Introduction

Pleurothallis R.Br. (^{Brown 1813}) is one of the most diverse genera in terms of species richness of orchids within the subtribe Pleurothallidinae. It can be found in Central America and some countries of South America with more than 500 species described to date (^{Karremans & Vieira-Uribe 2020}, ^{Luer 1986}, ¹⁹⁸⁹, ¹⁹⁹⁸, ¹⁹⁹⁹, ²⁰⁰⁵), and Colombia is the country with the most recorded species of Pleurothallis, with 247 species (^{Bernal et al. 2016}, ^{Karremans et al. 2023}, ^{Ministerio de Ambiente y Desarrollo Sostenible y Universidad Nacional de Colombia 2015}).

The members of the Pleurothallis subsection Macrophyllae-Fasciculatae Lindl. (^{Lindley 1859}, ^{Luer 1986}) are identifiable mainly by their sessile leaves with a typically cordate base, flowers arranged in a fascicle, lateral sepals connate into a synsepal that is somewhat similar to the dorsal sepal, a bilobed stigma, and a lip lying on or slightly elevated above the synsepal (^{Luer 2005}, ^{Sierra-Ariza 2023}, ^{Wilson et al. 2018}).

Here, we describe and illustrate a new species of Pleurothallis subsection Macrophyllae-Fasciculatae from the Tropical Moist Forest from Valle del Cauca Department in the Western Andes of Colombia, morphologically similar to a diverse group of species with small yellow flowers up to 3 cm long and cordate leaves.

Materials and methods

The description and drawings were prepared from living specimens and flowers preserved in 70% alcohol. Flowers were dissected, measured, and photographed using Celestron Handheld Digital Microscope Pro. Vegetative structures were measured from dried material and reproductive structures from spirit material. Digital images were taken with a Nikon D750 and a Nikon 105mm f/2.8 macro lens. Sketches from living and preserved specimens were digitized, and the images were used for diagramming a draft composite template in Adobe Photoshop® CS6. A digital composite line drawing was then made (lines and stippling) in Procreate illustration application for iPad 6^th generation tablet computer (^{Bogarín et al. 2019}). The new species was described following the botanical terminology by ^{Beentje (2010)} and ^{Stearn (1992)}. All original descriptions of related species were consulted for detailed comparisons (^{Luer 2005}). We consulted specimens from the following herbaria: AMES, COL, CUVC, HUA, JAUM, JBB, VALLE, CAUP and MO (online), and no additional material of the new species was found.

Taxonomic treatment

Pleurothallis celsia Gal.-Tar. & J.S.Moreno sp. nov. (Fig. 1-2).

TYPE: COLOMBIA. Valle del Cauca: Municipio de Buenaventura, represa del Alto Anchicayá, Parque Nacional Natural Farallones de Cali, 976 m, 23 May 2020. R. GalindoTarazona 1463 (holotype: CUVC). (Fig. 1-2)

Diagnosis: Pleurothallis celsia is most similar to Pleurothallis folsomii (Luer & Endara) J.M.H.Shaw from which it can be distinguished by having a 3-veined dorsal sepal (vs. 5-veined) and most notably by its lip, which is widely ovate, the surface and margin pilose and papillate, with the base of the glenion densely vesiculose (vs. ovate, the surface smooth and the margins serrate, the base of the glenion smooth).

