Taxonomic studies on Begonia (Begoniaceae) in Myanmar I: three new species and supplementary description of Begonia rheophytica from Northern Myanmar

Abstract Three new species of Begonia (B. chenii, B. putaoensis and B. crassitepala) belonging to Begonia section Platycentrum and a supplementary description of B. rheophytica with a detailed description of female flowers from Putao, Kachin State, Northern Myanmar, are described and illustrated. All the new species are endemic to Northern Myanmar and can be easily distinguished from other species among the section Platycentrum. A detailed description, photographs, habitat, distribution and a comparison with the most related allied species for all new species are provided.


Introduction
Begonia Linnaeus (1753: 1056) (Begoniaceae) is one of the largest genera of angiosperm in the world, comprising more than 1900 species (Hughes et al. 2015), currently divided into 70 sections (Moonlight et al. 2018). The genus consists of herbs or lianas and is distributed throughout the tropical and subtropical regions of the world (Doorenbos et al. 1998;Moonlight et al. 2018). It has around 959 species and 19 recognized sections in Asia with the bulk occurring in Southeast Asia (Doorenbos et al. 1998;Shui et al. 2002;Ku et al. 2007;Hughes 2008;Moonlight et al. 2018). According to a recent updated checklist of Begonia from Myanmar by , 73 species of Begonia have been recorded from Myanmar.
During floristic surveys of northern Myanmar from 2016 to 2018, some interesting Begonia specimens were collected. After conducting a detailed examination of the morphological characteristics of the collected material, reviewing the type specimens and taxonomic publications, the authors have confirmed that the specimen of Begonia collected from northern Myanmar belong to species new to science, which are described and illustrated below.

Material and methods
Measurements and morphological character assessments of the new species have been examined based on fresh materials and dried specimens. They have been compared with morphologically similar species by affinities inferred using descriptions (Ku et al. 2007, Camfield and and type specimens in herbaria (BM, E, K, NYBG, KUN, PE, HITBC and RAF). Protologues and images of type specimens were gathered from JSTOR Global Plants (http://plants.jstor.org).  dots on the upper surface, but significantly differs by stipules slightly pilose (vs. glabrous), petiole densely reddish pilose (vs. sparsely puberulous), 6 (rarely 4 or 7) tepals of female flower (vs. 4 tepals) and red, 3 or 4 locular ovary (vs. green, 2 locular).
Phenology. Flowering from April to May; fruiting from May to June. Distribution. The species is only known from the type locality, Putao District, Kachin State, Northern Myanmar.
Ecology. The species grows in the moist shaded environment of tropical rain forest, elevation about 512 m.
Etymology. The species epithet "chenii" is named after Professor Chen Jin, the director of Southeast Asia Biodiversity Research Institute, Chinese Academy of Sciences, who gave us the opportunity to study the Myanmar flora, which led to the discovery of this new species.
Conservation status. Data Deficient (DD). Begonia chenii was collected along the path on the way from Putao to Upper Shankhaung where any signs of major anthropogenic disturbance were noticed in the type locality. However, further explorations are needed for a proper assessment of conservation due to insufficient information on its distribution and population status. Therefore, the species has been preliminarily assigned to Data Deficient (DD) category according to The Guidelines for Using The IUCN Red List Categories and Criteria (IUCN 2017).
Distribution. The species is known from the single locality in Putao District, Kachin State, Northern Myanmar.
Ecology. The species grows on moist rocky slopes of tropical montane forest, elevation 500-900 m.
Etymology. The species epithet refers to the type locality of the species, Putao District, Kachin State, Northern Myanmar.
Conservation status. Data Deficient (DD). The species might not confront strong human pressures because of the remoteness of its type locality. But we cannot assess the species' risk of extinction due to lack of data. Therefore, the species is temporarily assigned a status Data Deficient (DD) according to The Guidelines for Using The IUCN Red List Categories and Criteria (IUCN 2017).
Phenology. Flowering from June−July; fruiting from July−August. Distribution. Endemic to the type locality, Putao District, Kachin State, Northern Myanmar.
Etymology. The species epithet refers to its thick tepals. Ecology. In the tropical montane forest up to about 577 m elevation, on the moist soil slope.
Conservation status. Data Deficient (DD). Begonia crassitepala have been collected along the roadside from Langsa to Gawlaw village where no signs of major anthropogenic disturbance were noticed. Further exploration is required to access the current range of the species (IUCN 2017).

Begonia rheophytica
Distribution Note. This species was originally described by  from the male flowering plant only. Here, we provide a supplementary description of B. rheophytica with a detailed monograph of female flowers from Putao, Kachin State, Northern Myanmar.