Two new endemic species of Monstera (Araceae: Monsteroideae: Monstereae) from Golfito in southern Costa Rica

. Monstera croatii M.Cedeño & A.Hay and M. gambensis M.Cedeño & M.A.Blanco (Araceae: Monsteroideae: Monstereae) are newly described and illustrated from cantón Golfito in the Pacific lowlands of southern Costa Rica. Notes are provided on how they can be differentiated from similar species. Monstera croatii is unique in the genus because it reaches its adult vegetative morphology while growing as a terrestrial plant on the forest floor, and climbs only to a very limited height before flowering. Monstera gambensis is one of the smallest species in the genus.


INTRODUCTION
In Costa Rica there are some 24 genera and 256 species of Araceae (including subfamily Lemnoideae, commonly treated as a separate family), the most well-represented of the genera being Anthurium Schott, Philodendron Schott, and Monstera Adans. (Grayum 2003;Ortiz et al. 2018). These groups are abundant and diverse in very humid lowland forests and in cloud forests (Grayum 2003). Monstera is a genus that consists mostly of nomadic vines (sometimes referred to as hemi-epiphytes, but see Zotz 2013), and is best known for its often conspicuously perforated leaves (Grayum 2003;Cedeño-Fonseca et al. 2018;Hay 2019). Molecular-phylogenetic analyses of subfamily Monsteroideae agree in finding Monstera to be a monophyletic genus most closely allied to the tropical Asian genus Amydrium Schott and some (but not all) species of the likewise Asian Epipremnum Schott, and it is the only neotropical member of the pantropical tribe Monstereae or 'Rhaphidophora clade' (Tam et al. 2004;Zuluaga et al. 2019). It is considered one of the taxonomically most poorly understood aroid groups in Mesoamerica (Madison 1977;Croat 1992;Jácome and Croat 2002;Grayum 2003). The most recent taxonomic revision (Madison 1977) recognized 22 species in the entire genus. However, the first author's current research, revising Monstera for Central America, indicates that there are more than 40 species in this region alone (Cedeño-Fonseca 2019), with an as yet undetermined number of further species from Mexico, tropical South America, and the Caribbean.
The genus is currently divided into four sections -Echinospadix Madison, Marcgraviopsis Madison, Tornelia (Gutiérrez ex Schott) Madison, and Monstera (Madison 1977;Mayo et al. 1997;Croat et al. 2010)though it is doubtful whether this infrageneric classification will stand up to molecular analysis (e.g., Zuluaga et al. 2019). Section Monstera includes, among others, several small, mainly South American species -Monstera obliqua Miq. (Costa Rica to Ecuador, Perú, Venezuela, the Guianas and Brazil), M. xanthospatha Madison (western Colombia), and M. minima Madison (Panama and Colombia) (Madison 1977;Jácome and Croat 2002) -and during recent fieldwork in the forests of La Gamba, Golfito, a new diminutive species was collected, which is described and illustrated here. In addition, a species with terrestrial (or near terrestrial) habit was also collected in Golfito, which only ascends on the phorophyte to about 1.5 m above ground level. This species has also proven to be undescribed, and is named here. It too belongs to sect. Monstera sensu Madison (1977).  (Figures 1, 2).

Diagnosis
Monstera croatii is recognized by its terrestrial or very low nomadic-vining habit, petioles glaucous at the base, with the sheath extending to about half the total length, the sheath margins involute, and the free portion terete, greyish-glaucous leaf blades, adult leaf blades deeply pinnatifid, peduncles with a persistent mucronate cataphyll, and spadices with more or less spherical basal sterile flowers.

Etymology
The new species is named for Dr. Thomas B. Croat (MO), the leading authority on neotropical Araceae. He also realized that some herbarium specimens of this spe-  cies, previously identified as M. pinnatipartita Schott, could represent a different, undescribed species.

Distribution and habitat
Monstera croatii is endemic to Costa Rica, where it is known only from the south on the Pacific side in the region of Golfito and the Parque Nacional Corcovado (both in the cantón of Golfito) at ca. 300-600 m, in primary and secondary forest and in open areas ( Figure 6).

Phenology
Immature infructescences recorded in February; flowering observed in October and November.

Conservation status
Monstera croatii is protected in the Refugio Nacional de Vida Silvestre Golfito and in the Parque Nacional Corcovado.

