Pinguicula nivalis

No photograph of this species under a Creative Commons licence or in the public domain is in the guide yet.

Identification

For the dimensions of rosette, leaf and scape we could not trace a testable statement from the original description, so those fields have been left empty on the fact card. What is on record are the floral characters on which the species was distinguished. The flower is white, with a yellow patch in the throat surrounded by conspicuously long and numerous white hairs — in the closely related Pinguicula immaculata those hairs are shorter and sparser. The spur of P. nivalis is shorter and stouter than in that species. For the rest the plant behaves as a typical Mexican butterwort with two guises: non-carnivorous fleshy leaves during the dry winter rest, and thin sticky trapping leaves in the growing season.

Similar species

The comparison runs within a small company: section Microphyllum, which besides this species holds Pinguicula immaculata and P. gracilis, all three small white-flowered gypsum dwellers of north-eastern Mexico. P. immaculata is the direct counterpart; the distinction lies in the throat hairs (longer and more numerous in P. nivalis) and in the spur (shorter and stouter). These are fine characters calling for a good photograph from the front and from the side. The large purple-flowered butterworts of the Sierra Madre Oriental are separable from this group at a distance.

The trap and how it works

The sticky summer leaves form a flypaper trap of the usual design: stalked glands with a clear droplet, sessile glands that release enzymes only on contact with prey, and a margin that bends slowly over the catch. In a gypsum landscape this is a neat solution to a real problem. Gypsum supplies calcium and sulphate in abundance but almost no nitrogen or phosphorus, and plants growing on it must find those elsewhere. For a butterwort that means: from the insects. Here the catch is mostly the small dusty flies and ants that move over the open gypsum ground.

Habitat and ecology

A slope of nearly pure gypsum at about 1425 m, on the north-facing side — precisely the aspect that gets least sun and therefore holds most residual moisture. The vegetation is open and low; gypsum soils are hard, white and nutrient-poor and carry their own highly specialised flora in which many species occur nowhere else. The regime is markedly seasonal (D4): the rain falls in the summer months and the plant grows, after which the slope dries out completely for months and it withdraws into fleshy, non-carnivorous leaves. Limestone plays no part here; this is gypsum, a quite different rock with a quite different chemistry.

Distribution and elevation

Endemic to Mexico, in the south of the state of Nuevo León, near Zaragoza — in agreement with the entry in our species list. The species is described as a gypsophilous endemic of that area. The gypsum outcrops of north-eastern Mexico lie scattered through the landscape like islands, and each island may hold its own species; that is why several new butterworts have been described from this district in a short span of years. As far as known, the range of this species is confined to one or a few of those gypsum hills.

• Native

Forms and variation

No wild varieties have been described. In a species known only from one or a few gypsum hills there is no basis for them: the environment is uniform across the range and there are no separate populations in differing conditions to compare. Such variation as exists concerns chiefly plant size — on the barest, sunniest gypsum they stay smaller — and the extent of the yellow throat patch. No natural hybrids are reported; the related gypsum dwellers occupy their own, mutually separated gypsum islands.

Where and when to see it

Search during the summer months, once the rain has come and the plants carry their trapping leaves; in the dry season almost nothing of the rosette is left. Go to the north-facing sides of gypsum hills: the south side is too hot and too dry. Against the white, hard gypsum the green rosettes stand out well — this is one of the few Mexican butterworts easier to see than to reach. The surface of a gypsum slope is brittle and the crust breaks underfoot; keep to firm paths or the edge of the slope. Photograph the flower from the front and from the side, since throat hairs and spur shape decide the identification.

Conservation status

The species has not been assessed for the global IUCN Red List and is not listed in CITES. What is known fits the pattern of the gypsum butterworts of north-eastern Mexico: a small isolated range on a peculiar soil type, populations limited in area, and a species described only this century. Gypsum is quarried on a fairly large scale in Mexico for construction, and a gypsum hill taken into production disappears entirely. White-flowered Mexican butterworts are also sought after by collectors, and the site lies in an easily reached part of Nuevo León. There is no category because nobody has made the assessment, not because there is nothing to assess.

Scientific name

Pinguicula nivalis | Luhrs & Lampard, 2006

Described by Holger Lührs and John Lampard in 2006, in Carnivorous Plant Newsletter 35(1): 4–9. Alfred Lau had already mentioned the plant in 1998 at an ICPS conference, then suspected to be a population of P. immaculata; a 2004 field expedition by Fernando Rivadavia and colleagues confirmed it was a distinct species. The type locality lies in a gorge near Zaragoza, in the Mexican state of Nuevo León, at approximately 1425 metres altitude, on a gypsum hillside. The name "nivalis" is Latin for "related to snow"; exactly what the authors intended by it could not be established with certainty — it possibly refers to the winter rosette of succulent leaves or to the relatively high, cooler habitat.

World Checklist of Vascular Plants (WCVP), via Plants of the World Online (POWO), Royal Botanic Gardens, Kew.