Based on current floristic literature, Pinguicula involuta was considered as the only butterwort native in northern Peru. However, a revision of the available herbarium material in this study has revealed that this simple assumption, according to the historical taxonomic treatments, P. involuta is native to Peru whilst P. calyptrata is native to Ecuador, is largely incorrect. Furthermore, the “northern” Pinguicula of Humboldt and Bonpland (i.e. P. calyptrata), that was first discovered in the Saraguro range in southern Ecuador, has repeatedly been collected in northern Peru. We have seen specimens of P. calyptrata from the Peruvian Departments Piura, Amazonas, San Martín, Lambayeque and Cajamarca (Fig. 4, cf. the list of specimens below). In turn, P. involuta, so far, has never been collected in these Departments, although misidentified collections and erroneous floristic literature suggest that. Based on our observations and fieldwork, the northernmost locality of P. involuta is in the Department Huánuco in central Peru, some 350 km further south of the southernmost P. calyptrata localities (Province Pachitea, Panao; road from Chaglia [Chaglla] to Rumichaca [Tambo de Vaca], km 81, 09°51'S, 75°53'W), leg. M. Weigend, K. Weigend, T. Henning, & Ch. Schneider 5426, Fig. 4). At present, the exact distribution limits of P. involuta and P. calyptrata remain uncertain.

Morphological data indicate that the new taxon is distinct from P. involuta and P. calyptrata. A thorough study of South American Pinguicula is in preparation and will elucidate the morphological affinities amongst all relevant taxa.

Foliage: The leaf blades of P. rosmarieae are ovate-obovate-oblong, dried membranous-translucent (Fig. 2A) and spread out, i.e. they are not boat-like and they lack heavily curled-up margins (Fig. 1A, E): The whole rosette (up to 100 mm across) is not star-shaped compared to P. calyptrata (Figs 1J, 2C) and P. involuta (field name of the latter in the original collection was P. stellata, see Casper and Hellwig 2019). The foliage shape of P. rosmarieae is similar to the geographically-distant P. albida Wright that occurs in Cuba and may represent an individual adaptation to the rocky, exposed habitats. Both habitats share nutrient-poor and often acidic white-sand-soils (for Peru: M. Weigend, pers. comm.). However, this observation is contradicted by the fact that the rosettes of P. calyptrata and P. involuta retain their star-like appearance on relatively open stands. Shape and posture of the foliage are, therefore, taxonomically meaningful for species delimitation.

Corolla: The violet-white to pale-bluish corolla is similar to that of most Andean Pinguicula: its lips are nearly equal-lobed (subisolobate). The two lobes of the upper-lip are (mostly only shallowly) notched at the distal margins (Fig. 1B–D, F–H), the three lobes of the lower-lip are longer and at its distal margins deeply notched (up to ¼ –1/3 of its length; Fig. 1G–H). The most striking feature that separates P. rosmarieae from other Andean Pinguicula taxa is the more or less uniform straight tube-spur-complex that appears as almost entire. The typical tri-partite divided Pinguicula corolla (i.e. into corolla lobes, tube and spur) appears nearly bi-partite here and is divided only into the corolla lobes and the tube-spur complex. The funnel-shaped, cylindrical tube merges ventrally into the short and comparatively wide cone-shaped spur, lacking a sharp angle (Fig. 1A, B). The spur is stubby, rounded at the apex and light yellow-green. The back of the tube only weakly protrudes from the spur: from this point, the stubby spur slightly attenuates proximally and ends in an obtuse apex. Looking at the corolla from a lateral (Fig. 1B) or semi-ventral (Fig. 1C) perspective, the tube and spur are not markedly separated. The tube-spur-complex is lengthwise dark parallel-veined. A tri-partite yellow to white palate is only weakly developed (Fig. 1H, i.e. non clapper-like as, for example, in P. calyptrata – Fig. 1I) and placed immediately behind the corolla lower-lip middle lobe (that appears as a shallow yellowish-greenish shimmering dent on the ventral tube-side directly behind the base of the middle lobe).

