kingdom Plantae - plants »  divisio Magnoliophyta - flowering plants »  class Rosopsida - eudicots » order Malpighiales »  family Violaceae »  tribus Violeae > genus Viola > Viola sect. Melanium  Ging. 

Viola guaxarensis M. Marrero, Docoito Díaz & Martín Esquivel

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Description: Description — Perennial cushion-forming herb with a clear overwintering period, to 20 cm tall × 50 cm in diam. Indumentum present on almost all structures of plant, comprising smooth, hyaline trichomes 0.1–0.2 mm long. Stems 4–5 cm long, subterranean, with green, fistulous, subtetragonous branches. Leaves 3-grouped, greenish, petiolate or subpetiolate, stipulate. Lower leaves (25–)30–45 × (8–)10–15 mm, ovate to orbicular-ovate, petiolate, generally subdentate, stipulate; stipules linear, entire and 2–3 × c. 2 mm or bisected with median lobe 3–5 × c. 1 mm. Upper leaves frequently unevenly dentate-crenate with short incisions, lanceolate to linear-lanceolate, (30–)35–45 × 5–7 mm, base cuneate, apex subacute, usually purple; petiole <5 mm long, shorter than lamina; central leaf normally without stipules; lateral leaves stipulate; external stipules 2- or 3-sect (main lobe 10–15 × 1–1.5 mm); internal stipules linear, 12–17 × 1–1.5 mm. Flowers axillary, solitary. Peduncle more than 2× length of leaves, 7–10 cm long, hairy, arcuate, subtrigonous; bracteoles purple, 3–6 mm long, subopposite, inserted in upper ½ of peduncle, usually slightly hastate. Sepals subequal, 10–13 × 3–4 mm at base, linear-triangular, acuminate, purple at base and margin; basal appendix 1.5–2 mm long, crenate-sinuate at base, usually with 2 or 3 incipient lobes. Corolla 25–30 mm in diam., white-cream to violet, occasionally entirely white, petals slightly eroded. Upper petals 13–10 × 8–11 mm, glabrous, obovate, apex subacute. Lateral petals 12–10 × 7–9 mm, oval, glabrous, slightly clawed and densely hairy at base of claw, apex rounded. Lower petals 11–14 × 9–11 mm, lightly coloured, yellow near spur, retuse, slightly conduplicate, glabrous. Spur 8–9 × 2–2.5 mm, arcuate, glabrous, purple, obtuse, protruding 6–7 mm from sepal appendices. Anthers ovate, hairy, with an appendix orange and almost triangular. Style c. 1 mm long, geniculate. Stigma globose. Capsules subrounded, c. 8 × 7 mm, slightly sulcate, opening at ripening into 3 valves, with 25–30 seeds. Seeds c. 2 × 1 mm, chestnut-brown; elaiosome covering c. 1/5 of seed.

Distributional Range: Endemic to the high-mountain zone of Tenerife, Canary Islands, Spain, where it is known from only two localities (Fig. 1). Locally common near the summit of Montaña Guajara (28°12'54″N, 16°36'44″W, 2600 m a.s.l.) with nearly 3000 individuals, but scarce (with only a few dozen individuals) at the second locality, Topo de la Grieta 3 km to the northeast (28°14'20″N, 16°34'17″W, 2300 m a.s.l.). 

Habitats: In general, the habitat is characterized by low or moderate slopes, with acid and rocky substrates sometimes mixed with pumice. These environments are subject to relatively strong winds (Wildpret & Martín 2005) and frequent winter frosts. Vegetation at the sites is dominated by a low mixed cushion-shrub community (Fig. 5) with Adenocarpus viscosus (Willd.) Webb & Berthel. subsp. viscosus (Fabaceae) one of the more common species. Other Canary Island endemics present are Erysimum scoparium (Brouss. ex Willd.) Wettst. (Brassicaceae), Nepeta teydea Webb & Berthel. (Lamiaceae), Sparto-cytisus supranubius (L. f.) Christ ex G. Kunkel (Fabaceae), and Tolpis webbii Sch. Bip. ex Webb & Berthel. (Asteraceae).

Conservation status.  Viola guaxarensis is known from only two localities with little more than 3000 individuals in total. Its extent of occurrence and area of occupancy are 28 km2 and 12 km2 respectively, calculated at a 2 × 2 km grid-cell size (IUCN Standards and Petitions Subcommittee 2017). Since the exclusion of introduced domesticated livestock (originally goats) from the area in the 1950s, the main threat factor (perhaps the only one) in the two known localities is the more recent abundance of other alien herbivores: mouflon introduced for hunting purposes, and rabbits. These browse the plants and may cause their death.

References:

1. Viola guaxarensis (Violaceae): a new Viola from Tenerife, Canary Islands, Spain Manuel V. Marrero Gómez, José L. Martín Esquivel, José R. Docoito Díaz, Manuel Suárez Izquierdo Willdenowia, 50(1):13-21 (2020). https://doi.org/10.3372/wi.50.50102