Plant epiphytic, caespitose, erect to suberect, 15.6-23.0 cm tall. Roots slender, up to 0.64 mm in diameter. Ramicauls 12.4-19.8 cm long, with a tubular sheath on the lower third and two other sheaths at the base, the sheaths papyraceous, light brown. Leaf coriaceous, ovate, acuminate to long acuminate, 7.8-8.2 × 3.85-3.95 cm, the base deeply cordate. Inflorescence a fascicle of successive flowers, up to 4 simultaneous flowers, enclosed at the base by a spathaceous bract ca. 1.07 cm long; peduncle terete, 1.86-2.61 mm long; floral bract tubular, papyraceous, acute, 5.11-6.98 mm long. Pedicel terete, 7.7-8.35 mm long. Ovary verrucose, terete, longitudinally sulcate, 4.36-4.69 mm long. Flowers with the perianth yellow. Sepals, membranaceous, glabrous. Dorsal sepal, lanceolate, obtuse, 7.21-9.18 × 2.98-4.22 mm, 3-veined, the veins carinate on the adaxial surface. Lateral sepals connate into an ovate, acute synsepal, concave at base, 6.08-7.83 × 4.39-5.34 mm, 6-veined. Petals, linear, falcate, the surface and margin pilose, acute, 3.43-4.85 × 1.06-1.25 mm, 1-veined. Lip, fleshy, widely-ovate, rounded, the surface and margin pilose and papillate, 2.06-2.83 × 1.76-2.54 mm, 3-veined, central lip shallowly concave at the base of the glenion, the glenion obovate, the base with two rounded and elevated, pronounced lobes, densely vesiculose. Column, short, semiterete, 1.04-1.20 mm long, with a short foot, thick; stigma apical, bilobed. Anther cap yellow-cream, apical, obovate, papillose, 0.85 × 1.67 mm. Pollinia two, obovoid.

Eponymy: In honor of the energy company CELSIA, that has contributed to the exploration, description, and conservation of the flora, in particular, orchids, in the Farallones de Cali National Natural Park in collaboration with the National Park, Universidad del Valle, and other institutions of the region. The epithet is used here as a noun in apposition.

Distribution and ecology: Pleurothallis celsia was discovered and described as an epiphyte of secondary vegetation along the edge of the roads (Fig. 3) in the western slope of the Western Cordillera, near a hydroelectric dam within the National Natural Park Farallones de Cali, where the species might be very well protected, due to the access for the general public being highly restricted (^{Moreno et al. 2020}).

Discussion

Pleurothallis celsia (Fig 4A) belongs to a group of species with similar, concolorous yellow flowers that mainly differ by the number of veins in the sepals and the shape and indumentum of the petals and lip. The new species is morphologically most similar to Pleurothallis folsomii (Fig. 4B) from Panama as mentioned in the diagnosis, but is also similar to Pleurothallis carduela (Luer) J.M.H.Shaw (^{Shaw 2016}) (Fig. 4C) from Ecuador (^{Luer 2005}), a species that is characterized by having a 7-veined dorsal sepal (vs. 3-veined), minutely denticulate margin of the petals and smooth indument (vs. margin and indument pilose) and the lip elliptical (vs. broadly ovate) with the indument and the margin denticulate (vs. indument and margin pilose and papillate).

A. Habit. B. Flower. C. Dissected perianth. D. Lip and column lateral view. E. Lip, adaxial and abaxial views. F. Anther cap and pollinia.

Illustration by J.S.Moreno based on the type.

Figure 1 Pleurothallis celsia Gal.-Tar. & J.S.Moreno. 

A. Habit. B. Flower. C. Dissected perianth. D. Lip and column lateral view. E. Lip, adaxial and abaxial views. F. Anther cap and pollinia.

LCDP by J.S.Moreno.

Figure 2 Pleurothallis celsia Gal.-Tar. & J.S.Moreno. 

A. Leaf and flower, front side. B. Flower. C. Habit and growth, in situ.

Photographs by J.S.Moreno (A, B) and R. Galindo-Tarazona (C).

Figure 3 Pleurothallis celsia Gal.-Tar. & J.S.Moreno. 

A. Pleurothallis celsia B. Pleurothallis folsomii (Luer & Endara) J.M.H.Shaw. C. Pleurothallis carduela (Luer) J.M.H.Shaw.

The white arrows show the margin and surface of the lip and petals of the three species.

Photographs by J.S. Moreno (A), M. Wilson (B) and Rudy Gelis (C).

Figure 4 Most similar species to Pleurothallis celsia Gal.-Tar. & J.S.Moreno.