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Aug 26

Beautiful butterworts

A recent hike in Königssee to see Germany’s highest waterfall was a little underwhelming but the hydrological shortcomings were entirely forgotten when I spotted this beauty growing in a crevice above the lake:

Pinguicula sp. [cc-by-sa-3.0 Steve Cook]: unknown butterwort from German Alps, probably P. vulgaris or P. alpina. Tongue-shaped lime-green leaves form tight rosette, surfaces are covered with sticky mucilage secreted by tiny mucilaginous glands

Unknown butterwort (Pinguicula sp.) in German Alps, probably P. vulgaris or P. alpina.

Butterworts are amongst my favourite carnivorous plants: their murderous ways are so delicately concealed. Who would suspect such a pretty bank of flowers to be a veritable morgue of fungus gnats?

Pinguicula alpina [cc-by-sa-3.0 Steve Cook]: bank of alpine butterworts in flower in Slovenia

Pinguicula alpina in Slovenian Alps

I’ve seen wild butterworts once before (in the Slovenian Alps), where they were obligingly in flower, as you can see above. The two commonest species in the Alps are the white-flowered Pinguicula alpina (alpine butterwort) and the purple-flowered Pinguicula vulgaris (common butterwort): the latter is also found in the UK, but is by no means ‘common’ here. The photo at the top could be either of them, but without the giveaway flowers it’s difficult to tell which.

Pinguicula alpina flower [cc-by-sa-3.0 Steve Cook]: detail of butterwort flower. Flower is white and zygomorphic with five petals, lowermost petal is distinctly hairy and throat of flower leading to nectar tube is yellow

Pinguicula alpina, detail of butterwort flower

Like many carnivorous plants using the’ flypaper’ trapping mechanism, butterworts hold their flowers at some distance from their leaves: the usual explanation for this is that it helps the plant to avoid accidentally capturing its pollinators, but I can find no proper data that support this. The butterworts’ pollinators are evidently fairly large: probably butterflies with long tongues, judging by the very long nectar tube, which you can see in the image of one of the other native UK species (Pinguicula grandiflora) below:

Pinguicula grandiflora flowers [cc-by-sa-3.0 Alex Lomas]: flowers are purple, each has a nectar tube about 15 mm long projecting from the back of the flower

Each Pinguicula grandiflora flower has a nectar tube about 15 mm long projecting from the back of the flower

Butterflies don’t strike me as likely to end up as accidental prey, considering the usual prey is extremely small (about 1 mm) flies:

Pinguicula moranesis drowning a gnat [cc-by-sa-3.0 Steve Cook]: fungus gnat trapped in mucilage secreted by stalked glands covering the leaf surface

Death by butterwort

It’d be pretty easy to design an experiment to investigate this properly, perhaps with the cape sundew Drosera capensis or Alice sundew  Drosera aliciae which are not closely related, but which use a similar trapping mechanism. If you’d be interested, let me know!

Pinguicula moranesis glands [cc-by-sa-3.0 Steve Cook]: microscopic stalked glands covering the leaf surface secrete mucilage

Mucilage glands of Pinguicula moranesis (Mexican butterwort)

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