Introduction

Viola L. is the most species-rich genus in the Violaceae, with 610–655 species distributed throughout most temperate regions of the world as well as on mountains and islands in the tropics (Marcussen & al. 2015; Watson & Flores unpubl. data). Marcussen & al. (2015) provisionally recognized 16 sections, but the genus is currently undergoing revision, the first one since the outline by Becker (1925), which may result in changes to the infrageneric classification (T. Marcussen pers. comm.).

Viola sect. Andinium W. Becker (Becker 1925) contains the largest number of known species (Marcussen & al. 2015; Watson & Flores unpubl. data), yet remains the least understood of the infrageneric divisions of Viola. Currently there are 100 published species accepted by the present authors (Watson & Flores 2018), excluding the novelty presented here, while 36 more have still to be described.

The longitudinal distribution of Viola sect. Andinium covers 7500 km when adjusted to follow the Andean chain, and is almost continuous. The equator marks the northernmost limit of its range, which reaches down as far as c. 47°S in Patagonia. Lateral distribution extends from the Pacific coasts of Chile and S Peru inland to the high Andes, reaching its maximum width of c. 700 km at around 25°S. Taxa in this section inhabit elevations from sea level to over 5000 m, but 88% of its species occur at Andean heights exclusively or predominantly (Watson & Flores 2014b; Watson & al. 2015). The centre of diversity of the section stretches from C Chile and Argentina to N Patagonia. Another lesser and more dispersed group covers the tropical Andean highlands of Ecuador, Peru and N Bolivia (Watson & Flores unpubl. data), while a third aggregation of 17 species, including the new Viola beati, exists in the outlying eastern cordilleras of NW Argentina (Watson & Flores 2014a).

In 2005, two of the present authors (J.M.W. & A.R.F.) visited the Botanischer Garten und Botanisches Museum Berlin (B) to review any remaining material of the heavily bomb-damaged Viola collection (Hiepko 1987; Haageman & Zepernick 1993). There we examined a pygmy Viola species, which had been collected in NW Argentina in 1994. Notes and sketches were made and a full investigation revealed that the species described below was indeed unknown to science.

Material and methods

The present conclusive outcome is based on the study of herbarium material at B. Detailed measurements and descriptive notes were taken there in 2005 with the aid of a Wild M5A binocular dissecting microscope. Inflorescences and flowers were soaked in tap water and boiled in order to be softened, and close-up photographs showing various aspects and micromorphological details were taken, using an Olympus SZX16 (Fig. 1A–F).

Results

Viola beati J. M. Watson & A. R. Flores, sp. nov. – Fig. 1. Holotype: Argentina, Provincia Catamarca, Departmento Belén, hills at summit of first pass on Ruta Nacional 43, 54 km by road travelling north from Ruta Nacional 40 (28 km NNE of Villavil), 26°51′S, 66°45′11″W, 3350–3400 m, 20 Feb 1994, B. E. Leuenberger, S. C. Arroyo-Leuenberger & U. Eggli 4263 (B 10 0630577!  http://herbarium.bgbm.org/object/B100630577).

Diagnosis — The new species belongs in Viola sect. Andinium W. Becker, where it is apparently closely allied only to V. singularis J. M. Watson & A. R. Flores. It differs from that species by stipules being absent, lamina with abaxial surface eglandular and margin with fewer (3 vs 5 or 6) crenations, and inferior petal conduplicate and deeply naviculate. Uniquely for the section, V. beati also possesses a ligneous aerial structure and porrect, paddle-shaped style crest lobes.

