Butterwort is a carnivorous plant native to Mexico and central America where they grow on mossy limestone rocks and exposed outcrops. Their natural habitat also follows an annual wet and dry season, so many of the species have distinct growth and dormancy cycles, but regardless of season, their care is the same.
I. Appearance and Characteristics
Pinguicula, commonly known as butterworts, is a genus of carnivorous flowering plants in the family Lentibulariaceae.
The name Pinguicula is derived from a term coined by Conrad Gesner, who in his 1561 work entitled Horti Germaniae commented on the glistening leaves: “propter pinguia et tenera folia…” (Latin pinguis, “fat”). The common name “butterwort” reflects this characteristic.
Butterworts are distributed throughout the northern hemisphere (map). The greatest concentration of species, however, is in humid mountainous regions of Mexico, Central America and South America, where populations can be found as far south as Tierra del Fuego. Australia and Antarctica are the only continents without any native butterworts.
Butterworts probably originated in Central America, as this is the center of Pinguicula diversity – roughly 50% of butterwort species are found here.
The great majority of individual Pinguicula species have a very limited distribution. The two butterwort species with the widest distribution – P. alpina and P. vulgaris – are found throughout much of Europe and North America. Other species found in North America include P. caerulea, P. ionantha, P. lutea, P. macroceras, P. planifolia, P. primuliflora, P. pumila, and P. villosa.
The majority of Pinguicula are perennial plants. The only known annuals are P. sharpii, P. takakii, P. crenatiloba, and P. pumila. All species form stemless rosettes.
- Roots
The root system of Pinguicula species is relatively undeveloped. The thin, white roots serve mainly as an anchor for the plant and to absorb moisture (nutrients are absorbed through carnivory). In temperate species these roots wither (except in P. alpina) when the hibernaculum is formed. In the few epiphytic species (such as P. lignicola), the roots form anchoring suction cups.
- Leaves and carnivory
The leaf blade of a butterwort is smooth, rigid, and succulent, usually bright green or pinkish in colour. Depending on species, the leaves are between 2 and 30 cm (1-12″) long. The leaf shape depends on the species, but is usually roughly obovate, spatulate, or linear. They can also appear yellow in color with a soft feel and a greasy consistency to the leaves.
Like all members of the family Lentibulariaceae, butterworts are carnivorous. The mechanistic actions that these plants use to lure and capture prey is through a means of sticky or adhesives substances that are produced by mucilage secreted by glands located on the leaf’s surface. In order to catch and digest insects, the leaf of a butterwort uses two specialized glands which are scattered across the leaf surface (usually only on the upper surface, with the exception of P. gigantea and P. longifolia ssp. longifolia).
One is termed a peduncular gland, and consists of a few secretory cells on top of a single stalk cell. These cells produce a mucilaginous secretion which forms visible droplets across the leaf surface. This wet appearance probably helps lure prey in search of water (a similar phenomenon is observed in the sundews). The droplets secrete limited amounts of digestive enzymes, and serve mainly to entrap insects.
On contact with an insect, the peduncular glands release additional mucilage from special reservoir cells located at the base of their stalks. The insect will begin to struggle, triggering more glands and encasing itself in mucilage. Some species can bend their leaf edges slightly by thigmotropism, bringing additional glands into contact with the trapped insect.
The second type of gland found on butterwort leaves are sessile glands which lie flat on the leaf surface. Once the prey is entrapped by the peduncular glands and digestion begins, the initial flow of nitrogen triggers enzyme release by the sessile glands. These enzymes, which include amylase, esterase, phosphatase, protease, and ribonuclease break down the digestible components of the insect body. These fluids are then absorbed back into the leaf surface through cuticular holes, leaving only the chitin exoskeleton of the larger insects on the leaf surface.
The holes in the cuticle which allow for this digestive mechanism also pose a challenge for the plant, since they serve as breaks in the cuticle (waxy layer) that protects the plant from desiccation. As a result, most butterworts live in humid environments.
Butterworts are usually only able to trap small insects and those with large wing surfaces. They can also digest pollen which lands on their leaf surface. The secretory system can only function a single time, so that a particular area of the leaf surface can only be used to digest insects once.
Unlike many other carnivorous plant species, butterworts do not appear to use jasmonates as a control system to switch on the production of digestive enzymes. Jasmonates are involved in the butterwort’s defense against attacking insects, but not in its response to prey. Of the eight enzymes identified in the digestive secretions of butterworts, alpha-amylase appears to be unique when compared to other carnivorous plants. This research suggests that butterwort may have co-opted a different set of genes in its development of carnivory.
Flowers
As with almost all carnivorous plants, the flowers of butterworts are held far above the rest of the plant by a long stalk, in order to reduce the probability of trapping potential pollinators. The single, long-lasting flowers are zygomorphic, with two lower lip petals characteristic of the bladderwort family, and a spur extending from the back of the flower.
The calyx has five sepals, and the petals are arranged in a two-part lower lip and a three-part upper lip. Most butterwort flowers are blue, violet or white, often suffused with a yellow, greenish or reddish tint. P. laueana and the newly described P. caryophyllacea are unique in having strikingly red flowers. Butterworts are often cultivated and hybridized primarily for their flowers.
The shape and colors of butterwort flowers are distinguishing characteristics which are used to divide the genus into subgenera and to distinguish individual species from one another.