To illustrate the differences that can be observed on herbarium specimens, we have chosen Pinguicula calyptrata (Bussmann et al. 16447 MO, barcode: MO 6589755, Fig. 2C) collected in the immediate neighbourhood of the P. rosmarieae-type population (Fig. 2A). The sheet shows three well-preserved, single-scaped flowering specimens with the flowers in lateral profile view. The leaf rosette with its curled-up leaf margins measures up to ~30 mm in diameter. The flowering scapes are up to ~50 mm tall; the flowers are up to ~12 mm long (spur included), the corolla is distinctly tri-partite into the lip, tube and spur; its lobes are nearly equal-sized (subisolobate), the lower-lip middle lobe is only slightly larger than the lateral lobes, ~5 mm long; the corolla tube is distinctly funnel-shaped (at throat widest, ~5 mm), about as long as the corolla lobes, ~5 mm long; the spur is distinctly separated from the tube, short, ~2.5 mm long, thin, at apex rounded (sometimes almost imperceptibly thickened), angled at about 60°–90° with the length axis of the tube. Overall, in P. calyptrata as in the other Andean Pinguicula-taxa, the corolla is distinctly divided into three parts: lip, tube and angled spur.

Contrarily, in P. rosmarieae, the corolla appears bi-partite: tube and spur form a straight uniform funnel-cone-shaped tube-spur-complex, i.e. the spur is not angled with the tube. These features are clearly visible on the specimen collected by Paníagua-Zambrana, Bussmann & Vega Ocaña 8586 (MO 6607881; Fig. 2B), gathered in the surroundings of the Laguna Huay(ll)abamba (Department San Martín). The plants were found growing either as lithophytes on a vertical rock wall in the spray of a small waterfall or as epiphytes on twigs of Polylepis multijuga. They are distinguished by a spread-out 6–8 leaved rosette appressed to the ground. Its flower shows the striking straight uniform tube-spur-complex which we also observed in the Laguna de los Cóndores-Pinguicula (see the three specimens on the left-hand side of the sheet). Photographs (Fig. 1H, I) of the corollas (frontal view) support the deep morphological disparity between the two taxa.

In P. rosmarieae (Fig. 1H), the corolla is widely open and appears radially symmetrical at first sight. The corolla lobes are spread out, the two lobes of the upper lip are smaller than those of the lower-lip, their distal margins are shallowly notched (to ~1/6 of their length). The lower-lip lobes are much larger, deeply notched (to ~¼ –1/3 of their length). The throat and the adjacent tube portion are not dark, a pronounced palate is not developed; it is replaced by a weak yellowish shimmering patch at the base of the corolla lower-lip middle lobe, continuing proximally (to the middle of the tube-spur-complex) lengthwise in two white hairy stripes.

In P. calyptrata (Fig. 1I), the corolla is widely open and also appears radially symmetrical. The corolla lobes are spread out, covering each other slightly with their lateral margins. They are nearly equal in size, except for the middle-lobe of the lower-lip that dominates the corolla to a certain degree. The distal margins of all corolla lobes are only shallowly notched, the throat being dark-purple coloured. Nearly 2 mm behind (proximally) the middle lobe, at the base of the lower-lip, a pronounced yellow clapper-like palate is inserted, from which two white hairy stripes stretch out into the tube.

The Departments Amazonas and San Martín in northern Peru partly occupy the Sierra zone between the dry coastal region (Costa) and the upper Amazon river lowlands (Selva) and are largely characterised by extensive and very species-rich, cloud forests and wet subalpine grasslands (páramos). In contrast to Pinguicula calyptrata, which is largely found on wet, often peaty, soils, in the páramo region, Pinguicula rosmarieae occupies a completely different, even wetter, habitat. The species has been found either growing on steep, often vertical, rock-walls, normally on sandstones, in the spray of waterfalls (Fig. 3A, B) or rarely as an epiphyte in dense moss layers on Polylepis multijuga (Fig. 3C). Both represent equally extreme habitats, with extremely wet, nutrient-poor and acidic conditions and considerable mechanical stress.

