Teasing Carnivorous Teasels?

Teasel, Dipsacus fullonum, in winter sunshine. © Karen Netto (Andrews)

Teasels are a familiar sight at Christmas. We see them sprayed silver and gold in dried seasonal flower arrangements or crafted into hedgehogs. Teasels’ dense, dry seedheads are surrounded by an eye-catching whorl of bracts. They add interest to largely colourless, winter walks. Their tall structures stand out dramatically at the water’s edge in winter sunshine or silhouetted on drab days. Their seeds feed wild birds in winter and are a particular favourite of Goldfinches. They provide a generous feast for bees in summer months too. Can it really be true that Teasels have carnivorous tendencies and bite back? Or are the scientists teasing us?

Teasels are biennials. They do not flower until their second year. The first year’s teasing signs are a basal rosette of spiky leaves.

Basal rosette of Teasel, Dipsacus fullonum. © Karen Netto (Andrews)

Teasels reach for the sky in their second year. They tower over us, revealing ferocious-looking prickles on stems and the undersides of spear-shaped leaves.

Previous year’s spent Teasels and new growth side by side at Westbury Quarry, Somerset
© Karen Netto (Andrews)

Bees love Teasel flowers in the summer months. Teasels are such great supporters of biodiversity, it is hard to believe that Teasels might have murderous tendencies.

A characteristic feature of the cup-like structure that holds water.

Carnivorous or Protocarnivorous?

The theory that Teasels might have carnivorous tendencies has been around a long time. The idea was first suggested by Francis Darwin, botanist son of the famous naturalist and carnivorous plant-lover Charles Darwin. Might Teasels be getting some benefit from dead insects drowned in its water cup? Or do the cups simply prevent the advance of insects crawling up the stem?

Scientists have taken a while to conduct illuminating experiments on the plant’s behaviour. Scientific experiments need repeatable results before reaching a definitive conclusion. It was thought that the plant might gain additional nitrogen and phosphorous. Papers seem to suggest that Teasel seeds, rather than the plant’s own growth, gain the greater benefit.

There is a difficulty in interpretation. Carnivorous plants do not really have a decisive description. The current terminology sometimes allows for varying degrees of carnivory. A strict definition requires that a carnivorous plant traps, has enzymes and dedicated structures to digest its prey. Such carnivorous plants live in nutrient-poor conditions.

Teasels do not digest trapped insects using enzymes and specialised structures. The cup certainly acts as a pitfall. Is it by chance or design? Some carnivorous plants rely on mutualistic interactions to digest their prey. Teasels do not fall into this camp either.

If it can be argued that the Teasel has carnivorous tendencies based on current research, then it is probably best described as protocarnivorous or paracarnivorous. It may trap and kill insects, but it lacks the ability to complete the deed and digest them. A true carnivorous plant has recognised morphological adaptations.

The Teasel is teasing us into getting to know it better. Time to do a double take on those glittering Teasel decorations?

© Karen Netto (Andrews)

References and Further Reading

Krupa, James J. & Thomas, J. Matthew (2019). Is the Common Teasel (Dipsacus fullonum carnivorous or was Francis Darwin wrong? Canadian Science Publishing via Research Press. 6 June 2019 Botany, 2019, 97(6): 321-328.

Matt (?) (2017): Evidence of Carnivory in Teasel. In Defense of Plants Blog. 20 September 2017. Last accessed online 4 December 2019.

Sandles, Tim (2017): Dartmoor’s Teasels. Legendary Dartmoor. 21 September 2019 Last accessed online 4 December 2019.

Shaw, Peter J. A. & Shackleton, Kyle (2011): Carnivory in the Teasel Dipsacus Fullonum – Experimental Feeding on Growth and Seed Set. PloS One. 2011: 6(3): e17935. Published online March 18 2011. Last accessed online 4 December 2019. Research Gate Article Access

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