Diadelphous stamens are found in :

Diadelphous stamens are a type of floral arrangement in which the stamens are united into two groups: usually nine stamens are fused together into a single bundle, while the remaining tenth stamen is free.

This characteristic is a hallmark of many plants in the Fabaceae (legume) family. The classic example of a plant that exhibits diadelphous stamens is the pea (Pisum sativum), where the flower’s stamens are organized exactly in this 9‑plus‑1 pattern.

Other listed options, such as the China rose (Rosa chinensis) and citrus (Citrus spp.), do not display this staminal configuration; their stamens are typically free or only minimally fused, not forming the distinctive diadelphous bundle.

Therefore, based on botanical morphology, the correct answer to “Diadelphous stamens are found in:” is Pea.