The population at the type location grew in full sunlight on a steep sandstone cliff immediately above the famous tombs built by the Chachapoyas culture (AD ca. 800–1500). The tombs were built underneath natural overhangs, thereby allowing dry storage of the mummies. The type population (Henning & Schneider 275) grows above these overhangs exposed to constant dripping water and the general high precipitation typical for the eastern slopes of the Andes in this region (Fig. 3A).

Pinguicula rosmarieae is endemic to the northernmost foothills of the Cordillera Central in northern Peru. The herbarium specimens, known so far, are from three nearby collections in the same mountain range southeast of Leymebamba, stretching over some 15 km in a north-south direction. Both expedition teams have mistakenly located the collection sites in the adjacent western Departments (Amazonas and La Libertad, respectively), since the border runs along the pass of the Cordillera. According to current online map-sources (Google maps), all populations, deposited in herbaria so far, were found some 4–6 km east of the border to San Martín (Fig. 4). The presumed narrow endemism has just recently been rebutted by the report of the new taxon from the Province of Bongará in the Department Amazonas some 100 km further north. Photographs made by L. Santa Cruz Cervera clearly show the characteristic rosette and flower patterns of P. rosmarieae, photographed in a similar open habitat near the famous Gocta falls. However, the taxon seems restricted to the northern branches of the Cordillera Central, but reaches further into the northernmost foothills. The collection data indicate that P. calyptrata and P. rosmarieae show distributional overlap over the entire range of the latter. True sympatry is nevertheless prevented by the different habitat requirements of the two taxa.

The area lies well in the so-called Amotape-Huancabamba Zone, an important biodiversity-hotspot that spans from the Pacific coast over the cordilleras to the tropical lowlands of southern Ecuador and large parts of northern Peru (Fig. 4, for details see: Weigend 2002, 2004;). Many plant groups have a centre of diversity here (Weigend et al. 2005; Struwe et al. 2009; Deanna et al. 2018) and show a concentrated occurrence of narrow-endemic taxa in that region (Berry 1982; Ayers 1999; Weigend 2002; Henning and Weigend 2009, 2009a; Henning et al. 2019). While the vegetation and flora of the inner-Andean valleys and the western slopes are relatively well-investigated, the eastern flanks of the Cordillera Central facing Amazonia are still under-collected in many areas. Especially, the areas east of Leymebamba (Dept. Amazonas) in the north and Buldibuyo (Dept. La Libertad) in the south remain largely unexplored, since the eastern slopes can only be reached by foot. Single collection trips have yielded unexpected, supposedly narrowly endemic taxa in other plant groups, although only a tiny fraction of the area could be sampled to date (e.g. Loasaceae: Nasa rugosa subspp. gracilipes and pygmaea; Henning et al. 2011).

The whole region is characterised by great geological diversity, with large areas of dolomitic karst, caused by the exceptionally high rainfall (the indigenous Chachapoya were often called “warriors of the clouds”), interspersed with small areas of sandstone outcrops and metamorphic rocks. The vegetation of the sandstone areas is particularly intriguing, with many endemic species and unique vegetation types (e.g. Weinmannia sp. and Polylepis multijuga-Iochroma stenanthum dominated forests). P. rosmarieae has been found exclusively in the spray of waterfalls on sandstone cliffs and as an epiphyte on Polylepis – both systems characterised by extreme moisture and almost permanent cloud cover, a fact that is recognised in the local topographic maps, which often simply indicate “clouds” in these areas.

Pinguicula is yet another example of a plant group that is present in the Amotape-Huancabamba Zone with an endemic taxon, whereas its widespread relatives have their distribution limits at the zonal boundary, either seen from within (P. calyptrata) or outside (P. involuta). Since Pinguicula rosmarieae has been collected in those areas of the overall region that are comparatively easy to access, it cannot be ruled out that there are additional taxa awaiting discovery. However, the nondescript shape of the insectivorous butterwort, represented by only a few, widespread taxa outside of that region (Fig. 4), does not encourage gathering.

