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Pinguicula pygmaea
A dwarf with a short life: Pinguicula pygmaea is an annual butterwort of gypsum soils in western Oaxaca, described in 2017. An annual habit is rare in this genus — most butterworts are perennial and bridge the dry season with a winter bud — and combined with the gypsum habitat that makes this one of the more remarkable finds of recent years in the Sierra Madre del Sur.
No photograph of this species under a Creative Commons licence or in the public domain is in the guide yet.
Identification
The species is described as small and annual, growing on gypsum-rich ground. For the exact dimensions of rosette, leaf, scape and flower, for flower colour and for flowering time, we could find no freely available, testable statement from the original description; all those fields have therefore been left empty on the fact card, which is a more honest representation here than a borrowed figure. What is certain: it is a miniature rosette of sticky leaves with the glandular coating that characterises the whole genus, and a plant that completes its entire cycle — germination, growth, flowering, seed set, death — within one rainy season.
Similar species
Among Mexican butterworts the annual habit is the sharpest distinction, but in the field you only see it by following a site across several seasons. More usable are size and habitat: a small butterwort on gypsum in western Oaxaca is almost certainly this species. Other small species of the district, such as the members of section Heterophyllum, form a clear fleshy winter rosette which this species lacks. Mexico's other gypsum-dwelling butterworts do not enter the question either: they grow in the north-east of the country, hundreds of kilometres away.
The trap and how it works
The sticky leaves work as a flypaper trap in the familiar pattern: stalked glands with a clear droplet, sessile glands that release digestive enzymes only on contact with prey, and a leaf margin that bends slowly over the catch. In an annual more hangs on this than in a perennial. Everything caught must be converted within one season into leaf, flowers and seed, because there is no next year. On gypsum, where nitrogen and phosphorus are all but absent, that catch is not a supplement but the engine of the entire cycle.
Habitat and ecology
Gypsum soils in the highlands of western Oaxaca, in the Sierra Madre del Sur. Gypsum is a hard, white, nutrient-poor substrate carrying a flora of its own with many species found nowhere else; in Mexico it is one of the classic engines of speciation. The regime is seasonally dry in the extreme (D4): the plant germinates at the onset of the rains, runs through its whole life in a few months, and in the dry season is present only as seed in the soil. For a more precise picture of elevation and associated vegetation we found no testable source.
Distribution and elevation
Endemic to the Mexican state of Oaxaca, in the west of the state, in the Sierra Madre del Sur — in agreement with the entry in our species list. The gypsum outcrops of western Oaxaca lie as small islands in the landscape, and it is that island character that governs the species' distribution: where there is no gypsum there is no plant. The known range is small. Since the gypsum flora of Oaxaca has only recently come under systematic study — more gypsum-dwelling species have been described from the same country in recent years — further sites may yet be added.
- Native
Forms and variation
No wild varieties have been described. In an annual with a small range, moreover, the variation one sees is hard to interpret: annuals respond strongly to the conditions of the current season, so plants from a wet year look different from those of a dry one without any heritable difference behind it. Until a multi-year series of observations per site exists, naming forms is not defensible. No natural hybrids are reported, and in an annual with a distinct flowering time they are in any case less likely.
Where and when to see it
The window is narrow. Search during the rains, a few weeks after the first showers: before that there is no plant, and afterwards the cycle is over. Go to the open white gypsum slopes and terraces of western Oaxaca and search the bare ground between the gypsum crusts, not the vegetation. Get low and use a hand lens — with a dwarf species the difference between seeing and not seeing is a hand's breadth of distance. Collect nothing: in an annual, every plant you take is next year's seed production removed.
Conservation status
The species has not been assessed for the global IUCN Red List and is not listed in CITES. What is known is the profile of a species carrying every vulnerability trait at once: annual, small, tied to a rare soil type, and discovered only in 2017. Annual plants with a small seed bank are sensitive to a single failed season, and gypsum is quarried in Mexico for the building materials industry. Overgrazing by goats does particular damage on open gypsum slopes. An assessment is missing, but here that is simply because the species has only just entered the literature.
Scientific name
Pinguicula pygmaea | Rivadavia, Read & Fleischmann, 2017
Described by Fernando Rivadavia, E.L. Read and Andreas Fleischmann in 2017, in Phytotaxa 292(3): 279–286, based on material (Rivadavia & Read 1814) collected on 20 November 2003. The type locality lies in the Mexican state of Oaxaca, Santo Domingo Tonalá municipality, along Highway 125 between Huajuapan and Tlacotepec, at 1370 metres altitude. The name "pygmaea" (pygmy) refers to the very small size of this annual species, one of the smallest in the entire genus.
World Checklist of Vascular Plants (WCVP), via Plants of the World Online (POWO), Royal Botanic Gardens, Kew.