This was a definite made-for-tv, low-budget movie I saw on the Sci-Fi Channel a few years ago.
A demolition crew is in the process of tearing up an old military base when they come across a hidden room. In the middle of the room there is a tomb-like vault. When they remove the top of the vault they find it full of water and a drowned test monkey (or maybe a person) with a strange plant growth coming out of it’s chest. They take photos and the light from the camera flash starts the plant growing at a fast pace, killing everyone it touches. The survivors reason that if the plant is growing this fast at night, then it will be unstoppable once the sun rises. One person realizes that the plant is actively avoiding him and it turns out that this guy’s blood acts like Roundup to the plant so he has to find his way back to the vault and kill it at the source.