Viola imbricata K.Menegoz & J.L.Celis-Diez, 2024

Menegoz, Kora, Watson, John M., Flores, Ana R., Cofré-Valenzuela, Pedro E., Ortúzar-Simonetti, Marcelo A. & Celis-Diez, Juan L., 2024, Viola imbricata (Violaceae) a newly discovered local endemic of subgenus Neoandinium from the Andes of Maule and Ñuble Regions, central Chile, Phytotaxa 677 (3), pp. 218-232 : 221-227

Viola imbricata K.Menegoz & J.L.Celis-Diez , sp. nov. ( Fig. 2–4 )

Type :— CHILE. Ñuble Region , Punilla Province , San Fabián de Alico, Cerro la Pila, 36°39’30.58” S 71°13’9.79” W, 2345–2650 m elevation, 22 December 2020, K. Menegoz & A. Castillo 122 (holotype SGO 171249 !; isotype CONC 191491 !) .

Diagnosis:—The new species differs from all other taxa of the Sempervivum section of Viola subg. Neoandinium by the combination of its proportionately large bulbous calyx and diminutive yellow corolla of less than 8 mm diameter with bearded lateral petals. Its nearest relative, Viola abbreviata J.M. Watson & A. R. Flores (2019b: 36) has similarly densely imbricate dome-shaped to columnar rosettes, and small corollas, but these are white and glabrous. The latter also has a disjunct distribution in adjacent Argentina on the eastern exposure of the Andes. The newly described species also resembles Viola auricolor Skottsb. (1916: 260) in view of its flowers colours, but differs by having smaller flowers (6.2–8 mm vs. 10–15 mm wide), a clearly different shape of rosette (dome-shaped to columnar rosette with more than 10 spirals of densely imbricated leaves vs. simple rosette with rarely more than 10 spirals of loosely imbricated leaves), and its northern distribution (Maule and Ñuble Regions in Chile vs. Río Negro, Chubut and Santa Cruz Provinces of Argentina and adjacent Chilean Aysén Region).

Description:— Life form perennial , subacaulous, rosulate, glabrous, evergreen hemicryptophyte. Rootstock axial, 13– 35 cm long × 3.4–4.5 mm dia. at junction with caudex, subligneous, solitary above, branching into several multiple feeder roots near subterranean apex. Caudex 8–20 × 1 cm, simple, cylindrical, enveloped densely in remains of dead vegetation. Plant usually solitary, occasionally forming groups of up to 9 rosettes. Rosette 3–7 cm dia. × 2.7–8 cm high, densely imbricate to base, columnar to dome-shaped basally below face, this of lesser diameter, flattened and depressed, strongly so towards centre; face of rosette green, green to pale brown basally. Leaves pseudopetiolate, spathulate, estipulate, ca. 1–2.7 cm when mature, arranged in distinct spirals on rosette face; pseudopetiole 15.5–19.5 × 1.5–1.7 mm, narrowly plane; lamina 5–5.7 × 5.7–7 mm when mature, entire, broadly obovate, ovate, suborbicular or rhomboid, subcuneate to pseudopetiole, carnose-succulent and rigid when mature; margin pale-translucent, narrow, thin-cartilaginous, irregularly serrulate on the first half lower part of the leaf blade, entire on the upper part; face green basally, reddish or brownish apically with narrow dark red line round apical margin; apex apiculate. Anthesis more or less synchronous, but prolonged-successive. Flowers 5–7 mm high × 6.2–8 mm wide, axial, solitary, forming dense multiple outwards-facing ring of 20 or more open corollas around upper circumference of rosette face. Peduncle 13–13.5 × 1.2 mm, shorter than submature leaves; bracteoles situated shortly above base, 5–5.3 mm, opposite, free, narrowly linear with acuminate apex, hyaline. Calyx 3–3.3 mm dia, bulbous, entire basally, free above, green, red spotted at base; sepals 12–13.5 × 1.2 mm, equal, entire, lanceolate acute where free from subbasal area, acuminate, margin translucent-cartilaginous. Corolla yellow overall, with dense discontinuous radiating venation on inferior petal, this occasionally also sparsely present on basal half of lateral petals; petals deeply inserted into calyx to ca. half length; superior petals 3.5–4.5 × 1.6–2 mm, obovate, cuneate to base, reflexed; lateral petals 4.5–5.5 × 2.5 mm, suborbicular, cuneate to base, long white-pilose basally, light brown discontinuous narrow veining occasionally present on basal half; inferior petal (including horizontal base at spur mouth) 6–6.8 × 3–3.4 mm, obtriangular, dense dark brown narrow, radiating subdiscontinuous branching venation extending to apex, thickly white short-bearded at mouth of spur; apex truncate, slightly emarginate, miniscule mucro in sinus; spur 1–1.8 mm × 0.9–2 mm maximum diameter, cylindrical-bulbous, shortly protruberant directly behind conjoined inferior petal, apex rounded. Androecium and gynoecium exserted, readily visible; anthers 5, free, 2–2.5 mm, inferior pair with 2 tapering 2 mm nectar glands; connectives shorter than anthers, dull orange; style 2.7–3 mm, subgeniculate, clavate; ovary superior, single-celled, triplacental, 1 × 1.5 mm; stigma small circular frontal aperture sited between style crest lobes; style crest ca. 0.8 × 1 mm; trilobed, lateral lobes either side of style head, entire, broad, long-acuminate, upcurved; central lobe apical, triangularacuminate, entire, short, somewhat recurved. Fruit trivalved dehiscing capsule, 9 × 7 mm. Seeds not seen.

