Zinowiewia sebastianii (Celastraceae), a new high-Andean species from the Colombian Eastern Cordillera

Zinowiewia sebastianii, a new species from high-Andean forests of the Eastern Cordillera at the department of Boyacá (Colombia) is described and illustrated, and its taxonomic affinities are discussed. Individuals of the new species are shrubs to 5 m tall, with interpetiolar, laciniate stipules, leaf blades with 8–11 pairs of lateral veins and entire, plane margin, 2-forked dichasia to 1 × 1 cm, axillary to the distal leaves, calyx, corolla and androecium pentamerous or tetramerous, and two-celled, one-seeded samaras 18–20 × 5–7 mm. Based on the low number of individuals of Z. sebastianii observed within an area of occupancy < 10 km2, in severely fragmented forests, the species is proposed as Critically Endangered (CR), as it faces an extremely high risk of extinction in the wild.


INTRODUCTION
The genus Zinowiewia (Celastraceae) comprises 17 species distributed from Mexico to Peru.Five species are known to occur in South America, primarily in the northern Andes, extending to the Sierra Nevada de Santa Marta (Colombia), and the Cordillera del Norte (Venezuela).The species of Zinowiewia are noteworthy in having samaras with one apical wing (Fig. 1g, i, j, l), a trait found in the New World Celastraceae only in the genera Plenckia, from Bolivia, Brazil, and Paraguay, and Rzendowskia from Mexico (Simmons andHedin 1999, Simmons 2004).Samaras in the family appear to have evolved independently several times (Simmons et al. 2001, Simmons et al. 2012).Most of the species of Zinowiewia are large (> 20 m tall) trees sometimes with buttressed trunks, and have minute pentamerous flowers arranged in dichasial cymes (Figs. 1, 2;Turczaninow 1859, Lundell 1939a, Edwin and Ding Hou 1975, Ulloa-Ulloa and Jørgensen 1994, Simmons 2004, Barrie 2015).Despite Z. concinna has been reported as a secondary dominant tree in Mexico at about 2100 m in elevation (Vásquez and Givnish 1998), individuals in the remaining species from South America are rare and scattered, with very low densities in lowland to montane forests.
After a 30-year period following the morphology and phenology of the population from the department of Boyacá (Colombia), located between 2750 and 3000 m in elevation, the first author (FG) has consistently found a set of diagnostic characters that does not match those of any of the known species of the genus, including Z. australis.These characters are related primarily to the habit, the leaf venation, the order of branching of the inflorescence, the floral merosity, and the size and morphology of the samara.Additionally, the population is located above 2750 m in elevation, isolated from the remaining South American species, which reach up to 2000 m at the nearest spots in Colombia (Fig. 3).The new species here described is the only South American taxon that reaches high-Andean Quercus forests.

MATERIAL AND METHODS
The terminology used for the descriptions follows primarily Jackson (1900) and Hickey and King (2000).The taxonomic schemes followed here for the species of Zinowiewia are primarily those presented by Ulloa-Ulloa and Jørgensen (1994) for the South American species, and Barrie (2015) for the Mesoamerican species currently recognized.The type specimens of all Zinowiewia species were consulted through Jstor (https://plants.jstor.org/).In addition, all specimens of Zinowiewia deposited at the Herbario Nacional Colombiano, Universidad Nacional de Colombia (COL), the Herbario de la Universidad de Antioquia (HUA), and the Herbario de la Universidad del Valle (CUVC) were examined.

Geographic distribution and elevation
Colombia (Boyacá  Marín-Corba and Betancur (1997).These authors confirmed the extremely low number of individuals, and the low density and frequency and dominance values of Z. sebastianii.
After extensive field work by various researchers during the last 60 years in the Natural Reserve where the new species grows, only a few individuals of Zinowiewia sebastianii have been observed in the region (six observed by the senior author in a 30 yr period), within an area of occupancy < 10 km 2 , in severely fragmented forests.Altogether, these criteria render the new species as Critically Endangered (CR), as it faces an extremely high risk of extinction in the wild.
Zinowiewia sebastianii has been collected in flowers and fruits in March, June and August.

Figure 1 .
Figure 1.Zinowiewia sebastianii (González 4644).a. Apex of a flowering branchlet.b. detail of lower leaf surface.c. detail of petiole and dichasium.d-g.Fully developed dichasia; note tetramerous flowers (arrows) in d and g. h.Detail of a tetramerous flower.i-k.Late gynoecium elongation and samara formation.l.Samaras; note the 2-forked dichasia when fully developed and fruit set.m.Transverse section through the base of a samara showing the fertile, one-seeded locule (arrow) and the vestigial locule (asterisk).n.Seed.Scale bars: 5 mm in a, b, i; 2 mm in c-g, l; 500 µm in h, j, k, m, n.

Figure 3 .
Figure 3. Map of distribution of the species of Zinowiewia in Colombia.

Table 1 .
Comparison between the new species and the remaining South American species of Zinowiewia.