From the experts:
Acacia is an attractive, rarely used Greek flower name enhanced by its popular beginning-and-ending-with 'a'-construct, and is gradually beginning to catch on with baby namers.
The acacia is a shrub of the mimosa family, with clusters of showy white or yellow blossoms, which symbolizes resurrection and immortality--making the name especially appropriate for an Easter-season baby.
Named by an early Greek botanist, the acacia is known for its fine wood and medicinal properties. It also has biblical ties, since the Ark of the Covenant was made out of Acacia wood.
As a given name, Acacia has had some popularity in Australia, where the acacia (sometimes known there as the wattle) is a common plant and sometime national symbol.