The butterworts are a group of carnivorous plants comprising the
genus Pinguicula. Members of this genus use sticky, glandular leaves
to lure, trap, and digest insects in order to supplement the poor
mineral nutrition they obtain from the environments. Of the roughly
80 currently known species, 12 are native to Europe, 9 to North
America, and some in northern Asia. The largest number of species is
in South and Central America.
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
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.
Butterworts can be divided roughly into two main groups based on the
climate in which they grow; each group is the further subdivided
based on morphological characteristics. Although these groups are
not cladistically supported by genetic studies, these groupings are
nonetheless convenient for horticultural purposes.
Tropical butterworts either form somewhat compact winter rosettes
composed of fleshy leaves or retain carnivorous leaves year-round.
Temperate species often form tight buds (called hibernacula)
composed of scale-like leaves during a winter dormancy period.
During this time the roots (with the exception of P. alpina) and
carnivorous leaves wither. Temperate species flower when they form
their summer rosettes while tropical species flower at each rosette
Many butterworts cycle between rosettes composed of carnivorous
and non-carnivorous leaves as the seasons change, so these two
ecological groupings can be further divided according to their
ability to produce different leaves during their growing season. If
the growth in the summer is different in size or shape to that in
the early spring (for temperate species) or in the winter (tropical
species), then plants are considered heterophyllous; whereas uniform
growth identifies a homophyllous species.
This results in four groupings:
Tropical butterworts: species which do not undergo a winter
dormancy but continue to alternately bloom and form rosettes.
Heterophyllous tropical species: species that alternate between
rosettes of carnivorous leaves during the warm season and compact
rosettes of fleshy non-carnivorous leaves during the cool season.
Examples include P. moranensis, P. gypsicola, and P. laxifolia.
Homophyllous tropical species: these species produce rosettes of
carnivorous leaves of roughly uniform size throughout the year, such
as P. gigantea.
Temperate butterworts: these plants are native to climate zones
with cold winters. They produce a winter-resting bud (hibernacula)
during the winter.
Heterophyllous temperate species: species where the vegetative and
generative rosettes differ in shape and/or size, as seen in P. lutea
and P. lusitanica.
Homophyllous temperate species: the vegetative and generative
rosettes appear identical, as exhibited by P. alpina, P. grandiflora,
and P. vulgaris.
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
Vector graphic of the trapping and digestive features of a
Like all members of the family Lentibulariaceae, butterworts are
carnivorous. 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 mucilagenous
secretion which forms visible droplets across the leaf surface. This
wet appearance probably helps lure prey in search of water (a
similar phenomena is observed in the sundews). The droplets secrete
only limited 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 entraped 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
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.
Flower of P. vulgaris
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.
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 a 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.
As well as sexual reproduction by seed, many butterworts can
reproduce asexually by vegetative reproduction. Many members of the
genus form offshoots during or shortly after flowering (e.g. P.
vulgaris), which grow into new genetically identical adults. A few
other species form new offshoots using stolons (e.g. P. calyptrata,
P. vallisnerifolia) while others form plantlets at the leaf margins
(e.g. P. heterophylla, P. primuliflora).
Butterworts are distributed throughout the northern hemisphere
(map). The greatest concentration of species, however, is in humid
mountainous regions of Central America (including Mexico) and South
America, where populations can be found as far south as Tierra del
Fuego. Australia is the only continent without any native
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 the United
States include P. caerulea, P.ionantha, P. lutea, P. macroceras, P.
planifolia, P. primuliflora, P. pumila, and P. villosa.
In general, butterworts grow in nutrient poor, alkaline soils. Some
species have adapted to other soil types, such as acidic peat bogs
(ex. P. vulgaris, P. calyptrata, P. lusitanica), soils composed of
pure gypsum (P. gypsicola and other Mexican species), or even
vertical rock walls (P. ramosa, P. vallisnerifolia, and most of the
Mexican species). A few species are epiphytes (P. casabitoana,P.
hemiepiphytica, P. lignicola). Many of the Mexican species commonly
grow on mossy banks, rock, and roadsides in oak-pine forests.
Pinguicula macroceras ssp. nortensis has even been observed growing
on hanging dead grasses. Each of these environments is very
nutrient-poor, allowing butterworts to compete for space.
Butterworts need habitats that are almost constantly moist or
wet, at least during their carnivorous growth stage. Many Mexican
species lose their carnivorous leaves, and sprout succulent leaves,
or die back to onion-like "bulbs" to survive the winter drought, at
which point they can survive in bone-dry conditions. The moisture
they need for growing can be supplied by either a high groundwater
table, or by high humidity or high precipitation. Unlike many other
carnivorous plants that require sunny locations, many butterworts
thrive in part-sun or even shady conditions.
The environmental threats faced by various Pinguicula species
depend on their location and on how widespread their distribution
is. Most endangered are the species which are endemic to small
areas, such as P. ramosa, P. casabitoana, and P. fiorii. These
populations are threatened primarily by habitat destruction. Wetland
destruction has threatened several US species. Most of these are
federally listed as either threatened or endangered, and P. ionantha
is listed on CITES appendix I, giving it additional protection.
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).