Echeveria coruana morphologically resembles most E. patriotica and E. purhepecha, with which it shares a similar flower morphology, but differs from both in having acaulescent or inconspicuous stems, acuminate leaves, and corolla appendages at the base of antipetalous stamen filaments. It differs from E. patriotica in having smaller leaf rosettes, 10–15 cm in diameter, smaller inflorescences, 28–65 cm long, longer pedicels, (1.3) 1.6–2.2 mm and a narrower corolla, 7–9 mm in diameter. It can be distinguished from E. purhepecha by the larger rosettes with spreading linear-oblanceolate to spathulate leaves, 8–16 cm long, and the larger corolla, 15–20 mm long, light-yellow to orange in the median part and orange-reddish at the tips of corolla lobes.

MÉXICO. Michoacán: Municipio de Ziracuaretiro, lado noroeste de San Andrés Corú; 19°28.116'N, 101°57.410'W; 1730 m; bosque de encino-pino alterado con huertas de aguacate; 27 Nov 2015; I. García & M. García 9138 (holotype: CIMI!, isotypes: DAO!, ENCB!, IEB!, MEXU!, MICH!, WLU!).

Perennial herb, glabrous, acaulescent or with an inconspicuous caudex, 3–8 cm long and 1–1.3 cm in diameter; rosette lax, 10–15 cm in diameter with 15–18 leaves; leaves fleshy, light-green to dark green in the median part and apex, leaf blade linear oblanceolate to spathulate, 8–16 × 2–2.5 cm, 0.5–1 cm thick at the base, margin entire, occasionally with a thin, red-colored line, apex acuminate, short mucronate, base narrowed to form a pseudo-petiole, 2–3 cm long, corrugated ventrally; inflorescence paniculiform thyrse, 1–3 per rosette, 28–65 cm long and 0.3–0.5 cm wide at the base, with 1–4 secondary axes (cincinni), each with 1–4(5) flowers; bracts spiralled, adpressed, green to yellowish-red, oblanceolate to oblong-lanceolate, 0.8–7.2 × 0.6–3 cm, 1.2–1.5 mm thick in the median part and 7–8.5 mm at the base, base auriculate, soon caducous; pedicels (1.3–) 1.6–2.2 mm long and 2–3 mm thick; calyx gamosepalous, star-shaped, the tube 1–1.5 mm long, lobes green, unequal, 6–9 × 3–4 mm, spreading to somewhat reflexed at anthesis, triangular-lanceolate; corolla pentagonal-conical in bud, cylindrical-urceolate at anthesis, petals 15–21 × 4–6.5 mm, fused for 1–1.5 mm at the base, lanceolate, carenate, tips mucronate, erect to slightly deflexed, color whitish-yellow at the base, light-yellow to orange in the median part and orange-reddish at the tips; nectaries reniform, 1.8–2.2 × 0.8–1 mm, white-yellowish; stamens 10, 5 antipetalous, 9–16 mm long (including the anthers), with a pair of conical or dome-like appendages at the base, 0.2–0.3 mm long; episepalous stamens 5, 10–16 mm long (including anthers); pollen polymorphic, most abundant type is 3-colpate, oblate to oblate-spheroidal in equatorial view and triangular or round in polar view, 30–34 × 17–20 mm, less common grains are 3-colpate, prolate, 34–38 × 18–20 mm or 4-colpate, rectangular or spherical, 28–31 × 17–20 mm; in all pollen grains tectum is imperforate, scabrate; pollen grains eventually agglutinate into large masses; ovary with 5 apocarpous carpels, 9–11 × 0.3–0.4 mm; styles (including the stigmas) 4–5 mm long, red-purplish; follicles 5–6 mm long, erect to somewhat spreading; seeds numerous, oblong to obovate, light to dark-brown, reticulate, 0.5–0.65 × 0.2–0.25 mm; reticulum size 15–30 mm.

Figure 1. 

Habitat and general morphology of Echeveria coruana. A Habitat B Leaf rosette of type specimen C Developing plant (in cultivation) D–F Inflorescence D General view E Developing cincinus F Terminal cincinni G–H Flowers of type specimen viewed in the field from different angles I–J Flowers from type specimen fixed in FAAI Dissected flower (removed corolla) to show stamen bases and nectaries. J Conical appendages at the base of antipetalous staminal filaments (indicated with black arrows). Scale bars 1 mm.

