Larsa Pippen and Marcus Jordan appear to have scrapped their friendship for a full-blown romance -- the two were closer than ever during a day at the beach this weekend.

Scottie Pippen's ex-wife and Michael Jordan's 31-year-old son enjoyed the sun in South Beach on Sunday ... with Larsa sporting a tiny, black bikini and Marcus going with a black backwards Jordan Brand hat and patterned trunks.

48-year-old Larsa has previously insisted she's just friends with MJ ... but they sure looked like a couple as he wrapped his arm around her during the beach day.

The two also got really cuddly while getting some shade under an umbrella ... with witnesses saying they were making out at one point.

If they're really just buddies, they certainly don't mind showing affection for each other in public -- as TMZ Sports previously reported, Larsa was spotted kissing MJ's neck at Rolling Loud in NYC back in September.

The two were first spotted together in Miami earlier that month ... in what appeared to be a double date at a Japanese restaurant. We were told at the time they were just friends who were hanging out with people in their same social circle ... although things certainly appear to have gotten more serious since then.

Larsa was married to Scottie for 23 years ... and they have four kids together.