"R-Genex", short for "Real Genex" (レアル・ジェネクス, Rearu Jenekusu) in the OCG, is a sub-archetype of the "Genex" archetype, serving as support cards. Their effects are based on Special Summoning more "R-Genex" and "Genex" monsters onto the field, thus allowing any "Genex" Deck to swarm and Synchro Summon quickly. As "Genex" cards, they receive implicit support from that archetype's support cards.
Running a completely pure "R-Genex" Deck is close to impossible, due to very little support, a lack of any powerful monsters and effects that support the "Genex" archetype more than themselves. A few "R-Genex" monsters are a welcome addition in "Genex" Decks, helping to increase the speed of the Deck and adding much-needed swarm power. The prime example is "R-Genex Accelerator", which allows you to Special Summon a "Genex" monster added from the Deck to the hand. Many draw/search cards can make a reasonably fast swarm for a relatively easy Synchro Summon.