- Fruit and seed
The round to egg-shaped seed capsules open when dry into two halves, exposing numerous small (0.5–1 mm), brown seeds. If moisture is present the silique closes, protecting the seed and opening again upon dryness to allow for wind dispersal. Many species have a net-like pattern on their seed surface to allow them to land on water surfaces without sinking, since many non-epiphytic butterworts grow near water sources. The haploid chromosome number of butterworts is either n = 8 or n = 11 (or a multiple thereof), depending on species. The exception is P. lusitanica, whose chromosome count is n = 6.
II. How to Grow and Care
Sunlight
Pings do well with moderately-bright light. Near an East or west window where they get direct sun for the early or late hours of the day. Direct sun in midday may be too hot and could scorch the leaves.
They also do very well under LED grow lights where the light intensity is more consistent throughout the day. If you’re using LED lights, opt for about 18-24w of LED light per square foot at about 12″ from the light. If the plants are closer to the light, opt for lower wattage (12-18w); and if they’re further, opt for higher wattage because you’ll lose light intensity to dispersion.
Water Quality & Watering
Don’t use tap water. Like most carnivorous plants, pings do best with pure water that isn’t going to burn the roots or cause issues as the water evaporates. If your water is high in minerals, those salts can/will concentrate over time as you water and the water evaporates—this can lead to conditions that pings just aren’t able to mitigate. For my plants, I use bottled water (Aquafina or SmartWater), but you can use any brand that has less than 20 ppms. Typically, water bottles will say the total ppms (which means parts per million or 1mg per 1L of water) and as close to 0 you can get is ideal. Distilled or RO water will also work—it’s pure water without minerals.
Don’t water the rosettes from above: or rather, avoid showering pings from above and allowing water to collect on the leaves. It can be done, and I have done it a few times to clean leaves which have accrued lots of dead bugs. However, smaller plants tend to be more susceptible to leaf and crown rot if water pools and stays in the rosette and any time I’ve done a “top-down shower”, I’ve lost at least one or two small seedlings. Instead either water from the bottom or water around the rosettes using a water bottle that has a single hole melted in the lid – this will allow you to target moisten around the plant without actually getting water all over the leaves.
Fertilizing
Don’t use chemical fertilizers—opt for insects. If you don’t have a fungus gnat problem (like I clearly do), then lucky you! You can still generally get away with not having to feed your plant as the bulk of the “food” comes from light. Pings will feed off tiny soil insects (like mites, springtails, etc) and things that are naturally already in your pots—this is why they make good companions for people who already have a lot of plants!
Propagation
There are three ways to propagate butterworts: by vegetative cloning with “leaf pullings”, by division, or by seed. All three are fairly easy to do; however, leaf pullings tend to grow a little faster than seedlings and divisions of the plant should only be taken in late spring after flowering is complete and the plants have naturally split into multiple new rosettes. Be aware: seed-produced plants will have more variability than the cloned leaf pullings (which would be identical to the parent plant they came from).
- Dividing
When pings are very happy and established, they will flower in the spring and at the same time, with the new buds, the rosette will often split into 2 or more new rosettes. After flowering is complete, and as the rosettes start to produce their own set of leaves, you can simply unpot and divide them. I have learned the hard way that if you do this too early…you can pull all the leaves off a rosette and not divide the plant at all. It may be better to use a sharp knife and cut the pup away from the main mother but make sure it’s big enough to do so. These divisions will be clones of the parent plant and will be identical to your original butterwort.
- Leaf Pullings – Ping Clones
If you’ve ever propagated succulents via leaf pullings, this is exactly the same process. The best time to take a leaf pulling from your ping is at the end of their dormancy, just before or as new leaves are being produced for the growing season. The leaves will be succulent and easy to detach. That said, if your plant is healthy and established, you should be able to take pullings anytime of year.
To propagate from a leaf pulling: Take an old leaf from the outter-edge of the rosette, pull it down and away from the plant so that it snaps off (as close to the base as possible). Place the leaf sticky-side up on the surface of the potting media and leave it until a new plant grows which is large enough to sustain itself. That’s it – then you can grow it out and share with friends.
How to Pollinate
Pings have pretty neat looking flowers, but if it’s your first time seeing one, you might have a hard time figuring out where the pollen or stigma are (the stigma is the spot where the pollen needs to be placed in order to fertilize the ovary and make seeds). I’ll include a photo to illustrate the process but here are the basic steps:
- Pull the flower apart (grasp the top two petals and the bottom three petals separately and slowly pull). Expose the reproductive bits. Sorry, I know it’s sad to hurt the flower—do this gently, as you don’t want to pull the reproductive parts off the plant.
- Get a toothpick and color the tip with a sharpie so you can see the pollen. Let the marker on the toothpick dry before using.
- Look at the flower and you’ll see a little flat thing with two little hook-like hangy things below it. The flat part is the stigmatic surface, and directly underneath it is where the pollen is. You’ll need to take the toothpick, gently lift the stigma and put the toothpick inside like you’re scooping a mini treasure out of a tiny treasure box.
III. Uses and Benefits
Butterworts are widely cultivated by carnivorous plant enthusiasts. The temperate species and many of the Mexican butterworts are relatively easy to grow and have therefore gained relative popularity. Two of the most widely grown plants are the hybrid cultivars Pinguicula × ‘Sethos’ and Pinguicula × ‘Weser’. Both are crosses of Pinguicula ehlersiae and Pinguicula moranensis, and are employed by commercial orchid nurseries to combat pests.
Butterworts also produce a strong bactericide which prevents insects from rotting while they are being digested. According to Linnaeus, this property has long been known by northern Europeans, who applied butterwort leaves to the sores of cattle to promote healing. Additionally, butterwort leaves were used to curdle milk and form a buttermilk-like fermented milk product called filmjölk (Sweden) and tjukkmjølk (Norway).
