Comments on Unified dark energy and dark matter from a scalar field different from quintessence

In a recent paper by C. Gao, M. Kunz, A. Liddle and D. Parkinson [arXiv:0912.0949], the unification of dark matter and dark energy was explored within a theory containing a scalar field of non-Lagrangian type. This scalar field, different from the classic quintessence, can be obtained from the scalar field representation of an interacting two-fluid mixture described in the paper by L.P. Chimento and M. Forte [arXiv:0706.4142]