A new rare and endemic species of Sloanea (Elaeocarpaceae) from the Chocó region of Ecuador

Abstract A new species collected in the lowland forests of the Chocó region of Ecuador, Sloanea cayapensis, is described and illustrated and its morphological similarities with other species of Sloanea are discussed.


Introduction
The genus Sloanea L. is the second largest within the family Elaeocarpaceae and comprises approximately 200 species in the tropics and more than 120 species in the Neotropics (Smith 1954;Smith 2001;Sampaio 2009). Smith (1954) proposed that the centre of diversity for this group is the northern portion of the Amazon basin, including the Guiana Shield, but the genus is as diverse in Central and Western Amazonia as in the previously mentioned region (Castañeda 1981;Boeira 2010).
The most recent taxonomic study of Sloanea in Ecuador revealed that 25-30 species of the genus occur in the country (Jaramillo 2003, Pennington andWise 2017) and this number has increased with recent new descriptions (Guevara Andino et al. 2016;Guevara Andino et al. 2017). The genus is very diverse in Amazon lowland forests and in the Chocó forests on Ecuador's Pacific coast. As the southernmost extension of Colombia's Chocó forests, Ecuador's coastal Chocó is strikingly diverse (Gentry 1982) but remains poorly studied, despite several new species of the genus having been recently described (Palacios-Duque 2004a, b, 2005.

Materials and methods
We describe a new species of Sloanea from the Ecuadorian Chocó region, based on an analysis of morphological characters from material deposited in four Ecuadorian herbaria: the Herbario de la Pontificia Universidad Católica del Ecuador (QCA), Herbario Nacional del Ecuador (QCNE), Herbario Alfredo Paredes (QAP) and Herbario Amazónico del Ecuador (ECUAMZ). We also compared the new species with images of type specimens deposited in JStor and reviewed voucher specimens in the virtual herbaria of the Field Museum (F), the New York Botanical Garden (NY), the Herbario Nacional de Colombia (COL) and the Herbário do Instituto Nacional de Pesquisas da Amazônia (INPA); herbaria abbreviations follow Thiers 2016. In this work, we used the sub-generic classification developed by Smith (1954) for the circumscription of the new taxa. Earlier works have demonstrated that a single diagnostic character, the position of the calyx in relation to the bud, is the only consistent character in the group and may be considered diagnostic for the circumscription of taxa to the subgenus level (Sampaio 2009;Guevara Andino et al. 2016). Diagnosis. Sloanea cayapensis resembles S. grandiflora Smith and S. fragrans Rusby, the most morphologically similar taxa, but can be differentiated from them by having short petioles (2-7.5 cm), obovate-spatulate leaves, 6-8 free sepals, shorter thick and acute-obtuse anthers (1.5-2 mm), densely hirsute filaments and styles and by having capsules with large, flexible, curled bristles (2.8-6 cm).
Conservation status. Sloanea cayapensis may be catalogued as Endangered (EN) following IUCN (2012) criterion A2c, which indicates: "An observed, estimated, inferred or suspected population size reduction of ≥ 50% over the last 10 years or three generations, whichever is the longer, where the reduction or its causes may not have ceased or may not be understood or may not be reversible" and criterion B1ab(iii), which indicates: "Extent of occurrence (EOO) estimated to be less than 5,000 km 2 and estimates indicating continuing decline, observed, inferred or projected, in area, extent and/or quality of habitat". The analysis using the GeoCat tool for geospatial conservation assessment determined an EOO of 2000 km 2 (Bachman et al. 2011). Sloanea cayapensis is only known from two localities on the banks of the Cayapas River, in the lowland evergreen forest of the Equatorial Chocó. The area has suffered extensive clearcutting in the last 30 years, leading to a drastic reduction of native forests and expansion of oil palm plantations and illegal logging, these being the major threats faced by the species. Since collection of the types in 2003, no other specimens of this species have been recorded despite the fact that subsequent field trips have sampled the same habitat occupied by this species. Over the last 26 years, the annual rate of deforestation in the lowland evergreen forest of the Equatorial Chocó in Ecuador has been 1.7-2.9% and the remnant forests in this area cover just 24% of their original extent (Sierra 2013). Consequently, the habitat occupied by this species in Ecuador has been drastically reduced. However, the species is likely to occur in similar habitats in the Colombian Chocó where the dynamic of deforestation is less drastic but a cause for concern.
Sloanea cayapensis is distinguished from S. grandiflora in having a densely hirsute style (vs. glabrous style at the apex and slightly pubescent at the base), thin connective (vs. very wide connective between the anthers sacs on the abaxial surface), thick and obtuse anthers (vs. linear-lanceolate) and an ovoid and densely hirsute ovary with 4 locules (vs. pubescent ovary with 4-6 locules). It also differs from S. grandiflora in having lanceolate stipules (vs. navicular stipules with finely dentate margins), shorter pedicels (4-11 mm vs. 7-25 mm) and strongly ascendant numerous secondary veins (11-20 vs. 13-15 slightly ascendant secondary veins).