﻿A new species of Sterculia (Malvaceae) from Vietnam

﻿Abstract A new species of Sterculia from Vietnam – S.konchurangensis – is described, illustrated, and compared with the similar S.lanceolata. S.konchurangensis differs from S.lanceolata by the length of the petiole (7.0–9.5 vs. 25–35 mm), shape of the leaf blade (obovate or elliptic vs. elliptic, lanceolate or elliptic-lanceolate), length of the leaf blade (6–8 vs. 9–20 cm), and length of the calyx lobe (11–12.5 vs. 4–6 mm). A diagnostic key of the 22 Sterculia species occurring in Vietnam is also provided.

During a botanical survey of the Gia Lai province (the Central Highlands of Vietnam) in 2022, plants referred to the genus Sterculia were observed in a primary evergreen forest in the Kon Chu Rang Nature Reserve. After comparing the collected specimens with others preserved in various herbaria, and by consulting relevant literature, we reached the conclusion that Vietnamese population represent a new species for science which is here described and illustrated. We also provide a key to the species of Sterculia that are now known to occur in Vietnam. Diagnosis. Sterculia konchurangensis is most similar to S. lanceolata Cav. due to the number of veins on each side of midrib, length of inflorescence, deeply divided calyx, globose, hairy ovary and curved style. They are separated by morphology of leaf blades (obovate or elliptic in S. konchurangensis vs. elliptic, lanceolate or elliptic-lanceolate in S. lanceolata); petioles are shorter (7.0-9.5 mm vs. 25-35 mm in S. lanceolata), leaf blades are shorter (6-8 cm vs. 9-20 cm in S. lanceolata) and calyx lobes are longer (11-12.5 mm vs. 4-6 mm in S. lanceolata).
Etymology. The specific epithet refers to the type locality, Kon Chu Rang reserve in Vietnam.
Distribution and ecology. Sterculia konchurangensis is only found in Vietnam, Gia Lai province, Tay Nguyen area, Kon Chu Rang reserve where it grows in primary evergreen forest at an altitude of 1016 m a.s.l. Flowering time is June; fruiting time is unknown.
Conservation status. Data Deficient (DD; IUCN 2019). Sterculia konchurangensis is known only from the type locality within Kon Chu Rang reserve. A comprehensive botanical survey of the Sterculia has not been carried out to date.
Discussion. Sterculia konchurangensis is morphologically similar to S. lanceolata Cav. due to the number of veins on each side of midrib, length  of the inflorescence, deeply divided calyx, globose, hairy ovary, and curved style; furthermore, to be noted that both species have the same flowering time (June). However, S. konchurangensis differs from S. lanceolata by the morphology of length of petiole, shape of leaf blade, size of leaf blade and length of calyx lobe.
The identified key of 23 species of Sterculia in Vietnam was constructed. Sterculia konchurangensis differs from 22 species of Sterculia by having some characters such as simple, entire, glabrous leaves and length of petiole (less than 12 mm long). In addition, the comparison with the similar species (S. lanceolata) confirms that S. konchurangensis is a new species. Diagnostic characters separating the two species are listed in Table 1.  Seeds 2