The Collaborative International Dictionary of English v.0.48:

Acaulescent \Ac`au*les"cent\, a. [Pref. a- not + caulescent.]
   (Bot.)
   Having no stem or caulis, or only a very short one concealed
   in the ground. --Gray.
   [1913 Webster]

WordNet (r) 3.0 (2006):

acaulescent
    adj 1: (of plants) having no apparent stem above ground [syn:
           acaulescent, stemless] [ant: caulescent, cauline,
           stemmed]