Amongst the symbols adorning the lotus feet of the Divine Couple, the flower symbol is unique to Sri Radha.
The flower indicates that Her feet are especially soft and delicate. Moreover, the flower-like fragrance emanating from Her lotus feet attracts and invites devotees who, just like honey bees, come and gather the pollen of Her madhurya prema (affection of a lover) which they then distribute to other fortunate souls.
The absence of the flower symbol on the feet of Sri Krishna invites His servants to offer Him some petals of our own.
Krishna extends this invitation not due to any lack or need on His part. Rather, this invitation is a consequence of His yearning for us to offer Him our hearts, which are symbolized by the flower. Because Krishna's own heart has been stolen by the innocent charm of His beloved Radha, the offering of a flower by His devotee is more precious to Him than all of creation.
Yet it is Radha alone Who possesses the beauty to attract the all-attractive Krishna. She is the internal, primeval potency of the Lord; the personification of His hladini sakti (pleasure potency).
Srimati Radharani is also the transformation of Krishna's love. As such, She is the manifestation of His mercy; and most significantly, it is only through Her grace that devotees attain the Lord in His Supreme Abode.