Description — Herb, perennial, ligneous-cauline, cushion-forming chamaephyte, c. 2 cm high × 3.5 cm in diam.; indumentum where present always long, pale silky-silvery, villous, flattened trichomes. Lower subterranean rootstock unknown; caudex remnant (as present on holotype specimen) vertical, undivided, c. 7 mm long × c. 2 mm in diam., ligneous, containing sparse leaf scars of previous growth, radiating at ground level into regular branching; stem 14–20 mm long × c. 0.35 mm thick, simple or few-branched, bare basally for 7–12 mm, terminating apically in dense subrosettes 5–8 mm high × 10–14 mm in diam. Leaves somewhat thick-textured but not rigid, cryptic; main lower mature leaves petiolate, 5–8 mm long, occasional leaves subtending rosettes sessile, c. 1.5 mm long; upper juvenile leaves shorter and with pre-developed petiole; stipules absent; petiole 3.5–5.8 mm long × c. 0.2 mm wide in mature leaves, somewhat channelled beneath, glabrous; mature lamina 1.5–2.2 × 1–1.5 mm, obovate to oblanceolate, tapering to petiole, apex subacute to subobtuse; adaxial surface reticulate-alveolate, greyish to pale grey-brown; abaxial surface subrugose, with dense indumentum when juvenile, less so at maturity, eglandular; margin thickened, crenate, on both sides with 2 large, rounded main lobes and 1 smaller, somewhat forward-curved basal lobe, crenation less pronounced in lowermost mature leaves; marginal indumentum irregularly directed, denser in basal part and sparse along subglabrous apex of mature leaves. Flowers solitary from leaf axil, produced level with leaves or slightly recessed; peduncle somewhat shorter than mature leaves, indumentum present in distal ⅔, dense apically, becoming glabrous toward base; bracteoles c. 5.25 mm long, inserted in basal ½ of peduncle, narrowly linear, tapering to point, hyaline, subglabrous basally, indumentum present on distal ¹/4. Calyx 5–6 mm long; sepals c. 0.8 mm wide at base, linear-triangular, hyaline margin curved and terminating below thickened, acuminate apex; margin and abaxial surface densely covered with irregularly directed indumentum. Corolla c. 4.5 mm long, white or pale violet, with violet staining distally on superior and lateral petals, where terminating below in longitudinal central vein; lowermost petal with extensive fine violet veining, at least at apex; superior petals c. 4.5 × 0.8 mm, linear, glabrous, apex rounded; lateral petals c. 4 × 1.8 mm, proximal ⅔ oval, distal ⅓ a slightly narrower triangular extension, indumentum present on face, forming dense, central patch, apex rounded; inferior petal somewhat porrect, notably larger in area than superior four, c. 4 × 6 mm (when flattened), broadly obcordate, conduplicate, deeply navicular and distinctly carinate, glabrous; spur not visible on holotype specimen, but evidently either much reduced and contained within apical curve of peduncle or absent. Style surrounded and covered basally to 1.6 mm in diam. by conjoined anthers and dull, dark yellow connectives; style head globose, directed downward and somewhat outward, terminated by anterior stigmatic aperture; stigma wide, blunt; style crests 2, lateral, porrect, curved, concave, paddle-shaped lobes c. 0.8 mm long on both sides of style head and exceeding stigmatic aperture. Fruit (as seen in immature stage) a capsule containing c. 4 seeds; submature seeds c. 1.7 × 1.2 mm, pyriform, chestnut-brown.

Phenology — Flowering in February.

Fig. 1.

Viola beati, holotype specimen – A: lateral view of whole aerial formation of plant; B: flower in natural position among foliage; C: lateral view of flower showing strong navicular conduplication of lowermost petal; note also atypical size imbalance between that and higher four petals; D: frontal view of flower opened and flattened, resulting in splitting and separation of lowermost petal sides; E: basal stamens, connectives (yellow), apex of style, and lateral lobes of style crest directed forward and covering stigma; F: lateral view of immature seed. – All photographs by Monika Lüchow.

Distribution and ecology — Apparently endemic to high ridges to the north of Belén, Catamarca Province, Argentina (Fig. 3 & 4) as one small population of a few individuals in exposed sandy to loose, gravelly ground at the foot of a hillslope (Fig. 2). Dominant vegetation consists of a mixed bunch grass and low to cushion shrub community with intermittent clearings and more extensive open stretches. Other immediate Andean taxa include Airampoa soehrensii (Britton & Rose) Lodé [syn. A. ayrampo (Haenke) Doweld] (Cactaceae), Caiophora coronata Gillies ex Hook. & Arn. (Loasaceae), Glandularia cf. microphylla (Kunth) Cabrera (Verbenaceae), Phacelia pinnatifida Griseb. ex Wedd. (Boraginaceae) and Trichocline exscapa Griseb. (Asteraceae). As noted in situ by the collectors, the rosettes of V. beati were at soil level, with their leaves tightly arranged and greyish tomentose.