Etymology:—The epithet imbricata refers to the densely imbricated leaves of the plant rosette, which form beautiful mandalas in the high mountain ranges.

Distribution and habitat:—Endemic to the highest Andean ranges of the southern Province of Maule Region and northern Province of Ñuble Region, Chile ( Fig. 1 ). Specifically, 5 sites are known, two of them located in San Fabián de Alico, Punilla Province, Ñuble Region: (1) Cerro la Pila, 2345–2650 m elevation, 36°39’30.58” S 71°13’9.79” W; (2) Cerro Blanco, 2579 m elevation, 36°38’29” S 71°13’4” W; the others located in the Achibueno watershed, Linares Province, Maule Region (1) North slope of the Nevado de Longavi volcano, 2600–2800 m elevation, 36°11’14” S 71°09’42” W (2) Cordón de la Quemada, 2475–2590 m elevation, 36°2’40” S 71°9’24” W, and (3) Cerro el Toro, 2375–2870 m elevation, 36°0’31.15” S 71° 7’54.58” W. The maximum distance between the sites is 72 km. Viola imbricata usually grows at high elevations (2300–2900 m), to the upper elevational limit of vascular plants. Due to snow melting, these sites’ soils remain relatively humid during the dry season. The species always grows on rocky sites but its habitat exposure and slope gradient are variable.

V. imbricata is one of the plants with the highest elevation record in the regions where it grows, close to glaciers in some cases (Nevado de Longaví and Cerro el Toro), in rocky environments, between small and medium-sized rocks ( Fig. 2 ). Although snowfall is declining due to climate change, these areas still remain covered by snow during all winter and spring months.

Associated vegetation:—From the phytogeographic point of view and according to the classification of Luebert & Pliscoff (2017), Viola imbricata is part of two vegetal formations – high elevation low shrubland and high elevation grassland – and several vegetative belts: (1) Andean temperate low shrubland of Discaria chacaye (G. Don 1932: 35) Tortosa (1983: 80) ( Rhamnaceae ) and Berberis empetrifolia Lamarck (1792: 391) ( Berberidaceae ) in San Fabián; (2) Andean mediterranean low shrubland of Laretia acaulis ( Cavanilles 1799: 59) Gillies & Hooker (1830: 329) ( Apiaceae ) and Berberis empetrifolia, Andean mediterranean grassland of Oxalis adenophylla Gillies ex Hooker & Arnott (1833: 165) ( Oxalidaceae ) and Pozoa coriacea Lagasca (1816: 13) ( Apiaceae ) in Nevado de Longavi volcano; (3) Andean mediterranean low shrubland of Laretia acaulis and Berberis empetrifolia in Cordón de la Quemada and Cerro el Toro.

Our field observations in San Fabián indicate a total of 8 species associated with Viola imbricata : one Cerastium sp. Linnaeus (1753b: 28) ( Caryophyllaceae ), Combera paradoxa Sandwith (1936: 3325) ( Solanaceae ), Gamocarpha scapigera (Rémy in Gay 1848: 250) Denham & Pozner (2019: 225) ( Calyceraceae ), Nassauvia lagascae (D. Don 1832: 389) Meigen (1894: 441) var. lanata ( Philippi 1894: 87) Skottsberg (1916: 329) ( Asteraceae ), Olsynium junceum (Mey. ex Presl 1827: 118) Goldblatt (1990: 508) (Iridiaceae), Oxalis compacta Gillies ex Hooker & Arnott (1833: 162) ( Oxalidaceae ), Pinnasa nana (Philippi 1893: 14) Weigend & Acuña (2017: 373) ( Loasaceae ), and Pozoa coriaceae .

In Nevado de Longavi, 9associated plants were observed: Bromus sp. Linnaeus(1753b:76) ( Poaceae ), Chaetanthera villosa D. Don (1932: 391) ( Asteraceae ), Epilobium glaucum Philippi (1864: 70) ( Onagraceae ), Gamocarpha alpina (Poepp. ex Lessing 1931: 258) H.V. Hansen (1992: 65) subsp. alpina ( Calyceraceae ), Gamocarpha scapigera , Grausa lateritia (Gillies ex Arnott 1931: 275)Weigend & R.H.Acuña in Acuña et al. (2017:374)( Loasaceae ), Nassauvia digitata Weddell (1855: 48) ( Asteraceae ), Nassauvia revoluta D. Don (1932: 390) ( Asteraceae ), and Poa sp. Linnaeus (1753b: 67) ( Poaceae ).

