  Most parameterizations of the dark energy equation of state do not reflect
realistic underlying physical models. Here, we develop a relatively simple
description of dark energy based on the dynamics of a scalar field which is
exact in the limit that the equation of state approaches a cosmological
constant, assuming some degree of smoothness of the potential. By introducing
just two parameters defined in the configuration space of the field we are able
to reproduce a wide class of quintessence models. We examine the observational
constraints on these models as compared to linear evolution models, and show
how priors in the field space translate into priors on observational
parameters.
