The Collaborative International Dictionary of English v.0.48:

Undissembling \Undissembling\
   See dissembling.

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "undissembling":
   arcadian, bucolic, candid, genuine, guileless, homespun,
   inartificial, native, natural, naturelike, open, openhearted,
   pastoral, plain, rural, straightforward, unadorned, unaffected,
   unartificial, unassumed, unassuming, unbeguileful, unbeguiling,
   uncalculating, unconcealed, undeceitful, undeceiving, undeceptive,
   undesigning, undisguised, undisguising, undissembled,
   undissimulated, undissimulating, unembellished, unfeigned,
   unfeigning, unflattering, unpretended, unpretending, unpretentious,
   unspoiled, untrimmed, unvarnished