Wednesday Weed – Bladder Senna

Bladder senna (Colutea arborescens)

Dear Readers, having spotted this plant growing over a railway embankment en route to Blackhorse Road tube station I couldn’t resist doing a post on it. At first, I thought that the poor thing had been attacked by some particularly unpleasant insect. Plus, does anyone else think that the seedpod with the seeds in it looks like the skull of a Tyrannosaurus Rex? The flowers are pretty too, but it’s the pods that really make it stand out.

My photo of the flowers. Taking a picture from the front would probably have been a good idea….

Photo One byBy AnRo0002 - Own work, CC0,

A rather better photo of the flowers (Photo One)

This is a plant that is native to Europe and North Africa, but not to the UK. However, it is often used in landscaping and to prevent soil erosion, and so I wonder if it was actually planted deliberately – the wall that it was growing over is about ten feet tall, so short of a rope ladder I had no way of looking over to see what else was going on. As it is, it is just a rather intriguing alien, with those deflated balloons all over it.

As you might have gathered from the flowers, it is a member of the Fabaceae or bean/clover family. In his book on Alien Plants, Clive Stace notes that it’s a plant that is very tolerant of dry conditions (hence its thriving on the artificial scree slope of a railway embankment), and indeed Stace says that this is the most likely habitat in which to find this ‘infrequent alien shrub’. If we hadn’t crossed the road to get away from the constant building work that’s taking place in this area, I would never have spotted it. Some of the most wonderful things in life occur though just such happy accidents.

Photo Two by Gailhampshire found at

Some rather more inflated ‘bladders’ (Photo Two)

Apparently, when the pods are dried they become a natural rattle, which has led to them being called ‘wolf-scarer’ in some parts of Portugal and Spain. I’d have thought that wolves were a bit less flighty than that, but who knows?

Bladder senna has a number of cultivated varieties – not surprising when you consider how much it likes tough conditions. Colutea x media, or small bladder-senna, has bright orange flowers, and isn’t actually that small, reaching a height of 3 metres.

Small Bladder-senna (Colutea x media) (Public Domain)

Now, the name senna may provoke memories in older readers – various senna pod preparations were the laxatives of choice prior to some of the gentler alternatives that are available these days. However, the herbalist John Gerard cautions that ‘our’ plant is not true senna, and he calls it ‘bastard senna’. The plant first made an appearance in the UK in 1568, and was probably imported for medicinal reasons – it does still act as a purgative, but is much milder than ‘real’ senna, and the leaves are also diuretic. However, I read with some alarm that the plant is said to be ‘unreliable medicinally’, and that the seeds are both emetic and toxic. It might be best if we limited our interactions to admiration from a distance, although I am rather intrigued by the notion that the seedpods explode with a gratifying bang if squeezed when at their prime.  I note that in the Victorian Language of Flowers, the Bladder Senna represents ‘frivolous amusement’, so pop away!

Although there are no human edible uses for the plant, it is the foodplant for the caterpillar of the long-tailed blue butterfly (Lampides boeticus), a very rare migrant to the south coast of the UK. In Europe it’s seen as a pest on various bean species, including bladder-senna, in the UK I suspect most entomologists would fall on their knees rejoicing at the very sight of it, especially since caterpillars were spotted in 2013, raising hopes that maybe it will start to breed here rather than merely visiting.

Photo Three by RachidH, from

Long-tailed Blue (Lampides boeticus) (Photo Three)

Now, whilst looking for a poem to cast some light on this plant, I discovered that ‘Senna’ is a form of Old Norse poetry, which involves “an exchange of insults between participants, ranging from the use of expletives to accusing an opponent of moral or sexual impropriety” (thank you Wikipedia). But rather more edifying is this poem by Clive James, written on the death of Formula i1 driver Ayrton Senna, named as the greatest racer who ever lived by his fellow drivers. I remember how upset my Dad, who loved Formula 1, was when Senna died.

Just a few notes: an Armco is a crash barrier. Michael Schumacher was seriously injured in a skiing accident, after a career as a Formula 1 driver (though with a rather more chequered reputation than Senna’s).

See what you think.

Ayrton Senna Killed at Imola by Clive James

Thousands of miles away in Buenos Aires
Juan Manuel Fangio, five times world champion,
Watched Senna hit the Armco and sit still.
The world over, we were all interpreting
The silence. Fangio needed only that first glance
And turned the TV off.
Such stillness was a language,
The signal that the angel had departed.

As I write this now
Schumacher is out walking at his home
On Lake Geneva,
Getting the exercise he just might need
If ever his mind comes back.

Moss when he spun across the grass
At Donington with me beside him looking
As if I had seen my own ghost;
Or Derek Warwick on the autostrada
Driving me down to Monza;
Or Alan Jones in that brutal Lamborghini
In Adelaide when we entertained the crowd
With our brilliant imitation of a champion driving
His panic-stricken friend to hospital …
But now all these faces are from long ago
And even
When Damon, in my dreams, comes back to drive me
Under police escort to the airport in Hungary,
I can’t believe how very young he looks.

Deborah, my elder daughter’s friend,
A magnet for adventurous men,
Was taken to a Grand Prix one weekend.
She got so bored she lay down for a sleep
Beside a pile of tyres.
When she woke up again she couldn’t see.
Her eyes were full of rain.

Photo Credits

Photo One By AnRo0002 – Own work, CC0,

Photo Two by Gailhampshire found at

Photo Three by RachidH, from

3 thoughts on “Wednesday Weed – Bladder Senna

  1. Anne

    Your comment about the seeds exploding reminds me of having tea on the deck at a friend’s home when I nearly jumped out of my skin at the explosive crack near to me, followed by others at irregular intervals. She laughed at my initial surprise for the noise emanated from the wisteria seed pods cracking open of their own accord.

  2. Alittlebitoutoffocus

    Looks like that Long-tailed Blue also migrates to Switzerland (around now), though it doesn’t appear to like altitude. So I’d have to search for it down in the Rhone valley. It would certainly be a good find. 😊


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