Riemann sum with pgfplots -- can't seem to make graph look right

You can fix this problem by using the ybar interval style for both plots, but reversing the direction for the lower sum by using domain=17:1 instead of domain=1:17:

\documentclass[border=5mm]{standalone}

\usepackage{pgfplots}

\pgfplotsset{compat=1.9}

\begin{document}
\begin{tikzpicture}
\begin{axis}[
    xtick={0,1,3,5,7,9,11,13,15,17},ytick={0,...,1.5},
    xmax=18,ymax=1.2,ymin=0,xmin=0,
    enlargelimits=true,
    axis lines=middle,
    clip=false,
    domain=0:17,
    axis on top
    ]

\addplot [draw=red, fill=red!10, ybar interval, samples=9, domain=1:17]
    {x^-1}\closedcycle;
\addplot [draw=green, fill=green!10, ybar interval, samples=9, domain=17:1]
    {x^-1}\closedcycle;

\addplot[smooth, thick,domain=1:17,samples=40]{x^-1};

\end{axis}
\end{tikzpicture}
\end{document}