Definition of black root
1
: any of several plants or their dark-colored roots: such as
a
: a perennial plant (Pterocaulon undulatus) of the southern U.S. that has large black rootstocks
b
: culver's root
c
: colicroot 1
d
: a common comfrey (Symphytum officinale) with the upper part of the stem and inflorescence densely hispid
2
: any of several plant diseases characterized by dark discoloration of roots: such as
a
: cotton wilt 1
b
: a disease of radishes, beets, and sugar beets caused by fungi (genus Aphanomyces) and producing brown or black lesions on the roots, deformation of the roots, and a damping off of seedlings
