A new Viola (Violaceae) from the Argentinian Andes

Abstract: Viola beati, a hitherto unknown species of V. sect. Andinium (Violaceae) is described and illustrated. It is an inconspicuous, diminutive, perennial forb currently known from only one locality in NW Argentina. We draw attention to its morphology, ecology, rarity and endemism. The differences between V. beati and its apparently only close relative, V. singularis J. M. Watson & A. R. Flores, are defined.


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 cov-36 Watson & al.: Viola beati from the Argentinian Andes ers 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). 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, paddleshaped style crest lobes.

Phenology -Flowering in February. Willdenowia 49 -2019
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) lectors, 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 com memorates and honours the late Dr Beat Leuenberger, who was a botanist at the Botanischer Garten und Bota nisches 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).
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.

Infra-sectional affiliation
The most recognizable common feature of the new species is the network of raised veins on the adaxial lamina surface, which unites an otherwise fairly disparate and very widely distributed complex of Viola sect. An dinium species under the provisional grouping of the Viola volcanica Gillies ex Hook. & Arn. alliance (Watson & Flores unpubl. data). Beyond that, its precise systematic relationships are unclear, but morphologically it is significantly different from all taxa presumed to be closely related to it except the even smaller V. singularis (Fig. 3 &  4). Originally, the latter species was presumed on available evidence to be situated 500 km to the south of V. beati (Watson & Flores 2009). Subsequently, it was accurately located at a mere 10 -15 km distant from V. beati across a valley in the same mountain ridge (Watson & Flores 2014b) (Fig. 4). Despite this geographical proximity, shared morphology is limited to their perennial, dwarf, cryptic life-forms; long "true" petioles; and laminas with crenate margins and reticulate-alveolate venation. Other diagnostic features, such as style crest, leaf outline, corolla configuration and presence or not of glands, are either only broadly comparable or differ entirely.  (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).