Myrcia machinazana (Myrtaceae), a new Amazonian species from southern Ecuador

ABSTRACT Myrcia machinazana, a new species from southern Amazonia in Ecuador is described and illustrated; additionally a distribution map is presented and its conservation status and relationships with other species are discussed. This new species is similar to Myrcia gigantifolia, but differs by its reddish to dark-brown indumentum on new growth (vs. new growth glabrous in M. gigantifolia) and dense panicles with compactly arranged flowers and fruits (vs. panicles lax, flowers and fruits loosely arranged in M. gigantifolia). A key to the Ecuadorian species of Myrcia is provided.


Introduction
Myrcia DC., one of the largest genus of Neotropical Myrtaceae, occurs from Mexico, Central America, the Caribbean, to South America [1]. Molecular phylogenetic studies [2,3] suggest a broad circumscription (Myrcia s.l.), including, however, the distinctive genus Calyptranthes Sw. as a section. Myrcia, as we recognize it [1], comprises ca. 500 or more species. In Ecuador, they are characterized by the usually opposite leaves, trichomes simple or dibrachiate, inflorescences paniculate; calyx either open, with five free lobes or closed and tearing into irregular, deciduous lobes; petals usually five; stamens numerous; ovary usually twolocular, with two ovules per locule; stigma punctiform; fruits usually crowned by the calyx lobes; seeds 1 or 2, the seed coat membranous or carthaceous; embryo myrcioid, the cotyledons leafy and folded, the radicle elongate, equaling the cotyledons in length [1].
In Ecuador, 21 species of Myrcia have been recorded, seven of them are endemics, including this new species. The distribution of Myrcia in Ecuador ranges from 200 to 3000 m.a.s.l; its highest diversity is found in the southern province of Zamora-Chinchipe (10 species), followed by the central and north Amazonian provinces of Sucumbios, Napo, Pastaza and Orellana with six to nine species [1].
During recent botanical explorations in the Machinaza river basin, an undercollected area in the Zamora-Chinchipe province, we collected a new species of Myrcia with large leaves. We present a taxonomic description for this new species, images for all its structures, and a distribution map; additionally its conservation status and relationships with other species are discussed.

Materials and methods
Fieldwork: Recently, during floristic inventories carried out in October 2019 and February 2020 in the Fruta del Norte mining concession, Zamora-Chinchipe province, we were fortunate to obtain flowers and mature fruits and close-up pictures of all structures for this new species.
Identification and Morphological analysis: We consulted pertinent literature, specimens examined at F and QCA herbaria, and high resolution images of type material of Neotropical taxa (Tropicos database, https://www.tropicos.org/ [4] and the JSTOR Global Plants website http://plants.jstor.org [5]). Fresh material and pictures were the basis for the detailed morphological description of this species. All CONTACT Álvaro J. Pérez ajperezc@puce.edu.ec measurements were made in fresh, and fine observations and measurements of reproductive structures were made with the aid of a stereo-microscope. in M. gigantifolia) and dense panicles with compactly arranged flowers and fruits (vs. panicles lax, flowers and fruits loosely arranged in M. gigantifolia).

Distribution, habitat and ecology
Endemic to the Cordillera del Cóndor region, along the Machinaza river basin in Zamora-Chinchipe province. This species is known only from the type locality and surrounding areas along the road Los Encuentros -El Pindal -Campamento Las Peñas, at 1300-1500 m in elevation ( Figure 3). The habitat is a mature forest with low human intervention, where approximately 10 adult individuals were observed, but no seedlings nor juveniles. According to the Ministerio del Ambiente de Ecuador [6] this locality lies within a much larger zone dominated by evergreen low montane forest of the Cordilleras Cóndor-Kutukú ( Figure 4). According to the field observations, it grows associated with tree species, some of them endemics, including Brosimum utile (Kunth) Oken, locally known as sandi, Elaeagia mariae Wedd., named as barniz, Magnolia arroyoana Molinari and Magnolia yantzazana F. Arroyo, known as cucharillos, Graffenrieda spp., and the palms Euterpe precatoria Mart., Geonoma spp. and Socratea cf. salazarii H.E. Moore.
The Cordillera del Cóndor is a poorly explored region that extends ca. 150 km north to south from Ecuador to Peru. This mountain range is considered an eastern extension of the Andean chain that was uplifted ca. five million years ago. Biological explorations in this area have revealed a rich species biodiversity with high endemism. In particular, the region harbours many taxa disjunct with the Guiana Shield of northern South America due to their shared geology. Cordillera del Cóndor contains a high concentration of species new to science, and many are still to be discovered [7][8][9][10][11][12].

Etymology
The specific epithet refers to its type locality, in the forests surrounding the Machinaza river basin.

Phenology
This species has been collected flowering in January and sets fruits in October.

Conservation status
Following IUCN [13] criteria the status is Critically Endangered B1ab(i,ii,iii). The criteria justifying this classification include the species' small population size, with only 12 total known individuals, an estimated area of occupancy of 15 km 2 , continuously fragmented habitat due to land use change for mining activities. More exploration is needed to determine its real population size and the occupancy area.

Discussion
Myrcia machinazana belongs to sect. Myrcia due to the calyx with five distinct lobes and hypanthium  not prolonged above the ovary. Myrcia machinazana and M. gigantifolia are easily recognized from the other species of the genus by their unique giant leaves (longer than 30 cm and wider than 15 cm) with impressed venation [14]; in both species, the leaves are morphologically similar. These two species differ mainly in the reddish-to dark-brown indumentum on new growth (vs. new growth glabrous in M. gigantifolia) and dense panicles with compactly arranged flowers and fruits (vs. panicles lax, flowers and fruits loosely arranged in M. gigantifolia). Additionally, M. gigantifolia grows only in varzea forest along the Tiputini and Yasuní rivers, while M. machinazana grows on terra firme forest with loamy sandstone and granite soils. 5b. Leaf blades narrowly elliptic to elliptic; calyx lobes longer than wide, acute to obtuse.

Additional specimens examined. ECUADOR
6a. Leaf venation salient, but appearing strongly sulcate above, the midvein a narrow ridge; marginal veins 2, the innermost ca 3-5 mm from margins; leaf base obtuse to subcordate. M. crassimarginata McVaugh 6b. Midvein impressed above, the lateral and marginal veins plane to impressed above; marginal vein 1,