Abstract: Seed micromorphological characters of 29 species of Hydrangea were studied under SEM （Scanning Electron Microscope）. Two types of seeds，viz. ellipsoid and oblong were observed with reticulate and reticulate polygon ornamentation patterns. The ridges of reticulation varies from undulate，sinuate or substraight and some rugae and without ornamentation. Shape and ornamentation patterns are specific to sections and these results also support in traditional taxonomy. Section Petalanthae were character of ellipsoid seed，undulate or sinuate ridges，irregular or regular foveate cavities among ridges；sect. Hydrangea were with ellipsoid seeds，substraight ridges，no ornamentation among ridges；sect. Cornidia and sect. Heteromallae were characterized by oblong seeds，substraight ridges，smooth among ridges；sect. Calyptranthe were of oblong or ellipsoid seeds covered with reticulated polygon ornamentations，some small foveate cavities in polygon lumina. The results indicated that seeds micromorphological characters of Hydrangea showed high specificity in sectional level classification. In addition，it has high value in circumscription among infrasectional relative species as well as with systematic significance in phylogenetic reconstructions.

Key words: Hydrangea, seed, micromorphology, systematics, SEM