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Pinguicula caudata
Of all the names in this guide, this is the awkward one. Pinguicula caudata was described by Schlechtendal in 1846, then grew into a catch-all for nearly every large-flowered Mexican butterwort, was sunk by Casper in 1966 as a synonym of P. moranensis, and today stands again as an accepted species in the international checklists. What that species actually is in the field remains unanswered — and saying so plainly is more useful here than a description that would imply a certainty that does not exist.
No photograph of this species under a Creative Commons licence or in the public domain is in the guide yet.
Identification
There is no modern, generally accepted description of this species in the strict sense, and for that reason every measurement and colour field on the fact card has been left empty. What can be said about the name is this: it refers to a plant of the large-flowered Mexican complex around Pinguicula moranensis — a flat rosette of broad sticky summer leaves, a more compact winter rosette in the dry season, and one to several erect scapes carrying a large two-lipped purple-pink flower whose spur is strikingly long and slender. The epithet, 'tailed', refers to exactly that long spur. Anyone who meets a large purple-flowered rosette with a long spur in Mexico has a plant of this complex; the certainty goes no further.
Similar species
The whole question is one of similar species. Pinguicula moranensis is the large variable centre of the complex and the plant with which P. caudata was merged by Casper; section Orcheosanthus further holds species such as P. orchidioides, P. zecheri, P. michoacana and P. oblongiloba, each departing from the average in flower shape, spur length or winter form. Practical advice for the field-guide reader: name a plant of this complex by its site and by measurable characters — spur length, shape of the corolla lobes, nature of the winter rosette — and be sparing with the name caudata as long as its circumscription is unsettled.
The trap and how it works
About the trapping there is no uncertainty: every member of this complex uses the same active flypaper. The summer leaves carry stalked glands on their upper surface exuding a clear viscous droplet, and between them sessile glands that release digestive enzymes only once something is lying on them. Small insects landing on the glistening blade stick fast; their struggling brings more glands into contact and starts a slow growth response in which the leaf margin bends over the prey and holds the fluid in a shallow dish. The winter rosette, made of thick and virtually glandless leaves, does not feed and serves only to see the plant through the dry months.
Habitat and ecology
Plants of this complex grow in the Mexican highlands on damp, half-shaded sites with little soil: mossy banks and earth faces along mountain roads, dripping rock feet and cuttings (R1), and clearings and margins in pine-oak woodland (B5). Characteristic is the combination of ample light and a substrate that saturates after every shower but never stands in water. That is exactly why species of this complex are so often seen along roads: the verge cutting is an artificial version of their natural site. For P. caudata in the strict sense no habitat description of its own is available.
Distribution and elevation
Caution is needed here too. The name was based in the nineteenth century on material from Mexico and was then applied so broadly that distribution statements from that period say little: they refer in effect to the whole complex, which ranges from northern Mexico into Central America. Our species list gives Nuevo León for this name, but we have not been able to confirm that in the literature; it probably derives from cultivated material circulating under the name. Until a modern revision recircumscribes the species and fixes a type, we keep to: Mexican highlands, precise distribution unknown.
Forms and variation
No wild varieties of this species have been described, and logically so: as long as the species itself is not circumscribed, nothing can be distinguished within it. There is, however, a great deal of variation in the complex to which the name belongs, and that is the heart of the problem — it was that variation which led Hemsley in the nineteenth century to lump everything under one name, and Casper to merge them again in 1966. Countless clones circulate in the plant trade under the name caudata, often with a fancy name attached; they have no place in this guide, because they are not forms distinguished in the wild.
Where and when to see it
The best contribution a field observer can make here is not an identification but documentation. If you meet a large-flowered butterwort with a long spur in the Mexican highlands, photograph the flower from the front and from the side with the spur length visible, the summer rosette from above, and if possible the winter rosette in the dry season, and record altitude and habitat precisely. Observations of that kind — with place, date and measurable characters — are exactly what a future revision of this complex needs. Do not identify by the name of a cultivated clone, and leave plants where they are: wild-collected specimens do not advance the question.
Conservation status
The species has not been assessed for the global IUCN Red List and is not listed in CITES. In this case that is unavoidable: a taxon that is not sharply circumscribed cannot meaningfully be assessed for threat, because it is unclear which populations one would count. What is known applies to the complex as a whole: the large-flowered Mexican butterworts almost all grow on road cuttings and rock faces in mountain forests that are declining through logging, conversion and road works, and they are collected from the wild on a large scale for the trade. For this name, though, the first need is taxonomic: clarity about what the species is, before anything can be said about how it fares.
Scientific name
Pinguicula caudata | Schlechtendal, 1832
Described by Diederich Franz Leonhard von Schlechtendal in 1832. The species occurs in Mexico. The species name caudata is Latin for "tailed" and refers to a tail-like appendage on the flower.
World Checklist of Vascular Plants (WCVP), via Plants of the World Online (POWO), Royal Botanic Gardens, Kew.