Goniothalamus saccopetaloides Y.H. Tan & Bin Yang, a new species is described and illustrated from Laos. This species shows morphological similarities to G. yunnanensis W.T. Wang, but it differs from the latter by having almost fleshy, involute and saccate outer petals, subglobose monocarps, and single seeded monocarps. Goniothalamus cheliensis, and G. calvicarpus are new records for the Flora of Lao PDR. A key to Goniothalamus species indigenous to Laos is provided here.

Goniothalamus, Laos, field survey, new species, new record

Goniothalamus (Blume) Hook.f. & Thomson, comprising over 130 species of trees and shrubs, are one of the largest palaeotropical genera in the Annonaceae, mainly distributed from India and Sri Lanka to tropical Australia and the South Pacific Islands (Saunders and Chalermglin 2008; Nakkuntod et al. 2009; Turner 2014; Thomas et al. 2017). The genus is characterized by flowers with two whorls of petals of which the inner petals are smaller than the outer ones; three inner petals form a distinctive mitriform dome over the reproductive organs acting as a pollination chamber (Saunders and Chalermglin 2008; Tang et al. 2015), and stamens with apical connectives. Although the genus Mitrephora J. D. Hooker & Thomson also shares these similar features, Goniothalamus can be distinguished easily by its linear-oblong stamens, inner petals each with a short claw or stipe (Li et al. 2011). The genus shows considerable diversity in flowers of different size and shape, hairy indumentum, and color usually cream, yellow or red at maturity, and fruit morphology, with fruit of different size and shape (Saunders and Chalermglin 2008; Tang 2014; Tang et al. 2015). Species of the genus are widely distributed in tropical South-East Asian lowland and submontane forests (Tang 2014). Several Goniothalamus species have been described in recent years, including four new species from Thailand (Saunders and Chalermglin 2008), four new species from Borneo (Turner and Saunders 2008), and a new species from Palawan, the Philippines (Tang et al. 2013). In Laos, Goniothalamus are represented by four species (Newman et al. 2007; Lee 2016), i.e., Goniothalamus laoticus (Finet & Gagnep.) Bân, Goniothalamus repevensis Pierre ex Finet & Gagnep., Goniothalamus marcanii Craib and Goniothalamus saigonensis Pierre ex Finet & Gagnep., whereas the latter two were respectively treated as synonyms of Goniothalamus tamirensis Pierre ex Finet & Gagnep. (Saunders and Chalermglin 2008) and Goniothalamus gabriacianus (Baill.) Ast (Li et al. 2011).

In recent years, the authors examined the flowering material of Annonaceae cultivated in the living collections of Xishuangbanna Tropical Botanical Garden (XTBG), Chinese Academy of Sciences (CAS) and found an unknown species, which is very distinctive and belongs to the genus Goniothalamus; the records showed that this accession was originally collected in 2002, from Lao PDR (although the exact location remains unknown). Based on the morphological characters, we compared it to all other currently known species and concluded that it is new to science. As part of the botanical inventory of China-Laos transboundary biodiversity conservation, we carried out floristic surveys in the Nam Ha National Biodiversity Conservation Area in Luang Namtha Province and Phou Hin Phee National Biodiversity Conservation Area in Oudomxay Province of the northern Laos. During the fieldwork in March and October of 2018, we encountered two species of Goniothalamus representing new records for the flora of Laos. Therefore, the new and noteworthy species of Goniothalamus from Laos are provided and updated in this study.

Our study of the new taxon was predominantly based on plant material newly collected in XTBG. The records showed that this accession was originally collected in 2002, from Laos, although the exact location remains unknown. Ten individuals cultivated in two living collections were observed. Morphological characterizations were measured in the field. We compared our samples with type specimens of similar species deposited in herbaria. Specimens of Goniothalamus from Laos and neighboring regions were examined from the following herbaria: HITBC, IBSC, SING, A, K, BK, high-resolution digital images of specimens (especially types) from JSTOR Global Plants (https://plants.jstor.org/) and other virtual herbarium websites (http://www.cvh.ac.cn/), as well as the taxonomic literature for species identification.

The authors cordially thank staff of the Biotechnology and Ecology Institute (BEI), Nam Ha National Biodiversity Conservation Area in Laung Namtha Province and Phou Hin Phee National Biodiversity Conservation Area, Oudomxay province of Lao PDR for their support of field works in the protected area. We are grateful to Dr. Liang Song, Dr. Hua-Zheng Lu, Dr. Su Li, Mr. Ren Li, Mr. Xiao-Dong Zeng, Ms. Zhong-Li Gan and Ms. Dong-Li Quan for their kind help in the field. This research was funded by Lancang-Mekong Cooperation (LMC) Special Fund (Biodiversity Monitoring and Network Construction along Lancang-Mekong River Basin project) and the CAS 135 program (No. 2017XTBG-F03), and the project of the Southeast Asia biodiversity research institute, Chinese Academy of Sciences (Y4ZK111B01).