Sargassum primitivum sp. nov. is mainly characterized by its receptacles cylindrical with a few spinules or teeth limited to the apices. The new species is regarded as a primitive member of the Swartzia group. It is related to S. swartzii on the one hand and to S. virgatum of Fruticuliferae on the other, differing from the former in its cylindrical receptacles and leaves with some sharp teeth and from the latter in its toothed receptacles and broader toothed leaves.

Sargassum hainanense sp. nov. is closely related to S. dumosum, differing in the elongated linear leaves, and the vesicles with leaf-like stalk without teeth at the margin.

Sargassum wenchangense sp. nov. is cartilaginous to very firm (unusual for Sargassum), and short. It is related to S. Hainanense differing in its very short upper leaves, half of the upper leaves of S. hainanese, vesicular pedicels cylindrical and the receptacles dilated in the upper parts, fan-like.

Sargassum pusillum sp. nov. is related to S. swartzii differing in the frond very small, to about 11 cm high, leaves on the secondary branches very asymmetrical, oblanceolate, broad linear or linear, with irregular serrate margins, pedicels flate, with a few serrate margins, receptacles usually dilate above and conspicuous spinules at the apices and margins. These characteristics make it easy to differentiate from other closelyirelated species such as S. swartzii.