Pinguicula ehlersiae — Vorstman's Guide to the Carnivorous Plants

Identification

A low, flat to slightly domed rosette of thick spathulate leaflets, grey-green flushed red-purple, often with a pale mark on the leaf surface. The winter rosette is compact and nearly glandless; the summer rosette is flatter and broader, with a thin but distinct glandular coating. Flowers come from the winter rosette, on a slender scape standing well above the plant. The corolla is pink to violet-purple with a paler throat, and the narrow spur is characteristically hooked at the end. Like its relatives, the plant readily sheds leaflets from which new rosettes grow, so a site often consists of dense cushions of dozens of plants. Notably, flowering takes place while the plant is still in its drought form: the scape rises from a rosette that at that moment barely catches anything and so lives entirely on stored reserves. Only weeks later, with the first rains, does the carnivorous summer rosette appear.

Similar species

The closest relative is Pinguicula esseriana, of which some authors treat P. ehlersiae as a variety. The difference lies in the somewhat flatter rosette, the pale mark on the leaf and the hooked spur; out of flower the two are barely separable in the field. P. debbertiana, from the same gypsum country, also comes into question: it has a smaller flower with a shorter, straighter spur. The literature is openly uncertain here, and on some hills there are plants falling exactly between the three.

The trap and how it works

A flypaper trap with a strong seasonal pattern. On the summer rosette the leaves carry stalked glands with a sticky droplet and, between them, sessile glands releasing digestive enzymes once prey is lying there; the leaf margin then rolls inward a little so the fluid stands. On the winter rosette the leaves are thick, fleshy and almost glandless: that is not a catching organ but a water store for the dry months. Prey is small — springtails, midges, small flies and ants moving over the gypsum in the cool morning hours.

Habitat and ecology

Gypsum soils in dry, semi-desert hills, usually in the lee of shrubs, agaves and hechtias, or on north-facing slopes where the sun strikes less hard (R2, D4). The species occurs between about twelve hundred and sixteen hundred and fifty metres, on the transition from the tableland to the foothills of the Sierra Madre Oriental. Summer rains are short and heavy; for the rest of the year night dew supplies most of the water. Gypsum is a soil few plants can handle, and that keeps competition at a distance. Dew at this site is not incidental but the chief water supply outside the rainy season: on clear nights the gypsum surface cools sharply and enough moisture condenses on it to carry the rosettes through months without rain.

Distribution and elevation

A Mexican endemic, with sites in San Luis Potosí — around Guadalcázar, Santa Gertrudis, El Huizache and Ascensión among others — and in northern Hidalgo, north of Ixmiquilpan and near Tolantongo. Our species list names San Luis Potosí, which matches the centre of the distribution; the Hidalgo populations belong to it as well. The range is small and strongly fragmented, since it follows the gypsum deposits of this dry part of central Mexico.

Recorded (one-degree cells)

Distribution based solely on records at GBIF (Global Biodiversity Information Facility), not on TDWG regions — those are often far larger than the actual range. The light halo is the area around a record, the dark core the record itself. The darker cells are 3 one-degree squares — roughly a hundred and ten kilometres — in which the species has been recorded, from all GBIF records. This is coarser than for most species because hardly any record of this plant carries an accurate coordinate: the locality of poached species is obscured at source. At this scale that obscuring disappears into the noise. The cells show where it has been seen, not where it occurs: an empty square means nothing.

Forms and variation

Flower colour clearly differs between populations, from pale pink to saturated violet-purple, and the curvature of the spur is not equally pronounced in all plants. That variation is gradual, and it is precisely why the species boundary with P. esseriana has remained unclear. No wild varieties are distinguished. How far the rosette reddens depends strongly on exposure and is not a taxonomic character. Where two gypsum-dwelling butterworts grow on the same hill, intermediates should first be considered natural hybrids.

Where and when to see it

Flowering falls at the end of the dry season, from February into April, and that is also the best time to search: the flowers then stand out as pink dots above the pale gypsum while the rosettes themselves are still small. Look on north- and east-facing slopes, at the foot of gypsum banks, and under the edge of shrubs where a little grit gathers. The plants are smaller than a coin; sit down and work through a square metre systematically rather than walking a slope.

Conservation status

Not assessed for the global IUCN Red List, and not listed in CITES. What is known: the species is bound to gypsum, comes from a limited number of areas in two states, and can stand locally in large numbers where conditions suit. Pressure comes from gypsum quarrying, road building and grazing; on top of that, collectors have taken this small, easy species for decades, though cultivated material is now available everywhere. Population figures are unpublished. As long as the species boundary with P. esseriana stays unclear, an assessment is difficult too: first it must be settled where the species begins and ends.

Scientific name

Pinguicula ehlersiae | Speta & Fuchs, 1982

Described by Franz Speta and Franz Fuchs in 1982, in “Neue Pinguicula-Arten (Lentibulariaceae) aus Mexiko”, Stapfia 10: 111–119. The type area lies near Guadalcázar, in the Mexican state of San Luis Potosí; the type material was collected in 1979 by Renate Ehlers. The species name ehlersiae honours Renate Ehlers, who collected the type material.

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