The Collaborative International Dictionary of English v.0.48:

Dextrorsal \Dex*tror"sal\, Dextrorse \Dex"trorse`\, a. [L.
   dextrorsum, contr. fr. dextrovorsum, dextroversum, toward the
   right side; dexter right + versus, vorsus, p. p. of vertere,
   vortere, to turn.] (Botany)
   Turning from the left to the right, in the ascending line, as
   in the spiral inclination of the stem of the common
   morning-glory; as, dextrorse vines.
   [1913 Webster]

   Note: At present scientists predicate dextrorse or
         sinistrorse quality of the plant regarded objectively;
         formerly the plant was regarded subjectively, and what
         is now called dextrorse was then considered
         sinistrorse.
         [1913 Webster]

WordNet (r) 3.0 (2006):

dextrorse
    adj 1: spiraling upward from left to right; "dextrorse vines"
           [syn: dextrorse, dextrorsal]