Philodendron luisae (Araceae), a new species from Rio de Janeiro State, Brazil

Philodendron is the second largest genus of Araceae, being highly diverse in the Atlantic Forest biome, with nearly one third of the Brazilian species occurring in Southern Brazil, particularly in Rio de Janeiro state. During a local inventory in Silva Jardim municipality, we found a peculiar population of Philodendron growing in lowland rainforest. After morphological analysis and comparisons with similar species, the population proved to be a new undescribed species of subgenus Philodendron section Macrobelium. The new species, named Philodendron luisae, is here described, illustrated and compared to morphologically close species.


Background
Philodendron Schott is the second largest genus of Araceae, with ca. 480 exclusively Neotropical species (Boyce and Croat 2014). The genus is highly diverse in tropical rainforests, such as the Atlantic Forest of coastal Brazil. Despite the elevated levels of deforestation in the Atlantic Forest (Fundação SOS Mata Atlântica -Instituto Nacional de Pesquisas Espaciais 2014), this biome accounts for ca. 12% of the genus diversity in its overall range and 40% of the genus diversity in Brazil ). These numbers are being constantly increased by the recognition of new species, especially from Southeastern Brazil (e.g. Buturi et al. 2014, Calazans and Sakuragui 2013, Coelho 2010, Gonçalves 2011. In Rio de Janeiro state, Southern Brazil, the genus is represented by an impressive number of species, despite the reduced geographical range and high levels of habitat fragmentation (Sakuragui et al. 2011). Of the 168 Brazilian species, 30 occur in the Rio de Janeiro state . Although efforts to catalogue the regional flora dates back to the eighteen century, many localities remain poorly known or even uncollected, especially outside the metropolitan area of the Rio de Janeiro City, justifying intensive sampling efforts.
Here we describe Philodendron luisae sp. nov., an only recently collected and recognized species from Rio de Janeiro State's lowlands.

Methods
During a flora inventory conducted in the Atlantic Forest remnants in Silva Jardim municipality, Rio de Janeiro State, we found an indeterminable Philodendron species. It was recognized as belonging to subgenus Philodendron section Macrobelium and analyzed through the two more comprehensive and updated keys of the section (Croat 1997, Sakuragui et al. 2005. The species was also compared with the type specimens and descriptions of morphologically similar species. The descriptive terminology follows Stearn (2004) and Mayo (1991). Morphological analyzes of fresh and dry materials were performed with the aid of a stereoscopic microscope. The extent of occurrence and area of occupancy were calculated using the GeoCAT tool (Bachman et al. 2011).

Phenology
Collected in flower in November.

Etymology
The species is named in memory of the Biology undergraduate student Luisa Pinho Sartori, who inspired the conservation and educational initiatives promoted by Sartori family.

Distribution and ecology
Only known from three records in reduced Atlantic Ombrophilous Dense Submontane Forest fragments in Silva Jardim municipality, a rural zone of Rio de Janeiro state (Figure 3). The species can be found in small patches of submontane and seasonally flooded forests in areas of regeneration, growing mainly in primary Tabebuia formations associated to the phorophytes Tabebuia cassinoides (Lam.) DC. and Dicksonia sp.. This is indicative of the species' tolerance to open habitats, which may be interesting in reforestation projects. The species is also frequently found growing together with P. nadruzianum Sakur.

Conservation
Our data so far indicate the species as critically endangered (CR) -B1ab (ii, iii, iv) -following the categories and criteria of International Union for Conservation of Nature (2012), with extent of occurrence estimated in 32.2 km 2 . In this category are inserted species facing a high risk of extinction in the wild, with extent of occurrence <100 km 2 and very fragmented, known from a single location, with continuing decline inferred for the number of individuals and habitat quality.
All records of P. luisae up to now are strongly related to stream margins, an area designated as permanently protected by Brazilian federal law in order to preserve the biodiversity and environmental resources in strategic areas. Additionally, the species is only known from particular properties within the Área de Proteção Ambiental da Bacia do Rio São João/ Mico-Leão-Dourado, a conservation unity of sustainable use (Ministério do Meio Ambiente -Instituto Chico Mendes de Conservação da  Biodiversidade 2008). The region suffered historical fragmentation due to selective extraction of timber and farming practices (Carvalho et al. 2006, Guedes-Bruni et al. 2006, however, the forest remnants are very representative of the Atlantic Ombrophilous Dense Submontane Forest, being of high priority for conservation (Carvalho et al. 2006 (Figure 3). Probably, populations of P. luisae may be found in the lowlands of this ecological corridor, assured within protected areas.
The association between P. luisae and the phorophyte T. cassinoides is interesting from the conservational viewpoint since this tree is currently threatened and listed in the Red List of the Brazilian Flora (Lohmann et al. 2013). The tree has suffered an intensive selective extraction due to its high quality timber, used mainly for the manufacturing of shoes (Lohmann et al. 2013). This activity probably caused impact on the natural populations of P. luisae in the Tabebuia formation, contributing to the fragmented distribution currently known.

Features and affinities
Philodendron luisae can be promptly recognized by its small and fragile leaves (often ripped when adult) and 3-4-angular, light brown colored stem. The overall leaf shape and inflorescence with apical sterile zone makes this species close to P. simonianum Sakur. and P. tenuispadix E.G.Gonç., but it differs by its longer internodes, smaller leaf blade, number of primary lateral veins, number of inflorescences per sympodium, absence of extrafloral nectaries and spathe features (Table 1). When the leaves are still young, P. luisae also resembles P. fragile Nadruz & Mayo and P. millerianum Nadruz & Sakur. by its triangular and fragile leaves without well developed posterior divisions, but the species show a number of differences between them (Table 1).
Moreover, among these related species, P. luisae is the unique known to grown in swamp forest, a vegetation formation frequently more open and exposed to seasonality than the humid and shaded forests where the most of Philodendron species occurs.

Conclusions
Philodendron luisae is a new species easily recognizable and well supported and represents the 31st species record for Rio de Janeiro State. The species, only known from one locality, exemplifies the importance and urgency of local and regional floras to a broaden knowledge of the Brazilian biodiversity.