Pinguicula sehuensis — Vorstman's Guide to the Carnivorous Plants

Identification

A rosette of yellow-green leaves with a glistening glandular coat that feels greasy and a margin curled upward; on a steep wall the leaves are held obliquely. Glabrous scapes rise from the centre, each with one two-lipped flower, blue to violet or pale blue, with a two-lobed upper lip, a three-lobed lower lip and a spur. Reliable measurements for plant, corolla and spur could not be traced to a checkable source for this guide and are therefore not given. The chromosome number of sixteen is remarkably low for the genus.

Similar species

On Sardinia itself there is no second butterwort, so confusion in the field is ruled out. The comparison that matters is with Corsican Pinguicula corsica on the neighbouring island and with the mainland species P. vulgaris and P. leptoceras; all of those are polyploid while this species is diploid. That difference cannot be seen with the naked eye but is why the species was described as a distinct taxon, and it makes the plant interesting as a likely parent in the origin of the other Mediterranean butterworts.

The trap and how it works

A flypaper trap that, on an island of long hot summers, works only while there is water. The leaf bears stalked glands with an adhesive droplet and sessile glands releasing digestive enzymes once prey is lying on them. Midges, gnats and springtails from the humid air along the wet rock face make up the catch. After a catch the leaf margin rolls slowly over it so the digestive fluid stands in a shallow dish. The plant needs all of it: on bare, flushed limestone the substrate supplies no usable nitrogen.

Habitat and ecology

Wet limestone rock in the uplands of Sardinia's eastern interior: dripping faces, spring mouths and crevices with water seeping through permanently, in shaded cool parts of the landscape. In a Mediterranean island climate with long dry summers such places are scarce and small. The surrounding maquis and oak woods are dry from June into autumn, and only where limestone takes in the winter's water and releases it gradually can a plant like this persist year-round.

Distribution and elevation

Sardinia, in the uplands around Seui in the province of Ogliastra, where the species was discovered; the range is small and confined to that hill country. Our own species list gives 'Italy' for this taxon; administratively correct but geographically misleading, since this is not a peninsular plant but an island endemic, and the nearest relative on Corsica belongs to a different species. Sardinia and Corsica each have their own butterwort, and the two are not each other's closest relatives.

Native

Distribution by region of the TDWG scheme (World Geographical Scheme for Recording Plant Distributions), from the World Checklist of Vascular Plants — the data behind Plants of the World Online. The map shows the natural range only; where the species has naturalised is given in the text. Within a region the map says nothing about where exactly the plant grows; for threatened species that is deliberate. Outlines: tdwg/wgsrpd. No GBIF records have been gathered for this species yet; once they are, that more precise layer replaces this regional map.

Forms and variation

No wild varieties are recognised. What makes the species special is its ploidy level: with sixteen chromosomes it is the only diploid representative in the Italian group, which otherwise holds counts of thirty-two, forty-eight, sixty-four and even one hundred and twenty-eight. Such doublings are a known engine of speciation in this genus, and a diploid island population then quickly becomes interesting as a possible origin. Within the species, variation in size and flowering follows the wetness of the site.

Where and when to see it

Spring, while winter water is still moving through the limestone and the walls are dripping; in summer the Sardinian interior is too dry and the plant has withdrawn. Search the shaded limestone gorges and the springs of the uplands, and follow the water upward. Look up at the wet faces and use binoculars rather than climbing. This is a small island population: touch nothing, dig nothing up, and record the locality with a photograph and a coordinate no finer than the commune.

Conservation status

The species has not been assessed for the global Red List; there is therefore no international category, and CITES does not apply. In Italian assessments it is listed as vulnerable, which fits the picture: an island endemic with a small range in one hill country, tied to wet limestone sites that are scarce anyway in a Mediterranean climate. The risks are drier summers and declining spring discharge, water abstraction, and trampling or damage to the soft wet sections of wall. Collection is an added risk for a diploid, scientifically interesting species.

Scientific name

Pinguicula sehuensis | Bacchetta, Cannas & Peruzzi, 2014

Described by Gianluigi Bacchetta, Marcello Cannas and Lorenzo Peruzzi in 2014/2015, in the article "A new diploid butterwort species (Pinguicula, Lentibulariaceae) from Sardinia", Phytotaxa 186(5): 279–286. The species is endemic to the Montarbu mountains, near the municipality of Seui, in the Ogliastra region of Sardinia (Italy), where it grows in limestone rock crevices at 1035 to 1185 metres altitude. The name "sehuensis" derives from "Sehu", the Sardinian-language name for the municipality of Seui, where the species was discovered.

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