Abstract: On the sandy ground of Min-qin county, under the condition of different localities, there are plants of different types of tillering characteristics. Plants on the fixed and semi-fixed sand dunes are of tap root type, those of the lowland among the dunes belong to the rhizome type; while the root shooting represents a transitional type between the above two types. Sand covering and its changes are important factors affecting the tillering characteristics of plants. As the sand cover thickens, plants adapt themselves by elongating their root crowns and developing two or more root crowns, two layers of horizontal roots or rhizomes. Judging from the characteristics of tillering, Iris ensata may be considered as an aberation of a biennial, or a pseudo-perenial. Basing on these facts, the authors suggest a few principles of classification of the life span of plants in close connection with the time of existence of the terrestrial and subterraneous parts of the plants.