Corryocactus volcanicus A.Pauca & Hoxey, sp. nov.

Type: — PERU. Department Arequipa, Province Castilla, District Andagua: Above Andagua. Flat ground, not rocky, used for grazing, 15°29′30.0768″S, 072°22′24.7008″W), 3740 m, 01 March 2024. Hoxey & Pauca 237 (holotype HSP!).

Diagnosis:— Corryocactus volcanicus is similar to C. brevistylus from which it differs by the colour of the tepals, filaments and anthers of the flower (whitish vs. golden yellow), flower length (70–77 mm vs. 80–110 mm) and flower diameter at anthesis (50–53 mm vs. 70–100 mm), absence of a constriction between pericarp and tube (vs. present), the rigidity of the spines on the fruit (flexible and soft vs. rigid), and in the length of the seeds (1.76–1.90 mm vs. 2.08–2.25 mm).

Description (Fig. 1A): — Large shrub to columnar plants, up to 3 m tall, with basal branching. Stems erect, epidermis light green, 100–120 mm in diameter. Ribs 7–10, 22–28 mm high. Areoles circular, 9–19 mm in diameter and separated by 21–30 mm, with greyish felt in older areoles but black felt with a small brown tuft towards the rib in new ones. Young areoles with small deltoid scales of a green-yellowish colour. Spines (12–)14–17 (but as high as 50 in basal areoles on the trunk), smooth-surfaced, usually straight, sometimes slightly curved. Radial and central spines indistinguishable, 6–105 mm long, gray when old, yellow when new, yellowish base with a brownish tip when developing. Flowers (Fig. 1C & 2) usually sub-apical, diurnal, actinomorphic, funnel-shaped, 50–53 mm in diameter and 72–77 mm long at anthesis. Pericarpel greenish, 21–27 mm in diameter and 16–24 mm long, with dark green deltoid scales, 0.7–2.9 mm long. Rounded areoles 1.6–2.4 mm in diameter, with brownish-black felt and some whitish curly hairs. Spines 3, 3–4 mm long, straight, yellowish. Hypanthium tube with scales, hairs, and areoles similar to those of the pericarpel. Ovary whitish, 9–10 mm wide; Style whitish, cylindrical, glabrous, short and thick, 13–14 mm long and 4–5 mm in diameter. Stigma lobes yellowish, 20–24, 10–13 mm long, papillose surface. Nectar Chamber located at the base of the style. Stamens numerous from near the base of the style, filaments glabrous, pale yellow, 9–14 mm long, anthers yellowish, basifixed, lateral dehiscence, 2 mm long. Outer tepals glabrous, greenish with brownish, acute apex, apiculate. Inner tepals glabrous, spatulate, notched, apiculate, pale yellow, almost white, the apex a pale pink, 16–33 mm long and 3–10 mm wide. Fruit (Fig. 1B) globular, 75 mm in diameter, greenish-yellow pericarp. Pulp translucent and sour-tasting. Areoles with blackish felt, with numerous spines 27–33, up to 20 mm long, thin, flexible and yellowish. Seeds, brownish-black, broadly oval, asymmetrical, medium-sized, 1.76–1.90(–1.95) mm long, (1.20–)1.26–1.33(–1.35) mm high, 0.65–0.79(–0.98) mm wide, with a mucilage sheath, dull, rough, testa edge expanded towards the hilum, cells gradually smaller towards the hilum, isodiametric cells, channelled anticlinal boundaries, micropyle and hilum together in one region but separated by a band of sclerenchymatic tissue, length of the hilum-micropylar region (0.50–)0.60–0.70(–0.79) mm.

Etymology: —This species is named due to its restricted distribution in the Valle de los Volcanes (English: Valley of the Volcanoes) in Andagua, Castilla, Arequipa. The area is characterized by the presence of numerous extinct monogenetic volcanoes, with the landscape and soils shaped by their eruptions. Currently, the is part of the Colca y Volcanes de Andagua Global Geopark (GMU-CVA), recognized by UNESCO.

