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Heliamphora purpurascens
Ptari-tepui is one of the smaller Venezuelan table mountains, with a summit that is strikingly flat and offers almost no shelter. There grows Heliamphora purpurascens, a plant that until 2011 was still treated as a mountain form of Heliamphora heterodoxa and only then received a name of its own. That name refers to the first thing you notice: pitchers that flush deep purple in full sun.
Identification
A rosette of erect pitchers up to about 25 cm tall. Each pitcher is a single leaf grown shut into a funnel with a seam down the front; the wall feels stiff and almost woody, harder than in most of its relatives. About halfway up sits a drainage pore that regulates the water level in the trap — rain rising above it simply runs out. The most conspicuous character stands on the back rim: the nectar spoon here is helmet-shaped, with a broad triangular base, and relative to the pitcher it is larger than in almost any other species of the genus. It is also sharply bent forward, so that it hangs over the opening like a hood. Pitcher colour runs from green in sheltered plants to deep purple or purple-red in plants in the open. The inflorescence is, as throughout the genus, a nodding raceme on a long scape; measurements of the scape and floral parts are not established for this species in accessible literature.
Similar species
The species it was long lumped with is Heliamphora heterodoxa of the Gran Sabana, and that remains the main confusion. The difference lies mostly in the nectar spoon: in heterodoxa it is smaller and not so markedly helmet-shaped, in purpurascens large, broadly set and folded forward. The pitcher wall is also stiffer here and turns far more purple. On Ptari-tepui itself the only other candidate is Heliamphora collina, and that grows hundreds of metres lower, on the south-western foothills at around 1700 to 1825 m, not on the plateau. Elevation is therefore a usable field character for these two. Confusion with Sarracenia is ruled out geographically, and structurally too: Heliamphora has no broad hood, only that one spoon.
The trap and how it works
A pitfall trap that catches insects but largely contracts out the digestion. The plant makes few or no digestive enzymes of its own; bacteria in the pitcher fluid do the work, after which the plant takes up the released nitrogen and phosphorus. The large nectar spoon is the lure: nectar is secreted there, and an insect coming to it stands directly above the opening. The upper part of the inner wall carries downward-pointing hairs that defeat every attempt to walk back up; below that the wall is smooth. The drainage pore halfway up keeps the column of fluid at a constant level, so that persistent rain does not overflow the trap and flush the catch away.
Habitat and ecology
The summit plateau of the table mountain (R4), and here that is a notably bare stage: the top of Ptari-tepui is flat and open, with almost nothing to break wind or rain, and cloud covers the ground for much of the day. The plant grows in waterlogged peaty patches where bog moss and a thin layer of acid peat have gathered (W1); that layer rarely exceeds a hand's breadth. The pattern is characteristic: in the wettest parts the water stands at the surface, and low hummocks of mixed tepui flora rise above it like small islands. On and between those hummocks the species grows. The substrate is extremely poor in nitrogen and phosphorus, and rain continually washes away what little there is. Under those conditions a trap that turns insects into nutrients is not a bonus but the precondition for standing here at all.
Distribution and elevation
Endemic to the summit plateau of Ptari-tepui in Bolívar state, Venezuela, and not known from anywhere else. Known sites lie between about 2400 and 2500 m. Global checklists give Venezuela alone as this species' range. The plateau itself is small, which means the entire range of the species can be walked over in a single day. The genus as a whole is confined to the table mountains of the Guiana Shield — Venezuela, western Guyana and the far north of Brazil — and purpurascens shows how that works: for a bog plant each plateau is as unreachable as an island at sea, and on each plateau evolution therefore goes its own way.
- Recorded (one-degree cells)
Forms and variation
No varieties or subspecies have been described. What you do see in the field is colour variation without a taxonomic name, and here it is pronounced: plants in full wind and full light flush deep purple to purple-red, plants in the lee of a hummock stay green or green with purple margins. That difference is a response to exposure rather than something fixed by inheritance. No natural hybrids have been reported from the plateau, which is to be expected: at this elevation there is no second species of the genus to cross with. The mountain's only other Heliamphora grows hundreds of metres lower and therefore flowers in a different microclimate.
Where and when to see it
Ptari-tepui is reachable only by helicopter or on a multi-day trek and lies within Canaima National Park; in practice every visit is made with a permit and a guide. Once on top, look for the species on the wet parts of the plateau, on and around the low hummocks that rise above the water; do not walk straight through the peaty patches, where the vegetation is thin and recovers slowly. Watch the light rather than the calendar: the purple only comes out properly when the cloud briefly opens, and that is the moment you see the difference between plants in the open and plants in shelter. Do not confuse the species with the plants of the foothills; those belong to a different species.
Conservation status
The species has not been assessed for the IUCN Red List, and there is no CITES listing either: Heliamphora appears in no appendix. What can be said is that the known range is confined to the small summit plateau of a single mountain, which makes any species vulnerable by definition to whatever befalls that one plateau. Against that, the habitat lies within Canaima, a national park and World Heritage site, the plateau cannot be entered without a permit, and the populations on the wet ground are reasonably large. Collection for trade is the risk routinely named for the genus, but plants in cultivation now come almost entirely from seed and tissue culture. The absence of a formal assessment therefore signals a gap in the record rather than a known decline — hardly surprising for a species described only in 2011.
Scientific name
Heliamphora purpurascens | Wistuba, Fleischmann, Nerz & McPherson, 2011
Described by Andreas Wistuba, Andreas Fleischmann, Joachim Nerz and Stewart McPherson in 2011, in “Sarraceniaceae of South America” (Redfern Natural History Productions, Poole). The type area lies in the summit region of Ptari-tepui in Venezuela, at elevations of 2400 to 2500 metres. The species name purpurascens is Latin for "becoming purplish" and refers to the purple colouring the pitchers of this species can take on.
World Checklist of Vascular Plants (WCVP), via Plants of the World Online (POWO), Royal Botanic Gardens, Kew.