  We report the first observation of the decay D^+ -> eta' e^+ nu_e in two
analyses, which combined provide a branching fraction of B(D+ -> eta' e nu) =
(2.16 +/- 0.53 +/- 0.07) x 10^{-4}. We also provide an improved measurement of
B(D+ -> eta e nu) = (11.4 +/- 0.9 +/- 0.4) x 10^{-4}, provide the first form
factor measurement, and set the improved upper limit B(D+ -> phi e nu) < 0.9 x
10^{-4} (90% C.L.).