On a broader scale, the endemism of P. rosmarieae is by no means a unique phenomenon amongst the South American Pinguicula. P. jarmilae Halda & Malina from southeast Bolivia (Department Chuquisaca, municipio Villa Serrano, village Nuevo Mundo), for example, is only known from the type locality (Halda et al. 2007). Although it grows on vertical sandstone (laterite) rock faces under flowing/moving water, its morphology is quite different from that of P. rosmarieae: the superficial similarity is likely coincidental and does not reflect a close relationship between the two taxa.

Due to the aforementioned lack of a continuous botanical exploration of the region, we have to consider P. rosmarieae as Data Deficient (DD), according to the IUCN threatened species assessment guidelines (2001, 2017). However, within its distributional range, it seems to be limited to the easternmost ridge of the Cordillera Central. As an insectivorous plant, it seems to be adapted to special habitat types, characterised by ‘open’ vegetation, high precipitation and nitrogen-poor soils. These habitats might only be available in a narrow altitudinal band along the mountain chain. As our observations suggest, such sites are not present at similar altitudes in the west and it is very likely that suitable habitats are only available a few kilometres further east up to the lower altitudes of the Andes. This might indicate that P. rosmarieae is generally a rare taxon and might, thus, be vulnerable to habitat destruction. The lack of additional collections emphasises this assumption. This delicate butterwort might be in danger of extinction, but more data is needed to better assess the entire distribution and abundance, especially to the east of the known populations.

Peru. “Dept. Amazonas: Distr. Chachapoyas” (sic!) = Dept. San Martín, Prov. Huallaga, Lei[y]mebamba, Oseres [10 km east of Leymebamba]. Bosque Montano, 2542 m a.s.l. (~06°58'S, ~77°40'W), 22 May 2015. C. Vega Ocaña, L. Cotrina P., J. Valle, R. W. Bussmann, & N. Paniagua Zambrana 247 – HAO, MO 2852736. dp! [Det. Pinguicula RBU 2015; involuta E. Feltz (Ma), 2016]. – Duplicate: MO 6726506. “Dept. La Libertad, Distr. Uchumarca” (sic!) = Dept. San Martín, Prov. Huallaga, páramo and sandstone cliffs east of Laguna Huay(ll)abamba (06°58'53"S, 77°43'09"W) 3250 m a.s.l., 02 Nov 2012. – N. Paníagua Zambrana, R. W. Bussmann & C. Vega Ocaña 8586 [det. Pinguicula involuta RBU 2015]. – MO 6607881. dp!

