Stelis machupicchuensis (Orchidaceae), a new species from S Peru

Abstract: Stelis machupicchuensis Collantes & C. Martel, from the cloud forest of Cusco, Peru, is proposed as a new species. The new species is similar to S. antennata Garay, from which it differs in the oblique subpentagonal-trullate petals, pentagonal-subtrullate lip and subquadrate to suborbicular callus. A description, illustrations and taxonomic account are provided. Citation: Collantes B., Farfán J. & Martel C. 2017: Stelis machupicchuensis (Orchidaceae), a new species from S Peru.— Willdenowia 47: 167–172. doi: https://doi.org/10.3372/wi.47.47208 Version of record first published online on 25 August 2017 ahead of inclusion in August 2017 issue.


Introduction
Stelis Sw. is a highly diverse neotropical genus of Or chidaceae belonging to the subtribe Pleurothallidinae. It currently includes somewhere between 900 species in its narrowest circumscription (Stelis s.str.; Luer 2007Luer , 2009) and 1100 species in its broadest circumscription (sensu Pridgeon 2005;Karremans & al. 2013;Karremans 2014Karremans , 2015. Species of Stelis are distributed from Mexico to Central America and the Caribbean, and from Venezuela to Bolivia and Brazil, but the greatest diversity is found along the cordilleras of the Andes (Solano-Gómez 2014).
In Peru, there are 150 recorded species of Stelis s.l. (Brako & Zarucchi 1993;Ulloa Ulloa & al. 2004;Rodríguez & al. 2006;Collantes & Karremans 2017), 139 of them belonging to Stelis s.str. Species of this group are characterized by a short column, which is surrounded by remarkably short petals and a lip, which Luer (2016) has denominated the "central apparatus". However, a few species of Stelis s.s. do not present this feature, and the petals and lip are quite conspicuous (e.g. S. antennata Garay).
During field trips to the cloud forest of Cusco Department, in the SE Peruvian Andes, specimens of a remarkable, apparently undescribed Stelis taxon were col-lected. It is proposed here as a new species and formally described and illustrated.

Material and methods
Specimens of the new taxon were collected during field work in the cloud forest of Machu Picchu Historical Sanctuary and Wayqecha Biological Station (Cusco Department, Peru), during 2004 and 2016, respectively. Collected material was pressed and dried or preserved in spirit. Further revision of fresh specimens was carried out in Machu Picchu and Wayqecha during 2016. The line drawings and figures were prepared from preserved specimens using a Leica Wild M8 stereomicroscope, a Canon A-1 camera with a Canon FD 50mm f/3.5 lens, and an HP Deskjet 2050 scanner. Herbarium specimens were deposited at USM (herbarium Code according to Index Herbariorum: http:// sweetgum.nybg.org/science/ih/. The software DIVA-GIS (Version 7.5) was used to prepare the distribution map. Diagnosis -The new species is similar to Stelis anten nata Garay but differs in the broadly elliptic lateral sepals (vs broadly ovate lateral sepals in S. antennata), oblique subpentagonal-trullate petals (vs subpentagonal-rhombic petals), pentagonal-subtrullate lip (vs subquadrate, moderately unguiculate lip) and subquadrate to suborbicular callus (vs moderately unguiculate callus).
Phenology -Flowering was observed between January and May.
Distribution and ecology -This species is known only from the cloud forest of Cusco Department, in the SE Peruvian Andes, between 2600 and 2800 m (Fig. 3). The plants grow on branches and trunks of live and dead trees in primary cloud forests.
Conservation status -Up to now, Stelis machupicchu ensis is known from only two localities. Few individuals (genets consisting of several ramets) have been found in Machu Picchu and Wayqecha Biological Station (upper side of the Kos ñipata basin) and both subpopulations may comprise fewer than 250 mature individuals. According to the IUCN Red List (IUCN 2017), the species can be categorized as Endangered (EN), criterion D, based on the number of mature individuals.
Etymology -The name honours the Machu Picchu Historical Sanctuary, where the species was first discovered.
Remarks -Flowers of plants from Machu Picchu bear 3-veined petals, whereas those from Wayqecha are 1-veined. Furthermore, the sepals, petals and lip of flowers from Wayqecha present laterally reflexed edges (Fig.  2C). Stelis machupicchuensis presents flowers with tailed, long acuminate petals (more than half the length of the sepals), a character observed in few Stelis s.str. species [e.g. S. antennata, S. barbellata Luer & Hirtz and S. miranda Luer & R. Escobar;Luer (2016)]. Stelis machupicchuen sis is most similar to S. antennata, with which it shares a similar general morphology of the petals and column (Fig.  4). However, it is easily distinguishable in the pentagonal-subtrullate lip and subquadrate to suborbicular callus. Both S. antennata and S. machupicchuensis occur sympatrically in Machu Picchu and Wayqecha Biological Station.