Phenology:—Flowering from December to January, just after snow melting. Seed dispersal about one month later for each flower.

Considered conservation status:— Viola imbricata is assessed here as Critically Endangered ( CR) under the IUCN categories and criteria B 2ab(iii). Criterion B 2 was selected because its area of occupancy is <10 km 2 (0.62 km 2). Criterion “a” was selected because the population is severely fragmented, restricted to the top of the highest mountains of two localities separated by a distance of 50 km. Criterion “b(iii)” was selected because there is a projected decline in the area, extent, and quality of habitat. These high mountain sites are remote from any occupied territory as the new species inhabits fairly inaccessible rugged terrain. However, both subpopulations are in areas where tourism is developing fast, with scarce territorial planning and regulations. Also, many mining explorations have been carried out close to the sites of San Fabián, and this subpopulation could be affected by local climate change effects caused by water reservoirs ( Li et al. 2023) due to the projected construction of a large hydroelectric dam in the Ñuble valley. In addition, the effects of increased temperatures and the consequent reduction in prolonged snow cover due to global climate change represent a severe threat of potential extinction to this environment-sensitive taxon. Climate change has promoted the upward shift in the elevational limit of the vegetation in alpine ecosystems ( Lenoir et al. 2008; Tovar et al. 2022). Since the species occurs near the summits of mountain ranges, with a limited capacity to migrate to higher elevations, we project a continuing decline in the area and quality of habitat in the coming decades. Less than 200 individuals were recorded from the type site, and our estimations for the other sites are similar. Finally, Viola imbricata is not present in any protected area in Chile.

Additional specimens examined (paratypes):— CHILE. Maule Region, Linares Province, Nevado de Longaví, N exposure, 36°11’14” S 71°09’42” W, 2722 m elevation, 19 January 2022, J. L. Celis-Diez ( CONC 194769!).

Key to distinguish Viola imbricata among yellow to orange flowers species of Sempervivum section found in South America from Central Argentina and Chile to Patagonia, based on Nicola (2017), Watson et al. (2022) and Marcussen et al. (2022).

1. Corolla facing upwards within the circumference of the rosette.......................................................................................................2.

- Corolla facing outwards within the circumference of the rosette......................................................................................................3.

2. Sepals ca. 8 mm long; spur ca. 10 mm long; anthers unciliated; style crest infundibuliform North Patagonia, Argentina (Neuquén Province).......................................................................................................................................................................... V. coronifera

- Sepals ca. 5 mm long; spur ca. 4 mm long; anthers densely ciliated; style crest subtrilobed. North Patagonia, Argentina (Neuquén Province).............................................................................................................................................................................. V. comberi

3. Simple rosette with rarely more than 10 spirals of loosely imbricated leaves; corolla large, 10–15 mm wide, clearly twice or more as wide as mature leaf blade. Central Patagonia , Argentina (Río Negro, Chubut and Santa Cruz Provinces) and adjacent Chile (Aysen Region) ................................................................................................................................................................. V. auricolor

- Dome-shaped to columnar rosette with more than 10 spirals of densely imbricated leaves; corolla small, less than 8 mm wide, less than twice as wide as mature leaf blade. Central Chile (Maule and Ñuble Regions) ................................................. Viola imbricata

Figures

FIGURE 1. Distribution maps of Viola imbricata (A, B, C). A: Chile. B: Subpopulations of Maule (α) and Ñuble (β) Regions. C: Sites of V. imbricata (red stars), contour lines every 150 m elevation.

FIGURE 2. Detail of different growth habits and substrate recorded in colonies of Viola imbricata. A, B: Rocky habitat of Viola imbricata. A, C: Groups of rosettes. D, E, F: Rosette evolution from dome-shaped to columnar habit. Photographed by Fabián González (C), and Alvaro Castillo (A, B, D, E and F).

FIGURE 3. Viola imbricata. A, D: Flowers. B: Anthers, inferior pair with nectar glands. C: Gynoecium. E: Sepals and leaf upper side. F: Leaf underside with venation. G: Imbricated leaves. H: Caudex. I: Rootstock. J: Fruits. Photographed by Cesar Muñoz (A, I, and J), Alvaro Castillo (D and E), and Kora Menegoz (B, C, F, G and H).

FIGURE 4. Viola imbricata. A: Flowered plant with caudex and rootstock, lateral view. B: Rosette with capsules, upper view. C: Flower with peduncle and bracteoles, lateral view. D: Gynoecium showing style crest from lateral view. E. Gynoecium showing style crest from frontal view. F: Flower, frontal view. G: Mature leaf, upper side. H: Mature leaf, underside. Drawn by Lorena Sánchez.