Conservation status —Known only from the type collection, made in 1994; it was not found by the present authors in Argentinian herbaria or at any other institution visited. Although under no apparent immediate threat, as a small population confined to an extremely restricted area, it classifies as a very rare, potentially endangered, single-site microendemic.

Eponymy — The epithet commemorates and hon-ours the late Dr Beat Leuenberger, who was a botanist at the Botanischer Garten und Botanisches Museum Berlin and husband of the present author Silvia Arroyo-Leuenberger. He is the first and so far only person to have found this species. The personal name Beat possesses a well-established latinized form, Beatus, meaning “blessed”. Therefore, and in accordance with Rec. 60C.1 of the International Code of Nomenclature for algae, fungi, and plants (Turland & al. 2018), the correct orthography of the epithet is the genitive of Beatus, i.e. beati, with a single “i”. Art. 60.8 does not apply in this case.

Remarks — Heavy pressing of specimens can lead to some or all of the diagnostic adaxial lamina reticulation being partially or completely reduced to a flat, smooth surface, as has occurred with the type of Viola beati. This may give rise to inaccurate descriptions and lead to subsequent taxonomic confusion (e.g. Rossow 1988).

The existence or not of a lower petal nectar spur remains unresolved due to the undesirability of risking damage to the delicate floral structure of this unique specimen by dissection. It may either be concealed and very short, as in other species of the section (pers. obs.), or absent. One allied species only, Viola granulosa Wedd., does lack this feature (Weddell 1864; Baehni & Weibel 1941).

Fig. 2.

Locality and environment of Viola beati – A: general situation on pass to north-northeast of Villavil, Catamarca, Argentina at 3400 m, 20 Feb 1994; B: same area as A, showing vegetation with sandy clearings as habitat of V. beati, 20 Feb 1994. – Both photographs by Urs Eggli.

Viola singularis is noted here as the only species bearing any significantly close morphological resemblance to V. beati, as well as being nearest to it geographically. Nicola (2017) treated the former species as doubtfully present in the flora of Argentina. This judgement was based on the grounds that the holotype is the only known individual of the species, its overall morphology had been impossible to assess, and its authors had noted its similarity to other taxa of V. sect. Andinium (Watson & Flores 2009). This assessment, which could also be largely applied to V. beati, lacks foundation because critical characters that distinguish V. singularis from all others in the section, including V. beati, are clearly defined both in the type description (Watson & Flores 2009) and the present work. Furthermore, the known existence of only one representative of a taxon is not by itself a scientifically valid reason to dispute its acceptance as a distinct entity.

Fig. 3.

Known distribution of Viola beati (red circle) in southern cone of South America. Coordinates are distorted by projection curvature and angle of alignment of map. – Google Earth ( https://www.google.com/earth/), modified by John Watson and BGBM Berlin.

Discussion

Evolution, ecology and phytogeography

Viola sect. Andinium has evolved over a calculated period of c. 30 million years (Marcussen & al. 2015) in a context of continuous Andean orogeny involving violent volcanic activity (Luebert & Weigend 2014). Due to ceaseless and at times rapid resultant geological and climatic transformations throughout their range, an abundance new habitats has continually been available for these opportunist, short- and long- distance Viola colonizers. But without doubt, wide-scale extinctions, both instantaneous and gradual, have also occurred (Watson & Flores 2013).

Although the date of origin of Viola beati is not known, that of another species of the proposed V. volcanica alliance within V. sect. Andinium has been revealed by molecular analysis. As noted above, the section itself is calculated to have appeared c. 30 million years ago (mya), while V. congesta Gillies ex Hook. & Arn., considered on morphological evidence to be a relatively evolutionarily advanced member of the V. volcanica alliance (Watson & Flores unpubl. data), dates back to c. 10 mya (Marcussen & al. 2015; T. Marcussen in litt.). This extensive timescale, taken in conjunction with the 4000 km range of the V. volcanica alliance and the unstable geological setting of its development, provides a background explanation for both the unique morphology and lack of apparent close allies of V. beati apart from V. singularis as assumed here. The possibility that shared morphology of the latter two species has arisen through reticulation should be taken seriously (Marcussen & al. 2015).

Fig. 4.

Viola beati type locality (red circle) in Catamarca Province, Argentina, with area containing type locality of V. singularis (cyan ellipse). – Google Earth ( https://www.google.com/earth/), modified by John Watson and BGBM Berlin.