It's not likely stacci botrus, it certainly appears to be a black mold.
You can have it tested. Someone is very likely allergic to it. Get rid of it.
Stacci is usually found on paper, newsprint and magazines.
Agreed. This section of gypsum was removed, and replaced with new. We didn't test it. It is common here when supply discharge leaks in areas with surrounding dew points in the 70's. That job was done earlier this year, and they were happy campers this summer with a new 16 SEER 2 speed system along with a leakage correction.
Boy, for a product that is "resistant to mold" (fiberduct), that sure is a lot of mold...lol.
Now that is news to me. It is a mold sponge, if the A/C is abused. I've got some shots of duct board insides that will make you lose your appetite.
It is important to eliminate the variables that allow this to happen. We have removed 15 year old systems, that with proper original install, dialed-in airflow, sealed duct system, and scheduled maintenance, the duct board looked pristine brand-new.