Distribution and habitat: — Corryocactus volcanicus is restricted to the Valle de los Volcanes (Department Arequipa, Province Castilla, District Andagua), within the drainage basin of the Río Andagua, in the localities of Andagua, Chachas, Sucna, Chipchane, Nahuira, and on the road to Ayo, with an elevation range of 2700–3800 m a.l.m. (Fig. 3). The distribution area is estimated to be approximately 112 km ². Within the distribution area, individuals show little variation in morphological characters, and no typical specimens of C. brevistylus have been observed (the latter is also commonly found in xerophytic shrub ecosystems), likely indicating a geographic isolation. C. volcanicus grows on the slopes of hills or on somewhat flat terrain, in rocky or sandy soils, often associated with volcanic scoria rocks. In some areas, the density of individuals is high, forming stands or “cactus forests”. Flowering and fruiting occur at different times of year, with the former appearing from August to November and the latter developing from December, with ripe fruits found by the end of January. This endemic species is associated with typical species of the pre-Andean xerophytic scrub (Chicalla-Rios 2021, Montesinos-Tubeé et al. 2012).

Conservation status: —The threats to Corryocactus volcanicus include extractive activities related to artisanal mining and anthropogenic forest fires, both of which have been observed in the area. Additionally, climate change, with increasingly recurrent extreme rainfall and drought events, is also noted.

According to the IUCN criteria, complemented by Bachman et al. (2011), the category Endangered can be assessd (EN, criteria B1ab(i,iii,iv); B2ab(ii,iii,iv)). The following considerations were taken into account: Area of Occupancy (AOO), Extent of Occurrence (EOO), population fragmentation (≤5) (a), reduction in the extent of presence (i) and in the area of occupancy (ii), a decline in habitat quality (iii), and a reduction in the number of locations or subpopulations (iv).

Discussion: — Corryocactus volcanicus shows morphological affinities with C. brevistylus and C. brachypetalus (Fig. 4; Table 1). The new species differs from C. brevistylus mainly in its pale yellow (almost white) flowers, smaller floral dimensions, flexible spines on the fruits (rigid in C. brevistylus), and smaller seeds with a shorter micropilar region. Although the two taxa occur within 24 km of each other, but C. volcanicus is geographically isolated by mountain ranges exceeding 5000 m in elevation.

Compared to Corrycactus brachypetalus (Fig. 4; Table 1), C. volcanicus can be distinguished by its pale-yellow flowers (yellow-orange to reddish in C. brachypetalus), soft and flexible fruit spines, and brownish-black seeds (black in C. brachypetalus). Ecologically, C. brachypetalus inhabits coastal lomas ecosystems, whereas C. volcanicus grows in pre-Andean shrublands at higher elevations, being separated by ca. 120 km and 2300 m in altitude.

The distribution of Corryocactus volcanicus is restricted to a small area of the pre-Andean xerophytic scrub in Arequipa, a vegetation type where C. brevistylus is widespread elsewhere. Probably, an ancestral population of Corryocactus was distributed in the Andean and coastal areas, which diversified during the Pliocene (Hernández-Hernández, et al. 2014), resulting in the current species (C. brevistylus, C. brachypetalus, and C. volcanicus) due to environmental changes and geographic isolation. It is possible that the geographic conditions of the Andagua Valley caused allopatric speciation by isolation of the ancestral Corryocactus population no more than 2–3 million years ago (Hernández-Hernández, et al. 2014; Luebert & Weigend, 2014). The Andagua Valley presents particular geographic characteristics, being enclosed by volcanic mountain ranges on three sides with rugged, and steep slopes. These mountains exceed an elevation of 5000 m in many places. The lowest part of the valley converges with the Río Colca, at about 1600 m of elevation. At these low elevations conditions are very arid. The high elevation mountains and the low elevation arid zone form a natural barrier enclosing the entire distribution C. volcanicus indicating a level of isolation (red polygon in figure 3). Furthermore, volcanic activity in the area is evident, influencing the current landscape and soil characteristics. The Valle de los Volcanes is still an under-explored region, and likely to contain other taxonomic novelties, as evidenced by the recently described new species Echeveria vulcanicola (Pino et al. 2019: 113).