butterwort n : any of numerous carnivorous bog plants of the genus Pinguicula having showy purple or yellow or white flowers and a rosette of basal leaves coated with a sticky secretion to trap small insects

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 the rest are found in northern Asia, South and Central America and southern Mexico.

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…" (lat. pinguis = fat). The common name "butterwort" reflects this characteristic.

Characteristics

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.

Habit

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 change.

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.

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.

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. S. J. Casper's large 1966 monograph of the genus included 46 species, a number which has almost doubled since then. Many exciting discoveries have been made in recent years, especially in Mexico. Another important development in the history of butterworts is the formation of the International Pinguicula Study Group, an organization dedicated to furthering the knowledge of this genus and promoting its popularity in cultivation, in the 1990s.

Uses

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.

Classification

For a list of species, see the separate article List of Pinguicula species.

Pinguicula belong to the Bladderwort family (Lentibulariaceae), along with Utricularia and Genlisea. Siegfried Jost Casper systematically divided them into three subgenera with 15 sections.

A detailed study of the phylogenetics of butterworts by Cieslak et al. (2005) found that all of the currently accepted subgenera and many of the sections were polyphyletic. The diagram below gives a more accurate representation of the correct cladogram. Polyphyletic sections are marked with an *.

┌────Clade I (Sections Temnoceras *, Orcheosanthus *, Longitubus, │ Heterophyllum *, Agnata *, Isoloba *, Crassifolia) │ ┌───┤ │ │ │ │ ┌──────┤ └────Clade II (Section Micranthus * = P. alpina) │ │ │ │ ┌───┤ └────────Clade III (Sections Micranthus *, Nana) │ │ │ │ ───┤ └───────────────Clade IV (Section Pinguicula) │ │ └───────────────────Clade V (Sections Isoloba *, Ampullipalatum, Cardiophyllum)

References

Much of the content of this article comes from the equivalent German-language wikipedia article (retrieved March 29, 2006).

Further reading

• Karnivoren

External links

• An exhaustive website on the genus Pinguicula
• Schlauer, J. Carnivorous Plant Database, version 15 November 16: 25.
• Flora Europaea: Pinguicula species list
• Botanical Society of America, Pinguicula - the Butterworts