Peru: Dept. Piura: [Prov.] Huancabamba, Lomas Redonda (Sapalache-Chinguelas) 2400 m (05°09'S, 79°26'W) a.s.l., 15 Ago 1981. A. Sagástegui Alva & al. 10187 – MO 2940293 [Barcode 348636], MO 4025844 [Barcode 348635] (dp!), HUT (dp!) – (det. P. involuta P. Taylor & M. Cheek). Dept. Lambayeque: [Prov.] Ferreñafe, [Distr.] Incahuasi cerca a la laguna Tembladera. Vegetación de jalca, zonas humedas. 3300 m a.s.l. (~06°09'S, ~79°19'W). 08 Oct 1989. S. Llatas Quiroz 2606 – F 2051195 (dp!). (det. P. involuta P. Taylor 1992). Dept. Cajamarca: Prov. San Ignacio, Distr. Tabaconas, Local. Santuario Nac. Tabaconas-Namballe, alrededores de las lagunas Coyona (Arrebiatadas), 05°14'S, 79°16'W (Arriba Laguna Lagartocha), 3140 m–3180 m a.s.l.. S. M. Baldéon Malpartida 5108 & L. Adriazon Ocupa. – USM 00266675 dp! (det. P. involuta). – Cajamarca, km 30 de la carretera Cajamarca-Bambamarca Jalca, estepa de gramineas, sobre un afloramiento rocoso. 3600 m a.s.l., 23 Mar 1985. – Sánchez-Vega, I. M., U. Molau & L. Ohmann 3756. – F 2216084 (Barcode V0469923F - dupl. CPUN; dp! det. Pinguicula L.) – [Prov.] Santa Cruz, [Distr.] Pulán, [caserio] El Molino, 2,500 m a.s.l. (06°46'S, 78°55'W), 12 Feb 2007. L. Santa Cruz, M. Chocce & M. Beltrán 996– USM 241552 (dp!), HUT 50771 (dp!). – [Prov.] Santa Cruz, [Distr.] Pulán, Pampa el suro, 2500 m a.s.l. (06°50'S, ~78°54'W), 31 Ene 2008. L. Santa Cruz 2098 – HAO, USM 240752 (dp!). – Prov. San Miguel, distrito Tongod, Bosque San Pedro Norte (06°45'S, 78°49'W), 03 Nov 2001. I. M. Sánchez Vega & M. Sánchez M. 11122 – F 2245015 [V 0410057F] (dp! det. P. involuta). Dept. Amazonas: [Prov.] Bagua, [Santuario Nacional] Cordillera [de] Colan-La Peca, 9600 ft a.s.l. (05°35'S, 78°14'W), 29 Aug 1978. Ph. J. Barbour 3222 – USM 53585 (pd!), MO 2798203 (dp! – Barcode MO 348631, det. P. involuta P. Taylor 1992). – Cordillera Colan-La Peca, 9600–11075 ft a.s.l. (05°35'S, 78°16'W), 08 Sep 1978. Ph. J. Barbour 3425 – F 1909251 (V0469936F; dp!), MO 2789874 (pd! det. P. involuta Taylor). – Amazonas: 3000–4000 m a.s.l. (~06°07'S, ~77°39'W), 09 Nov 2012. H. van der Werff, L. Valenzuela, G. Shareva & A. Reyes Barrantes 25401 – MO. – Cerro de Fraijaca (Huaui-Huni) n. e. Tambo de Ventilla. Jul 07 1948. A. W. Pennell 15875 USM 90946 (det. Pinguicula - dp!). – Prov. Chachapoyas, declives superiors de [Cerro] Puma-Urcú, [~2 km] este-sureste de [ciudad] Chachapoyas (~06°14'S, ~77°52'W), alt. 2700 m. – 3000 m., Jun 01 1962. J. J. Wurdack 679. – USM 90948 (dp!), COL (dupl. dp! det. P. antarctica, by Fernandes-Pérez 1964), NY. – Prov. Chachapoyas, bosque bajo y húmedo al lado de (moist scrub forest on south side of) Molinopampa-Diosan pass, alt. 2700 m – Balsa road to Leymebamba, just below Abra Callacalla (= Alba Barro Negro) on the slope towards Leymebamba, 3559 m a.s.l. (06°44'S, 77°53'W), 19.10.2000 – M. Weigend, E. Rodríguez R., H. Förther & N. Dostert 867 – USM 166766 (dp! det. Pinguicula spec.) – [Prov.] Chachapoyas, [Distr.] Balsas, En el Paso de Calla Calla (06°48'S, 77°53'W), 07 Oct 2001. I. M. Sãnchez-Vega, M. Sãnchez, M. 11061 – F. – Cerros [Cordillera] Calla Calla. 26 km above Leimebamba, road to Balsas. Km 403, 3360 m a.s.l. (~06°48'S, ~77°53'W), 16 Oct 1964. P. C. Hutchison & J. K. Wright 6993. – MO 2233627 (GBIF: as P. antarctica); USM 90947 (dp!). – Prov. Chachapoyas, Distr. Chachapoyas. Trail to Laguna de Los Cóndores, surroundings of Laguna Esperanza/Siete Lagunas (06°49'S, 77°43'W) 3275 m–3500 m a.s.l., Jun 26 2010. R. W. Bussmann, A. Glenn, G. Chait & C. Vega Ocaña 16447. Dept. La Libertad: Distr. Uchumarca, páramo in the surroundings of Vira Vira/Lagunas La Quinuas (07°00'S, 77°45'W), 3050 m a.s.l. – Photograph: R. W. Bussmann (det P. involuta = P. calyptrata).