All species › Lamiales › Bladderwort family › Pinguicula greenwoodii
Pinguicula greenwoodii
A blue-flowered butterwort from a permanently wet cliff face in the cloud forest of Oaxaca, described by Martin Cheek in 1994 and named for Ed Greenwood, the botanist who spent years collecting, photographing and documenting the butterworts of Oaxaca. The type population held more than two hundred plants on a single face — a lot for a Mexican butterwort, and at the same time a statement about the scale at which these species live.
No photograph of this species under a Creative Commons licence or in the public domain is in the guide yet.
Identification
A flat rosette of sticky leaves, as in all Mexican butterworts, with glistening glandular droplets on the upper surface. For the exact dimensions of rosette, leaf and scape we could not obtain a testable statement from the original description, so those fields have been left empty on the fact card. Flower colour, however, is on record: the flowers look blue in the field and were compared in the description with RHS Purple 76B — a remarkably clean blue-purple, in which this species stands apart from most Mexican relatives, which tend towards pink or red-purple. That colour, combined with the habitat on a dripping rock face, is the most usable field character.
Similar species
Several butterworts grow side by side in the cloud forest of Oaxaca: Pinguicula moranensis in its many guises, P. hemiepiphytica, P. laueana with its red flower, and the small species of section Heterophyllum. The blue-purple of P. greenwoodii is unusual in that company; most species here are pink, purple-pink or white. If in doubt, consider the site: this species was described from a continuously wet vertical face, not from a road bank or forest floor. A blue flower on a wet face in the country along the Zacatepec road makes this species the first candidate.
The trap and how it works
The trapping is the genus's active flypaper. Stalked glands on the upper leaf surface carry a clear viscous droplet, and the sessile glands between them release digestive enzymes only once prey is lying there; over the following hours the leaf margin bends slightly over the catch so the fluid pools in a shallow dish. On a permanently wet cloud-forest face the glandular coating never dries out, which means the trap works all year round. The catch is mostly midges, small flies and winged ants, supplemented by whatever drops from the canopy.
Habitat and ecology
A continuously wet vertical rock face in mixed cloud forest at about 1550 m (R1, B1). It is a habitat with no soil of its own: the plants hang in a thin film of moss and algae on the rock, over which water seeps permanently and carries every nutrient away. Such a face is uninhabitable for nearly every other plant, and that is exactly why a carnivorous rosette can dominate it — more than two hundred individuals were counted on the type face. Mist and a closed canopy keep humidity high throughout the year.
Distribution and elevation
Endemic to the Mexican state of Oaxaca, known from the country along the road to Zacatepec at about 1550 m. Oaxaca is by far the richest Mexican state for butterworts and at the same time one of the least explored: many species are known from a single ridge or even a single rock face, and this is one of them. That does not necessarily mean the species is rare everywhere — it mainly means the distribution map reflects search effort rather than reality. Further finds in the surrounding mountains of the Sierra Mixe and the Sierra Sur are quite conceivable.
- Native
Forms and variation
No wild varieties have been described, and with a species known essentially from the type locality nothing else is possible: distinguishing forms requires populations from different environments, and there are none. Such variation as is on record concerns the shade of the blue-purple, which differs noticeably even within one face between plants in full shade and plants in a brighter crevice. Until a second, distant population is found, nothing sensible can be said about geographic forms. No natural hybrids are reported.
Where and when to see it
Look for wet vertical rock faces in cloud forest around fifteen hundred metres and scan them from bottom to top — this species is not on the forest floor but on the face itself, often from chest height well upwards. The blue-purple flower is the most conspicuous thing; the rosettes are green and vanish among mosses and liverworts. Go on a day of mist or light drizzle: the face is then wet, the glands glisten and the plants show best. Do not climb the face and take nothing away: a single rock face can hold the entire known population of a species, and here that is literally true.
Conservation status
The species has not been assessed for the global IUCN Red List and is not listed in CITES. What is known is in this case extremely little: essentially one documented population of some two hundred plants on one rock face, since 1994. Any local intervention — road widening, clearing a slip, diverting a spring, a landslide — can remove such a population at a stroke, and the Oaxacan cloud forest is in general decline through logging and conversion to coffee and pasture. Mexican butterworts with a blue flower are also sought after in the trade. The missing assessment here says only that nobody has done the sum.
Scientific name
Pinguicula greenwoodii | Cheek, 1994
Described by Martin Cheek (Kew) in 1994, in Kew Bulletin 49: 813. The type area lies along the Zacatepec road, in the Mexican state of Oaxaca, at 1550 metres elevation. The species name greenwoodii honours the British botanist Ed Greenwood, who discovered the species during fieldwork in Oaxaca.
World Checklist of Vascular Plants (WCVP), via Plants of the World Online (POWO), Royal Botanic Gardens, Kew.