Researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) and the Institute of Botany of the Chinese Academy of Sciences have identified a new genus and species of flowering plant in the dry-hot valleys of the Red River basin in southwest China's Yunnan Province. Morphological and molecular phylogenetic analyses confirmed that the plant constitutes a new genus within the Marsdenieae tribe of the Apocynaceae family.

They named the new genus Xua and its species Xua hongheensis in honor of Prof. XU Zaifu, former director of XTBG, in recognition of his long-term dedication to and contributions to the conservation and utilization of tropical plants in China.

The findings were published in Journal of Systematics and Evolution on Sept. 15.

Xua hongheensis is a perennial, twining herb that can grow up to three meters long. Its slender stems are densely hairy, while its opposite leaves are elliptic to broadly ovate. One of the species' most distinctive features is its fleshy, erect staminal corona lobes, which have concave apices. The plant also produces four-angled, spindle-shaped follicles measuring seven to eleven centimeters long, along with flat, winged seeds bearing a white coma.

Morphological comparisons show that Xua differs from its closest relatives. It resembles Sarcolobus in having a very short corolla tube and spreading lobes, but can be distinguished by its solid shoots, peduncles 5–12 mm long, and tetragonal-fusiform follicles. Compared with six other allied genera, Xua has an almost tube-less, rotate corolla and unique erect corona lobes with concave tips.

Field surveys showed that Xua hongheensis is only sporadically distributed in dry-hot valley habitats at elevations of 350–1,200 m in the Red River basin, Yunnan. It grows in forest gaps of tropical seasonal rainforests and in the understory of savanna shrub-grasslands. The researchers preliminarily assessed the conservation status of the new genus as Data Deficient (DD) under the IUCN Red List Categories and Criteria.

"Our study adds a new genus to Apocynaceae. More field surveys are needed to discover the endemic plant diversity of the unique and under-explored biodiversity of the dry-hot valleys of the Red River in Southwest China," said SHEN Jianyong of XTBG.

Xua hongheensis (Image by SHEN Jianyong)

Xua hongheensis (Image by SHEN Jianyong)

Xua hongheensis (Image by SHEN Jianyong)

Xua hongheensis (Image by SHEN Jianyong)