What is the main difference between Hemp and Kenaf?

They’re two entirely different plants, very distantly related. They share the same class–magnoliopsida, but not the same order, family, genus, or species.

Kenaf complete taxonomy: Plantae Magniliophyta magnoliopsida Malvales Malvaceae Hibiscus cannabinus)

. a tropical plant, Hibiscus cannabinus, of the mallow family, yielding a fiber resembling jute.

. the fiber itself, used for cordage and textiles.

http://dictionary.reference.com/browse/kenaf

Hemp complete taxonomy: Plantae Magnoliophyta Magnoliopsida Rosales Cannabaceae Cannabis sativa

. Also called Indian hemp, marijuana. a tall, coarse plant, Cannabis sativa, that is native to Asia but naturalized or cultivated in many parts of the world and is the source of a valuable fiber as well as drugs such as marijuana and hashish. Compare cannabis.

. the tough fiber of this plant, used for making rope, coarse fabric, etc.

. any of various plants resembling hemp.

. any of various fibers similar to hemp.

. a narcotic drug, as marijuana or hashish, prepared from the hemp plant.

http://dictionary.reference.com/browse/hemp