The Carnivorous Plant FAQ v. 12

Q: Pinguicula: the butterworts

A: Pinguicula is a genus of most-uncarnivorous-looking, yet quite carnivorous plants. The basic architectural plan of most species in the genus is that of a little ground-hugging rosette of succulent leaves. Often the leaves have a glossy, pearly, opalescent character to them. Flowers--often spectacularly pretty--are produced from the center of the rosette, and nod singly from the top of tall, tender stalks. How can this sweet little thing be a carnivore?

Their arthropodicidal nature becomes clear only when you look very closely at the leaves. For there, adhering to the glandular surface of the leaf, are countless tiny little gnats and other minute arthropods. They are not only stuck to the leaf---they are drowned in moist pools of slime, and are indeed being digested. How horrible!

The details are terrifying. The leaves sometimes emit a faintly fungal scent, perhaps to attract prey. The leaf surfaces have two types of glands: stalked and sessile. The stalked glands are always ready to capture prey, by means of the sticky droplet of goo that sits on its top. The stalked gland sits on top of a reservoir cell that is filled with digestive enzymes. When stimulated, the reservoir cell dumps its contents through the stalked gland, covering the captured prey. This does not happen fast enough to help capture the prey, but it does improve the digestion. The sessile glands also release fluid that is loaded with digestive enzymes, possibly doing the bulk of the digestion. The reservoir cells in the sessile glands do not recharge---once they exude their digestive fluids, they are no longer operative.

Using this powerful set of tools, these plants often manage to capture surprisingly large prey--I have seen plants in the wild covered with large flies (nearly 1 cm in length) or even craneflies (Tipulidae).

For the most part, there is no motion in the leaves. However, the leaves do often dimple slightly underneath captured prey, possibly to create a little pool of fluid to aid in digestion. Also, and especially on temperate species, the leaves roll up on the edges. A few theories have been proposed to explain this, and perhaps two of the most intriguing are that the leaves may be curling up to keep marauding ants from stealing the captured prey, or to create a kind of tubelike structure along the edges of the leaves so that capillary action spreads the nutrient-rich bug juices over a larger amount of leaf area, enhancing nutrient absorption.

Since their traps are fairly generalistic in nature, Pinguicula plants run the risk of capturing their pollinators, which would not be in its best interests. So, the plants produce flowers with bright colors and nutritious nectar that attract insects (and even hummingbirds). These creatures pollinate the flowers in safety. Meanwhile, the deadly leaves of the plant are closer to the ground (where pollinators are less likely to venture), and are perfumed with a fungal, musty smell that is not attractive to the pollinators, although gnats find the funk from the leaves to be irresistible.

Because of their somewhat slimy leaves, the plants were given the name Pinguicula by Linnaeus, which translates to "little greasy one." Coincidentally, I had a similar nickname in gradeschool. The most frequently used common name for this plant in English is "butterwort", although aficionados of the genus affectionately call them "pings." (That is the name you should use if you want to sound cool, like you have been growing the plants for a million years.)

As I describe elsewhere in the FAQ, there are a few recorded enthobotanical uses for European Pinguicula species, especially ones related to curdling milk. There are also magical uses for Pinguicula that I have never tried, as I never have had to inspire visions of what my future husband might look like (especially as such revelations might concern my wife).

The centers of species diversity for Pinguicula are Mexico, Cuba, southeastern USA, and northern Europe. In the next set of pages I will describe the major groups of species, using a system that partially follows these regions and that pays attention to the subgenus divisions as currently understood. After I describe the various species, I'll finish with cultivation and conservation comments.

Page citations: Alm, T. 2005; Casper, J. 1966; Legendre, L. 2000; Rice, B. 2006a; Schlauer, J. 2002; Studnicka, M. 2001.

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Revised: 2018
©Barry Rice, 2018