Type:— COSTA RICA. Guanacaste: Tilarán, Tierras Morenas, desviación a la izquierda después del Río Cabuyo, camino al Proyecto Geotérmico Tenorio y Cerro Jilguero, ca. 4.5 km norte de Tierras Morenas, ladera sureste del Volcán Tenorio, 10°36’11.6”N 85°00’05.3”W, 900–1000 m, bosque pluvial premontano, epífitas a orillas del camino y en bordes de potreros, 2 febrero 2006, Bogarín 2386 (holotype: USJ!; isotype: JBL-spirit!).

The fasciculate inflorescence with numerous simultaneously open flowers in Pleurothallis hawkingii is reminiscent of P. bothros Luer (1996: 70–72). It differs, however, in the non-spreading, pale yellow to whitish flowers with pinkish markings (vs. greenish), oblong synsepal (vs. ovate), obtuse petals (vs. acute) and lip horizontally disposed, panduriform, smaller, ca. 2.7 × 1.7 mm (vs. recurved, ovate, 3.5 × 2.5 mm).

Epiphytic, erect herbs, up to 35 cm tall. Roots flexuous, thin, 0.5–1.0 mm diameter, densely spaced, appearing fasciculate. Ramicauls erect, thin, up to 25 cm long, covered by tubular sheaths close to the base, tightly adpressed, up to 5 cm long. Leaves horizontal or nearly so, sessile, ovate, shortly acuminate, 8.0–9.5 × 3.0– 3.5 cm, deeply cordate. Inflorescence a fascicle of 3–9 simultaneously open flowers, subtended by a spathaceous bract 1.0– 1.5 cm long; pedicels terete, 5–6 mm long, pale green. Ovary clavate, 3.2–3.5 mm long, green. Flowers non-spreading, pale yellow with pinkish markings to solid pink; dorsal sepal oblong, slightly concave, obtuse, 3(5)-veined, 7.0–7.3 × 2.9–3.1 mm, apiculate; lateral sepals connate in an oblong, slightly concave synsepal, obtuse, 6-veined, 6.5–7.0 × 3.3–3.5 mm; petals oblong, oblique, acute, 3.5–3.7 × 1.1–1.3 mm; lip panduriform, horizontally disposed, 2.6–2.8 × 1.6–1.8 mm, margins raised, apex obtuse; glenion a depression between elevated lateral margins, the disk ca. 0.6 mm long; column straight, transversely subrectangular, with a column foot, 1.5–1.7 × 1.5–1.6 mm, the anther and stigma apical; anther cap ovate, cucullate, acute at the base, bilobed apically, 2-celled, ca. 0.7 × 0.5 mm; pollinia 2, narrowly ovate-pyriform, 0.7 mm long, connected to an elliptic viscidium. Fruits and seeds unknown.

Additional specimens examined:— COSTA RICA. Guanacaste: La Cruz, Parque Nacional Guanacaste, Estación Biológica Maritza, Volcán Orosí, cima del volcán entre el hito y la piedra, 1300 m, 10°58’48” N, 85°28’30” W, 21Agosto 2017 (fl), Morales, Grayum & Rojas 15521 (INB-CR); La Cruz, Parque Nacional Guanacaste, Estación Biológica Maritza, Volcán Orosí, cima del volcán entre el hito y la piedra, 1300 m, 10°58’48” N, 85°28’30” W, 21 Agosto 2017 (fl), Morales, Grayum & Rojas 15523 (INB-CR); La Cruz, Parque Nacional Guanacaste, Estación Biológica Maritza, Volcán Orosí, cima del volcán entre la base del campamento y sendero a Maritza, 1300 m, 10°58’33” N, 85°28’54” W, 23 Agosto 2017 (fl), Morales 15527 (INB-CR; Fig. 2).

Eponomy:—Honouring the English theoretical physicist, cosmologist and author Stephen William Hawking, who passed away the day this manuscript was submitted, 14 March 2018.

Phenology:—Flowering August in the field but January and February in cultivation.

Distribution:—Endemic to northern Costa Rica.

Habitat and ecology:—The species is only known from the Orosí Volcano and the Tilarán area in Cordillera de Guanacaste between 900–1300 m.

Notes:— Pleurothallis hawkingii belongs to P. sect. Macrophyllae-Fasciculatae (Luer 2005), and can be recognised by the fasciculate inflorescence of numerous simultaneously open flowers, a rare feature in this species-rich group. It shares the fasciculate inflorescence of several simultaneously open flowers with P. bothros and P. vide-vallis, also described in this paper. Pleurothallis hawkingii can be distinguished from P. vide-vallis by the oblong synsepal (vs. elliptic), narrower oblong (vs. elliptic) petals, horizontal lip (vs. apically recurved) that is shorter and broader (2.6–2.8 × 1.6–1.8 mm vs. 3.4–3.6 × 1.3–1.5 mm) and has raised margins, lacking a callus higher at the base. It is also found at lower elevations than P. vide-vallis.