The paper reports a new record genus of Boraginaceae,Microcaryum,and a new record species,Microcaryum pygmaeum (Clarke)Johnst.,in Xizang.M.pygmaeum growing in the altitude of 5 000 m,was found in the alpine meadow of Longzi Xizang.The characteristics of its external morphology,nutlet and pollen epidermal micromorphology were studied in detail,and the differences between it and the related species Lasiocaryum densiflorum (Duthie)Johnst.were presented in the paper.The voucher specimen is deposited in the herbarium of Beijing Normal University(BNU).