably eaten. Hunting small species and gathering was the only option left for the people who became called Aborigines. Our literal appetite for destruction and lack of foresight as a species does not bode well for our ability to face the current and pressing environmental challenges which we ourselves have caused, such as global warming and the spread of disease. You can hear a BBC interview with Prof. Diamond if you click here – it should be available at least till the end of 2013.

The case of Senecio inaequalidens reminds me that the pattern of plant dispersal is a story of constant change – we can’t define, let alone preserve an exclusively ‘native’ flora, just as we can’t define British, French or Catalan or any other race of people.  The movement of musicians and musical styles is a further example, in fact I have a theory that music is only developing when it’s moving and finding new territories – jazz moving out of New Orleans, R&B arriving in Liverpool, Arabic and western musics meeting in medieval Spain.  And here’s another example – the travels in the mid 60s of South African musicians, such as saxophonist and composer Dudu Pukwana, forbidden to play with white musicians or for mixed audiences in their own country, thus starting a stream of African influence in jazz. Dudu Pukwana was a strong element of Chris McGregor’s Blue Notes, and then of his Brotherhood of Breath.

This is Dudu Pukwana and Spear – ‘Sonia’  – from In the Townships, 1973.

Coming up next: Top of the bots – Which botany website?

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