The concept of the rhizome as a representation of the structure of knowledge was first proposed by Gilles Deleuze and Felix Guattari in A Thousand Plateaus - wikipedia 
The rhizome is stem of plant, like hops, ginger or japanese bamboo, that helps the plant spread and reproduce. It responds and grows according to its environment, not straight upwards like a tree, but in a haphazard networked fashion.
The six principles of a Rhizome by Deleuze & Guattari are:
- Connection
- Heterogeneity
- Multiplicity
- Asignifying rupture
- Cartography
- Decalcomania
The ideas described in the book were disruptive at the time of publication, but recently have become post-hoc explanations for several contemporary knowledge phenomenon such as social media.
Rhizomatic philosophy attempts to explain knowledge using the comparison of a rhizome and a tree. While the tree is ruled by hierarchy, linearity and a meaningful pattern; the rhizome is an unbounded, distributed, semiotic and interconnected scaffold - royalcollege.ca