Dewberry \Dew"ber`ry\, n. (Bot.)
   (a) The fruit of certain species of bramble (Rubus); in England, the fruit of Rubus c[ae]sius, which has a glaucous bloom; in America, that of Rubus canadensis and Rubus hispidus, species of low blackberries.
   (b) The plant which bears the fruit. [1913 Webster]

Feed him with apricots and dewberries. --Shak. [1913 Webster]

Source: The Collaborative International Dictionary of English v.0.48
 

Blackberry \Black"ber*ry\ (bl[a^]k"b[e^]r*r[y^]), n. [OE. blakberye, AS. bl[ae]cberie; bl[ae]c black + berie berry.]

The fruit of several species of bramble (Rubus); also, the plant itself. Rubus fruticosus is the blackberry of England; Rubus villosus and Rubus Canadensis are the high blackberry and low blackberry of the United States. There are also other kinds. [1913 Webster]

Source: The Collaborative International Dictionary of English v.0.48
 

Rubus canadensis

Source: WordNet (r) 2.0