Two new species of Trivalvaria (Annonaceae) from northern Myanmar

Abstract Trivalvaria rubra and Trivalvaria casseabriae, two new species of Annonaceae from Putao, Kachin State, Myanmar, are here described and illustrated. They are morphologically similar to T. costata and T. macrophylla. The major differences between them are outlined and discussed. A diagnostic key to the species of Trivalvaria is provided.


Introduction
Trivalvaria (Miq.) Miq. (Miquel, 1865) is a small genus with six species now recognised, which are mainly distributed in Indochina and Southeast Asia (Scheffer 1869, Das Debika 1968, Kessler 1993, van Heusden 1997, Li and Gilbert 2011, Chatrou et al. 2012. The genus belongs to the subfamily Annonoideae Raf. tribe Miliuseae Hook. f. & Thomson (Chatrou et al. 2012). The monophyly of Trivalvaria as well as its sister group relationship with Marsypopetalum Scheff., is confirmed with strong support; it was considered very close to Marsypopetalum and is characterised by morphological synapomorphies such as extra-axillary inflorescences, short pedicels (less than 1 cm long) and a single, basal ovule in each carpel and hence a solitary seed in each monocarp (Xue et al. 2011, Chaowasku et al. 2014. To date, there are currently two species Trivalvaria dubia (Kurz.) J. Sincl. and T. macrophylla Miq. recorded in Myanmar (Kress et al. 2003), the former now treated as a synonym of T. costata (Hook. f. & Thomson) I. M. Turner (Turner 2009).
Since 2014, repeated China-Myanmar joint field expeditions have been carried out to survey plant diversity in Northern Myanmar, specimens of Trivalvaria being found in Putao, Kachin state. Based on a detailed examination of the morphological and anatomical characters of the material and possible closely similar species (van Heusden 1997, Turner 2009, Gardner et al. 2015, it was concluded that the specimens collected in Myanmar belong to species new to science and these are hereby described and illustrated.

Material and methods
Measurements and morphological character assessments of the two possible new species Trivalvaria rubra and Trivalvaria casseabriae were examined based on dried specimens and fresh materials in field observations. They were compared with the morphologically similar species T. costata, T. macrophylla and T. nervosa, with affinities inferred using descriptions, type specimens and other herbarium specimens (van Heusden 1997, Turner 2009, Li and Gilbert 2011, Gardner et al. 2015. Protologues and images of type specimens were gathered from JSTOR Global Plants (http://plants.jstor.org). Conservation status evaluations of the new species were based on the International Union for Conservation of Nature guidelines (IUCN 2012).
Phenology. Flowering in May to June and fruiting occurs from June to December. Etymology. The species epithet refers to its pink flower. Distribution and habitat. Trivalvaria rubra is hitherto known from the type locality of Putao, Kachin state in Northern Myanmar, it is a small shrub that grows in the understory in tropical dipterocarpa forests, the dominant tree species are Shorea assamica, Dysoxylum mollissimum, Aglaia elaeagnoidea, Garcinia spp., Goniothalamus peduncularis, Antidesma spp., shrub species are Hymenandra wallichii, Ardisia sp., Zingiber sp., at an elevation of ca. 600-900 m a.s.l.
Conservation status. Trivalvaria rubra was collected on the way from Namti to Nahsihbo, Putao, Northern Myanmar, this area being difficult to travel due to its rugged terrain. At least three populations and ca. 60 individuals per population have been discovered. Currently, the locality is not legally protected and, although young individuals were recorded in field, the fragmented habitat and continuous logging severely threaten its survival. At present, it is suggested that it be considered as 'Vulnerable' (VU) on the basis of current IUCN Red List Categories and Criteria (IUCN 2012).
Specimen examined (  Diagnosis. Trivalvaria casseabriae is similar to Trivalvaria argentea in leaf shape, but can be distinguished by its larger flower size and outer petals equal to inner petals, petals 6-10 × 3-5 mm (vs. 2 × 3 mm), 2-2.5 times as long as wide and elliptic to ovate-elliptic.
Phenology. Flowering at May to July. Etymology. The specific epithet is derived from the abbreviation of Southeast Asia Biodiversity Research Institute, Chinese Academy of Sciences (CAS-SEABRI); noun in apposition. The name is dedicated to its three-part mission, viz., (a) Serve China's "the Silk Road Economic Belt and the 21st Century Maritime Silk Road" initiative; (b) Integrate efforts by CAS and international institutes to organise professional research groups and train researchers in Southeast Asian countries; and (c) Provide support to all domestic and international partners.
Distribution and habitat. Trivalvaria casseabriae is only known from the type locality of Putao, Kachin state in Northern Myanmar, where it grows in the understory of tropical montane broadleaf forests, the dominant tree species being Altingia excels, Dysoxylum spp., Garcinia spp., Elaeocarpus spp., at an elevation of ca. 700-900 m.
Conservation status. Although Trivalvaria casseabriae was collected on the way from Wasadam to Upper Shanhkaung, Putao District, Northern Myanmar, only one population and less than 50 individuals, has been discovered. Potential populations and more individuals may be found in future field surveys. Currently, the locality is not legally protected and, although young individuals were recorded in field, the fragmented habitat and continuous logging severely threaten its survival. At present, it is suggested that it be considered as 'Vulnerable' (VU) on the basis of current IUCN Red List Categories and Criteria (IUCN, 2012).

Discussion
Also as a genus, Trivalvaria was revised and mentioned by several experts (Heusden 1997, Gardner et al. 2015, but it is still poorly understood due to the very limited collections and poorly known taxonomic information. For this study, the authors have tried to combine the original description and field observations to present a brief approved taxonomic characters (Table 1).