Figure 2. 

Scanning electron microscopy of E. coruana, pollen and seed (García & García 9138). A–C Heteromorphic pollen grains; arrows indicate a few 3-colpate, prolate pollen grains B 4-colpate (left, upper) and 3-colpate pollen (right, down) grains C 3-colpate, prolate pollen grain D–E Seed morphology.

A detailed comparison of E. coruana with E. patriotica and E. purhepecha is presented in Table 1. If these three species are related from an evolutionary point of view, the corolla appendages have evolved at least two times in ser. Gibbiflorae. The antipetalous stamen appendages of E. coruana are considerably smaller and less complex than those of E. novogaliciana, E. marianae, E. dactylifera and E. rulfiana, the other species of ser. Gibbiflorae that are known to possess them (García and Costea 2014, Jimeno-Sevilla et al. 2015). García and Costea (2014) indicated that these appendages do not have a secretory function and their role may be to protect the nectar accumulated at the base of petals from pollinators lacking a specialized feeding apparatus. In E. coruana, the appendages are too small to cover the corolla cavities in which nectar accumulates. Alternatively, if E. coruana is evolutionarily related to these latter four species, the reduction of antipetalous corolla appendages in E. coruana likely indicates the loss of this hypothetical nectar defense function. Corolla appendages at the base of stamens have also evolved in Pachyphytum (Walther 1972, Thiede and Eggli 2007), a genus that forms a sister clade to the remaining “Echeveria group” (Carrillo-Reyes et al. 2009). A molecular study for ser. Gibbiflorae with more extensive sampling that of Carrillo and et al. (2009) is necessary to understand the evolutionary relationships among the numerous members of this group (Walther 1972), including the several recently described species.

The new species grows in the understory of mixed pine-oak and tropical deciduous forest on volcanic basaltic rocky outcrops or small ledges. However, it has also been observed growing epiphytically on Quercus sp. The tree layer is dominated by Quercus magnoliifolia Née, Ficus membranacea C. Wright, Juglans major (Torr.) Heller, Photinia microcarpa Standl., Bursera ariensis (H.B.K.) Mc. Vaugh & Rzed., and Clusia salvinii Donn.; the most common shrubs are Bursera bipinnata (Sessé & Moc. ex DC.) Engl., Montanoa bipinnatifida (Kunth) C. Koch, Montanoa frutescens (Mairet) ex DC. and Rhus terebinthifolia Schltdl. & Cham. The herbaceous understory vegetation includes among others: Arenaria lanuginosa (Michx.) Rohrb, Bonplandia geminiflora Cav., Tripogandra amplexicaulis (Klotzsch ex C.B. Clarke) Woodson, Phaseolus acutifolius var. latifolius G.F. Freeman, and Dryopteris maxonii Underw. & C. Chr.

November to January.

The specific epithet derives from San Andrés Corú, the nearest village to the malpaís where the species was discovered. “Corú” in the local Purhépecha language means “a place where the quails sing”.

Echeveria coruana is currently known only from three populations located at ca. 1–2 km from one another in the malpaís of San Andrés Corú. Although it is relatively common in the studied sites, it is threatened because of the increasing demand and exploitation of volcanic rocks in the area. Furthermore, the recent establishment of avocado orchards at elevations of 1670–1750 m has led to significant habitat loss in the area, and this practice is likely to continue in the future. Although it was not possible to use GeoCAT (Bachman et al. 2011) to calculate the extent of occurrence because of the reduced number of localities from which the species is known, we determined the area of occupancy, which was 8 square km (based on 2 km cells). Therefore, using the IUCN (2012) criteria B2 biii, we preliminarily categorize this species as Critically Endangered (CR). More research in the field will be carried out in the future to determine the best strategy to mitigate the above mentioned threats.

México. Michoacán: Municipio de Ziracuaretiro, Malpaís de San Andrés Corú, bosque de encino-pino, 1676 m, 1 Dec 2012, D. Valentín 502 (CIMI!, EBUM!); Malpaís de San Andrés Corú, lado oeste-suroeste de San Andrés Corú, 1660 m, 29 Apr 2015, I. García, D. Valentín and A. Fuentes 9078 (CIMI!).