Trivalvaria is a genus of plant in the custard apple family (Annonaceae). The small trees and shrubs inhabit tropical lowland rainforests of Tropical Asia including Hainan. To date, there is only one Trivalvaria species recorded in China. 

In their field survey in southeast Yunnan, researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences and their collaborators found a species possessing leaves with eucamptodromous venation and scalariform tertiary veins, extra-axillary inflorescence with short pedicels and cream-colored flowers, and hence recognized as a member of the genus Trivalvaria. 

After careful morphological and molecular phylogenetic studies, the researchers confirmed that the plant represents a new species. They named it as Trivalvaria tomentosa to refer to the tomentose indumentum on the twigs, leaves and flowers and got it published in Nordic Journal of Botany. 

Trivalvaria tomentosa is a shrub to two meters tall. It has tomentose twigs, petioles, abaxial surface of the leaves, sepals and petals. It is similar to T. stenopetala in leaf size and shape, but differing in having tomentose or pubescent indumentum on old twigs, leaves and monocarps, as well as lanceolate and recurved petals. 

Trivalvaria tomentosa is phylogenetically close to T. macrophylla. However, T. macrophylla is easily differentiated from T. tomentosa by having connivent inner petals at anthesis. 

The new species is distributed in southeast Yunnan (Hekou, Jinping, Maguan, Pingbian) at 250–900 m elevation. It mainly grows in tropical evergreen forest. It comes to flowering in April to May and fruits from May to December.