Can I bring a large metal rose on a plane?

Depends. You're probably OK, since metal flowers don't match any of the TSA prohibited items list, and even though the leaves and rose tips may be sharp, I presume any "blades" are less than 4 inches long. The "sharp items" list is intended to cover stabbing weapons that could cause serious damage, and I presume a metal rose would not really fit the bill.

However, there's a non-zero chance that you'll run into an inspector who disagrees and confiscates it anyway, because sharp = bad in his book. Are you willing to run this risk? Would checking it in as luggage be an option?

(Note: I'm assuming this is the USA here, which generally has the craziest carry-on limits. The same applies anywhere though, only with a decreasing likelihood of confiscation.)

No, according to the sharp objects guidelines. Additionally, I've had a kid's 18-inch baseball bat confiscated. I had to leave it with the security officers and enter the plane. And of course, there were no sharp edges but it was heavy and dangerous.

You don't specify country, route or airline, which makes it harder to answer with any certainty.

When travelling internationally and within an Asian country I have personally had utterly harmless items confiscated by security staff and have heard numerous accounts of relatively innocuous items being confiscated. These include finger-nail clippers (not small scissors) - which is ludicrous but shows what may happen. I had an inkjet refilling device confiscated on an internal Chinese flight after it had previously been carried without problem on several international hops and one internal flight. It contained 3 very short needles internally (used to puncture an inkjet cartridge). A good set of fingernails and/or teeth would have been more dangerous. (I was carrying it in carry-on to minimise the risk of pressure variations causing ink leakage - probably not a problem in modern cargo holds). (As an example of how little thought through or truly useful such policies are - an airline tray table would be easily enough liberated and would make quite a useful weapon - and every aircraft supplies one for every passenger.)

Overall, I'm amazed at the advice that the rose may be OK.
It may be correct advice (or not) but I'm still amazed.
"When a man with a boxcutter meets a man wit a 14" all metal somewhat heavy rose, who wins?" I'd have thought that the rose would make a far more formidable weapon than the weapons used on the original 911 flights. And, if an 18" baseball bat is explicitly prohibited then why would a 14" all metal rose be considered safe?

I'd consider a TSA man (or woman) not to be doing their job properly if the bat was confiscated and the rose wasn't. Your (air) milage may vary, but I certainly would not risk it.