A new Muscarella (Orchidaceae: Pleurothallidinae) from Tapantí National Park, Costa Rica

A new species of Muscarella from Costa Rica, is described and illustrated. Muscarella tapantiensis most resembles M. coeloglossa but differs in the longer pedicels (3-5 vs. 1-2 mm), the shorter (2.5-2.8 vs. 3.75 mm), connate (vs. free) lateral sepals, and the lip with triangular (vs. broadly rounded) lower lateral lobes. Muscarella xanthella also resembles M. tapantiensis; however, it differs in the successively flowered raceme with alternate pedicels, the deeply fimbriate petals and the thick, rounded lip with densely verrucose lateral lobes. We provide illustrations, etymology, notes on ecology, pictures of the plants and habitat, and a distribution map of the new species. We discuss the inclusion of this species in the genus Muscarella.


INTRODUCTION
A fundamental principle of any study aimed at understanding the specific relationships among different organisms is to identify them correctly. This simple rule becomes critical and unpractical when the research is carried out in a tropical, biologically-rich region (Higgins and Ruokolainen 2004). Biologists esteem that, in the tropics, only about 86% of life diversity has been apprehended by science, and the degree of the average knowledge may vary among living groups (Mora et al. 2011).
With over 50,000 ha, Tapantí-Macizo de la Muerte National Park (TNP) is one of the largest protected areas in Costa Rica (Sánchez 2002;Bernard et al. 2009) and one of the species-rich spots for orchids in the country (Pupulin 2003;Pupulin and Bogarín 2012;Crain and Fernández 2020). Because of this high diversity and the ease to reach the park within less than two hours from the capital city of San José, ongoing floristic, ecological and bio-geographical projects have been carried out by Lankester Botanical Garden and scientific partners for almost two decades (Pupulin 2001;, Pupulin et al. 2009Pupulin and Bogarín 2012). In 2015, a long-term research project led by Dr. Jyotsna Sharma from Texas Tech University was initiated to understand if mycorrhizal fungi distribution and specificity influence the distribution of epiphytic orchid species in a community. The massive numbers of co-occurring species there ( Figure 1) offer a unique opportunity to test the limits of the species co-existence hypothesis. As part of required taxonomic identification of the epiphytic orchid species subjected to fungal analyses in the study site, a species of Muscarella Luer proved impossible to match with any previously described taxon.
Muscarella is a Neotropical genus of the Pleurothallidinae with around 50 species ranging from Mexico to Brazil and the Antilles (Luer 2006;Pessoa et al. 2014). The genus is distinguished by the cespitose plants with loose racemes, f lowers with long-tailed sepals and fringed, fimbriate or denticulate petals, and a thick, fleshy lip that is somehow ciliate (Luer 2006). Most species bear longitudinal calli, and the column-foot is variously concave (Luer 2006). The species of Muscarella were initially treated under Pleurothallis R.Br. and later into a broad concept of Specklinia Lindl. (Pridgeon et al. 2001). Lindley (1830) described Specklinia to include minute, herbaceous plants with flowers of gibbose sepals, free petals and a labellum a third length of the sepals, and membranaceous, winged columns. However, Garay (1974) transferred it to the subgeneric level under Pleurothallis. Then, Luer (1986) built ten sections within Pleurothallis to group species with similar floral features, including a section of minute flowers with thick, fringed or verrucose, lobed lips, which he named Pleurothallis section Muscariae Luer (1986). Later, Pridgeon et al. (2001) proposed a broad concept of Specklinia, sister to the Platystele-Scaphosepalum clade, for small plants with an abbreviated stem with an annulus, flowers with sepals connate to different degrees, a lip hinged to the column foot, and a column provided with a toothed apex and ventral anther and stigma. They based their findings on initial molecular phylogenies of the subtribe. The concept included species of Pleurothallis sections Hymenodanthae Barbosa Rodrigues (1882), Muscariae Luer, and Tribuloides Luer (1986) and species from Acostaea Schltr. (Schlechter 1923), Empusella Luer (Luer 2004) and Pseudoctomeria Kraenzl. (Kraenzlin 1925).
Finally, Luer (2006) considered the new circumscription of Specklinia as a polyphyletic aggregation of many taxa; thus, he proposed the transfer of section Muscariae (Luer 1986) to genus Muscarella. The genus is a monophyletic and morphologically discernible group from the rest of Specklinia, and it is supported by the most recent molecular phylogenetic studies in the Pleurothallidinae Muscarella comprises 11 species in Costa Rica, including the species proposed here as new (Luer 2006;Ossenbach et al. 2007). We describe it hereafter.

MATERIALS AND METHODS
We collected living specimens at TNP, Cartago, Costa Rica, and cultivated them in the collections at Lankester Botanical Garden (JBL), University of Costa Rica. Living plants were documented with sketches using a Leica® MZ9.5 stereo-microscope with a drawing tube. The sketches were digitalized, and the images were used for diagramming a draft composite template in Adobe Photoshop® CC. Photographs were taken with a Nikon D7100, Nikon Bellows PB-6 extension, and a Nikon AF-D 50 mm f/1.8 lens. Descriptions were prepared from both living specimens and herbarium material deposited at JBL. Locality data were obtained with a Garmin eTrex Vista GPS and supporting maps and recorded along with phenology observations in a computerized database at JBL. Ecological zones follow the Holdridge Life Zone System (Holdridge 1967, Holdridge 1987. Distribution maps were made using the geographic information system software ArcView GIS 3.3 (ESRI, California, USA). Specimens were preserved in formaldehyde: acetic acid: ethanol [FAA (53% ethanol, 37% water, 5% formaldehyde, and 5% glycerol)].

Etymology
After Tapantí National Park, the place where plants of this species were first collected.

Distribution and habitat
Only known from Costa Rica, growing on mossy twigs, mostly of Saurauia montana (Actinidiaceae), in open areas along or close to riparian premontane wet and rain forests of the Caribbean watershed of the Talamanca mountain range (Figure 3).

Flowering time
Plants were seen in flower in the wild from October to April. At TNP, a flowering peak occurs between November and January.

DISCUSSION
The new species is recognized by the small, less than 3 mm in diameter, translucent yellow-greenish to pinkish flowers with concave sepals, fimbriate and aristate petals, and a lip with two short lateral lobes, characters that agree with the concept of Muscarella. The new species most resembles the Ecuadorian Muscarella coeloglossa (Luer & Hirtz) Luer, but differs from it by the longer pedicels (3-5 mm in M. tapantiensis vs. 1-2 mm), the shorter (2.5-2.8 vs. 3.75 mm), connate (vs. free), apically acuminate (vs. rounded) lateral sepals, and the lip with triangular (vs. broadly rounded) lower lateral lobes. The Ecuadorian Muscarella xanthella (Luer) Luer also resembles M. tapantiensis, mostly because of the more or less elliptic leaves and the small pinkish flowers with concave, translucid sepals. Nevertheless, Muscarella xanthella produces a fasciculouslike inflorescence with pedicels congested at the apex of the peduncle, different from the successively flowered raceme with alternate pedicels of M. tapantiensis. When looking closer to the flower, the lacerate petals of Muscarella xanthella differ from the deeply fimbriate ones of M. tapantiensis, and the lip is thick, rounded with densely verrucose lateral lobes. In contrast, Muscarella tapantiensis bears thinner, triangular lobes at the base and is papillose mostly at the base.