Possession marijuana in the State of Florida can be charged in a couple of different ways. There is a charge for possession of marijuana under 20 grams, which is a very small amount. This is a first offense punishable by 1 year jail and a $1000 dollar fine. Above that, it becomes a 3rd degree felony which is punishable by 5 years prison and a $5000 dollar fine. If there is allegation that you're selling marijuana, that becomes a felony regardless of the amount that you are selling.
If all you have is stems or shake, which is essentially unsmokable marijuana, are you really looking at the possibility of being charged with possession? The answer is yes - there is no distinction in the law in regards to what part of the cannabis plant you need to be in possession of for them to charge you. Unfortunately, a lot of times people have stuff that's not even usable, and realistically is not a consumable drug. They will find themselves charged nevertheless.
The other thing you should keep in mind in regards to marijuana: You can find yourself with an additional charge because of possession of paraphernalia. Paraphernalia includes typically what you are probably thinking about, such as needles and spoons for doing crack ccocaine or methamphetamine, or pipes for smoking marijuana, but it also runs the gambit with regards stuff that you wouldn't typically think of as paraphernalia, such as vizine which people can use to get the red out of their eyes from smoking pot. It also includes baggies, rolling papers, Dutch Masters, etc..
When it all stands alone, it's completely legal of course. If the cops can prove that you intended to use it in conjunction with drug possession, (i.e. you obviously if you have rolling papers right next to a bag of pot), or you have a marijuana cigarette, they will most likely charge you not only with the possession of marijuana, but with possession of drug paraphernalia as well. Interestingly enough, that's good and bad. This is because often a good attorney can get the state attorney in situation like that to drop the possession charge, and perhaps just plead you out with the possession of the paraphernalia charge. And what that will do is hopefully avoid the conviction for you, if you get a withhold of adjudication with that but it will certainly avoid the necessity of a 2 year driver's license suspension.