Notes
Monstera croatii is differentiated from all other Costa Rican species of Monstera by having pruinose/glaucous stems and petioles, the petioles sheathing for about half their length, with the sheath wings involute and persistent and the free (distal) part terete or only weakly channeled. It is further differentiated by the deeply pinnatifid and bluish green leaf blades, sometimes with bifid lobes, and the pruinose peduncles with a persistent sheathing mucronate cataphyll. A unique characteristic of this species is its terrestrial habit, reaching the adult vegetative stage in this state and climbing only to very limited height before flowering. Fertile terrestrial individuals were not found, but one plant was observed fertile after climbing only 50 cm above ground level with the same stem and leaf morphology as terrestrial examples. Monstera croatii has sterile f lowers with the ovary spherical, as is also the case in M. glaucescens Croat & Grayum, which too has glaucous stems and briefly sheathed petioles, but that species (known only from the Caribbean side of Costa Rica) has the leaves pinnately lobed (never deeply pinnatifid), the petiolar sheath persistent but not with involute margins, and the non-sheathing part of the petiole channeled (never terete). Monstera croatii can also be confused with Monstera pinnatipartita, but that species has the petioles green or speckled (never glaucous), never develops to the adult vegetative form on the ground, is fertile only after significantly ascending its phorophyte, and has acuminate and marcescent (not mucronate and persistent) cataphylls.  (Figures 3, 4, 5).

Diagnosis
Monstera gambensis is recognised by its small entire leaves with or without fenestrations, and its asperous petioles with involute sheath margins that appear whitish. Similar in size to Monstera obliqua, it differs from that species by having asperous (vs. smooth) petioles, with the sheath margins persistent (vs. completely deciduous), and smaller leaf blades (12-24 × 5-10 cm, vs. ca. 35 × 14 cm).

Etymology
The epithet gambensis refers to the type locality.

Distribution and habitat
Monstera gambensis is endemic to Costa Rica, where it has been found growing low on the supporting trees (ca. 2 m above ground level), in rain forest at La Gamba Biological Station, cantón Golfito, mostly at 50-100 m. (Figure 6).

Phenology
Flowering has not been observed. An infructescence was recorded in May.

Conservation status
It is protected at the La Gamba Biological Station, the only known locality for this species.

Notes
Monstera obliqua, a species whose type is from Surinam and which in its current, broad conception extends into Amazonia, is known in Costa Rica only from the southeastern corner of the country (Grayum 2003), while the Costa Rican endemic M. gambensis is known only by a single collection from La Gamba, Golfito. Monstera gambensis is one of the smallest species in the genus, together with M. obliqua and M. minima. The latter, with smaller petioles (2-6 cm), leaf blades (9-14 × 2-4 cm), and spadices (ca. 4.4 × 09-1 cm) even smaller than those of M. gambensis (Jácome & Croat 2002), is only known from the northern (Caribbean) coast of Panama and along the Pacific slope of northern Colombia, in the Chocó region (Jácome and Croat 2002). In Costa Rica, M. gambensis is found in lowland tropical wet forest at elevations of up to ca. 100 m. The individuals observed were climbing in the undisturbed forest on small trees no more than 2.5 m high, with abundant shade in the understorey. Most adult leaves of Monstera gambensis are not fenestrated, but occasionally leaves are produced with up to two perforations, close to each other on the same side of the blade near its middle part. The measurements for the flowers of M. gambensis given above were taken from flower remnants of a single fruiting spadix, so they should be interpreted with caution. ACKNOWLEDGMENTS Marco Cedeño-Fonseca thanks the Organization for Tropical Studies for a Glaxo-Wellcome research grant and the Rexford Daubenmire fellowship, which supported fieldwork for the project "Taxonomy of the genus Monstera (Alismatales: Araceae) for Costa Rica", and an Alwyn H. Gentry Fellowship from the Missouri Botanical Garden and a Mini-ARTS Fellowship from the Society of Systematic Biologists, which allowed him to study herbarium material at the Missouri Botanical Garden, the Marie Selby Botanical Gardens, and the New York Botanical Garden. Michael Mittermeier, Cristina Goettsch Mittermeier, and Caroline Sparks also helped in raising funds for travel through a Gofundme.com campaign. Director Adam Karremans and the staff at the Jardín Botánico Lankester of Universidad de Costa Rica are thanked for allowing the cultivation of living plants. Isler Chinchilla and Gustavo Rojas-Alvarado are thanked for their help in the field. Two anonymous reviewers are thanked for their insightful suggestions that greatly improved the manuscript. We are grateful to the Ministerio de Ambiente y Energía de Costa Rica (MINAE) and its Sistema Nacional de Áreas de Conservación (SINAC) for issu- ing the scientific permits under which wild specimens were collected. This contribution represents part of the Master's thesis of Marco Cedeño-Fonseca, completed in the Programa de Posgrado en Biología at Universidad de Costa Rica.