Two are herbaceous (they die back to the ground each winter):
Aralia nudicaulis, Wild Sarsaparilla
Up to 18" tall; the inconspicuous flowers are below the leaves.
Aralia racemosa, American Spikenard
Up to 6' tall and wide, with flowers in a showy panicle.
Uncommon in the Piedmont; rare on the coastal plain.
Two are shrubs or small trees, covered with prickles.
They are very similar and can be hard to distinguish, but in Delaware A. spinosa is found only on the coastal plain,
and A. elata is found only in the Piedmont (so far.)
For details on the differences between these two species see
this booklet from the Delaware Department of Agriculture.
Aralia spinosa, Hercules Club
Coastal plain only.
Aralia elata, Japanese Angelica-tree
Piedmont only; invasive alien.
This is a relatively new plant in our area, sometimes misidentified as A. spinosa.
Sources: The Flora of Delaware, Herbaceous Plants of Maryland.