Matelea tarrazuana (Apocynaceae, Asclepiadoideae), a new critically endangered ocellate species from Central Pacific of Costa Rica

Matelea tarrazuana, a new species endemic to Costa Rica, is described and illustrated. It is similar to M. pusilliflora, a vine from Yucatan Peninsula because of its green flowers with a reflective white spot in the apex at the apex of each lobe, but differs from that species by its longer pedicels, larger corolla lobes, staminal corona purple (vs. orange), gynostegium with the style apex purple (vs. green) and inhabiting premontane forests of Costa Rica. Data on its distribution and habitat, phenology, conservation status and taxonomy are included, as well as photographs of the living plant, and a key to identify the five related species in Mesoamerica.


INTRODUCTION
Matelea Aub. (Asclepiadoideae) is one of the largest genera within Apocynaceae comprising approximately 225 species worldwide (McDonnell 2014). It comprises herbaceous or woody neotropical vines (Stevens 2009, Cortez et al. 2018, Morales & Stevens 2020, and is the largest genus in the New World subtribe Gonolobinae (G. Don.) Liede. (McDonnell 2014). It has been suggested that it has two centers of diversity: one includes southern Mexico-Guatemala, and the other in the north of South America (Spellman andDwyer 1973, Villaseñor 2016).
Molecular studies have suggested that Matelea sensu Woodson (1941) is morphologically heterogeneous and not monophyletic (Krings et al. 2008;Morillo 2015). Here we follow the concept of the genus Matelea according to Stevens (2009). Traditionally, Matelea has a mixed indumentum of long, short and glandular hairs, the glandular always colored, extra-axillary inflorescences, rotate or campanulate corollas, staminal corona fused to the base of the corolla or the gynostegium, and horizontal or subhorizontal pollinia laterally excavated and sterile near the union with the caudicle (Stevens 2009).
Matelea has been studied twice recently in Costa Rica. Stevens (2009) suggest that the genus has 13 species, whereas Morales & Stevens (2020) recognized 15 species. Because of this, it was unexpected to find a new species of this group. This taxon is unusual and conspicuously different in floral morphology from the other related species of Matelea in Mesoamerica, and belongs to a the "ocellate complex" (Krings 2012) characterized by its small-flowered species held together primarily by having a bright white reflective ocellus at the tip of each corolla lobe. Stevens and Arbelaez (2014) discusses the rarity of this group, and this new species reinforces the discussion and make the discovery more expected.

MATERIALS AND METHODS
The study area is located in the Zona de los Santos region (Tarrazú canton) in the Central Pacific of Costa Rica. The material was processed and incorporated into CR and USJ. The acronyms of herbaria mentioned in this work follow Thiers (2021). The description and illustration were based on live and dried material. Stevens (2009) and Cortez et al. (2018) were followed for the morphological terminology. Ecological life zone is described according to Holdridge et al. (1971). The assessments of the conservation status were made based on the guidelines of the International Union for Conservation of Nature (IUCN 2001), using parameters such as number of locations, extent of occurrence (criterion B1) and area of occupancy (criterion B2). Map was made using Photoshop.

Diagnosis
Similar to Matelea pusilliflora L.O. Williams in having leaves ovate with the base slightly cordate or truncate, inflorescences racemose and congested and flowers green with a reflective white spot in the apex of each lobe, but differs from that species by its pedicels 0.4-0.6 cm long (vs. 0.1-0.2 cm long), corolla lobes as long as wide, 0.4-0.5 cm long (vs. wider than long, 0.2-0.3 cm long), staminal corona purple (vs. orange), and gynostegium with the style apex and stigma purple (vs. green).

Etymology
This species is named after Tarrazú, locality of the type specimen.

Distribution and habitat
Matelea tarrazuana is endemic to Costa Rica. It is known only from the type locality, in primary and secondary forest in San Joaquín de Tarrazú, Zona de los Santos region, San José province, at 1249 m in a premontane rain forest (Figure 3).

Phenology
Flowering has been recorded in March during dry season, and November during rainy season. It was also observed in bloom during April, May, and July but no vouchers were prepared. No fruits were seen.

Conservation Status
Matelea tarrazuana is not protected in any protected state area or private reserve in Costa Rica The two specimens in herbaria and the single known population severely affected by unsustainable agricultural and livestock activities suggest that this species is rare. Despite to has a restricted natural distribution, the Data is Deficient (DD).

Remarks
Matelea tarrazuana is easily to recognize because of the reflective white spot in the apex of each corolla lobe, a diagnostic characteristic that share with M. corniculata, M. emmartinezii, M. pusilliflora, and M. ocellata   with the style apex and stigma purple (vs. green) ( Figure  4). Diagnostic morphological characteristics to separate these species are given in Table 1.
Three morphological characters are peculiar in this species: the apparent lack of latex, the position of the leaves according to the type of stem and the progressive increase in size in the leaves in the plagiotropic stems. Morales & Stevens (2020) suggest species of Matelea in Costa Rica has latex, thus Matelea tarrazuana could be the only species of the genus in Costa Rica without latex. Furthermore, there is no documentation of the change in phyllotaxy depending on the type of stem in Matelea nor in the progressive size of the leaves. This species has an opposite-decussate leaves in orthotropic stems and opposite-distichous in plagiotropic stems (branches), and the leaves increasing progressively in size in the branches from the proximal to distal nodes. These three observations could be focused of taxonomic study in future studies of the group because they can represent important characters to differentiate species or clades.
This new species proposed here was found in a remnant forest surrounded by paddocks and especially coffee plantations. Unfortunately, the Zona de los Santos's region has been slowly deforested by coffee plantation in the last decades in less than one year, other three new and narrowly endemic species were published from this area (Cedeño et al. 2020, Juárez & Morales 2021. Mate-lea tarrazuana is the sixteen species of the genus documented for the country.