The growth of hypogeal stem contain tri-growth, and the anomalous secondary growth is the result of supernumerary cambium that derived from the outmost elements of secondary phloem.

• 地下茎加粗过程中形成三生结构，其异常结构是由于次生韧皮部外侧发生的额外形成层所致，其起源于薄壁细胞；