This a beautiful example of a simple ternary form.
Part A, (mm. 1-13), a phrase group in Ab major, represents a tonally closed expository section ending on a PAC. There may be argument for a Half Cadence at the end of measure 5, but I don't really hear one. Schumann uses varied rhythms and articulations to correllate with the lyrics. The busy accompaniment moves under a soaring soprano line. It is a beautiful exposition, with the high point of the section coming on the seventh of a secondary dominant chord. The section ends ritarding and decrescendoing gracefully into a PAC.
The changes in tonality, accompaniment style, and motivic content provide the contrast necessary for part B. In the foreign key of E major, we encounter another phrase group. The first two phrases are nearly identical, ending on HC, with the second phrase embellishing the B theme. The final phrase is clearly developmental and transitional, ending 4 bars later, leaving this section tonally open. Important phenomena include dynamic changes, embellishments, modulation, and a rhythmically slow contrasting theme.
After the middle section, we transition back to the A section and Ab major, signalled by a ritardando. The recapitulation is varied, starting and ending different from the beginning. Again I think I would consider this to be a phrase group, however, there are a few more PACs making this concluding section a bit more organized. The piece ends on a PAC, followed by a cadential extension in the piano.