﻿A new species of Argyreia (Convolvulaceae) from Yunnan, China

﻿Abstract Argyreiasubrotunda, a new species from Yunnan Province, China, is described and illustrated. The new species resembles A.fulvocymosa and A.wallichii, but differs from these in the flowers with an entire or shallowly lobed corolla, as well as smaller elliptic bracts, lax flat-topped cymes and shorter corolla tubes. An updated key to the species of Argyreia from Yunnan province is also provided.


Introduction
Argyreia Lour., a genus comprising scandent shrubs or lianas, is mainly distributed throughout tropical Asia (Staples and Traiperm 2017). Argyreia species mainly inhabit open and sunny places such as roadsides, thickets, and edges of mingled forest (Fang and Huang 1979;Fang and Staples 1995). The number of Argyreia species has been increasing and is now up to 143 species following the discovery of new species (Traiperm et al. 2019;Traiperm and Suddee 2020) and the establishment of new combinations (Shalini et al. 2017;Staples and Traiperm 2017;Rattanakrajang et al. 2022). There are about 25 species in China (14 of which are endemic) and 92% of the species found in China in Yunnan Province (23 recorded species). The province of Yunnan is, therefore, the main center of diversity in China (Fang and Huang 1979;Fang and Staples 1995;Yang et al. 2015).
Loureiro (1790) published Argyreia as a genus within Convolvulaceae. The genus is mainly characterized by indehiscent fleshy or mealy berries (Staples and Traiperm 2017). The various types of indumentum, inflorescence architecture, depth of corolla lobes, and number of seeds in individual berries are the main taxonomically informative characters for the delimitation of species in Argyreia.
Argyreia seems to be non-monophyletic in recent works, because it includes at least one of the moth-pollinated species of Rivea Choisy (Manos et al. 2001;Stefanovic et al. 2003). Furthermore, there is evidence that Blinkworthia Choisy should be subsumed under Argyreia (Rattanakrajang et al. 2022). We support this conclusion and although the Argyreia alliance clade as recovered is paraphyletic, only one Rivea species was used and the inclusion of other species might lead to different conclusions in the future (Rattanakrajang et al. 2022). Therefore, we think that Rivea and Argyreia are two independent genera and both supposedly monophyletic, but their limits should be revised under a phylogenetic perspective with a comprehensive sampling.
Although recent studies have shown that Argyreia should be treated as part of Ipomoea L. (Muñoz-Rodríguez et al. 2019) and Argyreia is merged into Ipomoea by Wood et al. (2020), we chose not to follow the proposed classification in the present work, as further study of Old World taxa is still required (Traiperm and Suddee 2020). As it concerns Ipomoea, the possibility to keep the several established smaller genera has the potential to maintain nomenclatural stability (Eserman et al. 2020). So we do not subsume Argyreia into Ipomoea at this time and accordingly maintain the well-established generic concepts (Rattanakrajang et al. 2022).
During recent field surveys in Yunnan Province, an interesting population of Argyreia with an entire or shallowly lobed corolla was found. After reviewing literature and comparing specimens, especially native species in Yunnan Province and adjacent countries (Vietnam, Laos, Myanmar, Cambodia and Thailand), we found that the taxon was not completely similar to any species known worldwide. Therefore, a new Argyreia species from China is described and illustrated here.

Material and method
Plant material was collected during field surveys in Yunnan Province from 2020 to 2021. The type specimens have been stored in the herbarium of Beijing Normal University (BNU). Morphological measurements were made from dried specimens of herbarium by Nikon digital camera, Stereoscope (ZEISS V8) and software ImageJ (Abràmoff et al. 2004). Materials for observation of pollen morphology were obtained from herbarium, picking mature pollen from the dried specimens, sticking it on the sample stages with conductive adhesive, spraying gold and photographing by Scanning Electron Microscope. The collected specimens were compared with the type specimens of morphologically similar species at main herbariums in China (BNU, HITBC, IBSC, KUN, PE, WUK, YUKU), as well as digital images available online provided by JSTOR and herbaria abroad that are relevant for the group (A, BM, E, G, K, P). Fresh plant materials of the similar species (A. wallichii) were also collected for further careful comparison. All type specimens (or photos of type specimens) of accepted names and their synonyms in Argyreia known around the world were examined, which refer to the voucher information provided by Staples and Traiperm (2017).

Diagnosis.
A. subrotunda is unique, a small-flowered type with an entire or shallowly lobed corolla as well as exserted stamens and pistils (included in dry specimens), smaller elliptic bracts, and outer sepals ovate-circular. It is similar to A. wallichii in indumentum features (whitish tomentose) and fruit types (red globose berry), but differs by its smaller elliptic bracts (vs. ovate-oblong), lax flat-topped cymes (vs. compact capitate) and shorter corolla tubes (2-2.5 cm vs. 4-5 cm). Additionally, A. subrotunda is similar to A. fulvocymosa in leaf shape (broadly ovate-circular to nearly circular) and inflorescence (flat-topped cymes), but the latter is covered with densely yellowish villus and has a distinctly 5-lobed corolla, which is very easy to distinguish (Table 1).
Phenology. Flowering from August to November; fruiting in November to February. Distribution and habitat. Distributed in Yunnan and Gaungxi Province (Fig. 3), occurring at elevations of ca. 650-1300 m, distributed at open and sunny places such as roadsides, thickets, edges of mingled forest.
Preliminary conservation status. Least Concern (LC). At present, five populations have been collected in Malipo County, Maguan County and Napo County. Each population is large with high flowering rates, and the number of mature individuals in the population is more than 50. According to the IUCN (2019) red list categories and criteria, A. subrotunda should be categorized as a 'Least Concern (LC)' species, which needs further investigation and research to more fully assess the conservation status.
Etymology. The specific epithet refers to the leaf shape, which is near-round.

Pollen morphology
The observed pollen grains of A. subrotunda were monad, spheroidal to subspheroidal and radially symmetrical, with polypantoporate and echinate ornamentation (Fig. 4). It was possible to divide into two types based on the pollen morphology as follows: the diameter of the pollen grain was less than 100 μm with shorter bottle-like spines (5-7 μm), such as A. wallichii and the new species A. subrotunda; the diameter of pollen grains was over 100 μm with longer cone-shaped spines (≥ 10 μm), such as A. marlipoensis, which is endemic to Yunnan province, and the flower of which is first seen in this study.

Discussion
Morphologically, this species is most similar to A. wallichii and A. fulvocymosa, and it can be easily distinguished by the characters summarized in Table 1. The new species was similar to A. wallichii, both having similar indumentum features and fruit types as well as being almost sympatric. However, based on 17 specimens from two populations of A. subrotunda, we found the length of corolla was a very stable feature, about 2-2.5 cm, which was significantly shorter than A. wallichii (4-5 cm). The latter could also be easily distinguished from the new species by its compact capitate cymes and ovate-oblong bracts instead of flat-topped cymes and elliptic bracts. Additionally, A. subrotunda was similar to A. fulvocymosa in leaf shape and inflorescence, but the latter had a distinctly 5-lobed corolla instead of an entire or shallowly lobed corolla. Morphological comparisons of fresh plants between A. subrotunda and A. wallichii were provided in Figure 5. Furthermore, detailed comparisons of A. fulvocymosa, A. subrotunda and A. wallichii were provided in Table 1.  The discovery of the new species has important value for further understanding of the morphological patterns of Argyreia in China. The new species is endemic to southwest China and compared to other species with an entire or shallowly lobed corolla in China, it seems to have comparative smaller corollas, which reinforces its recognition as a new taxa.
Key to the species of Argyreia from Yunnan, China