Hi there, I am one of those professional plant people, and I deal with dracaenas a lot. I had a long chat with the wholesale greenhouse lady where I buy my plants about dracaena marginatas recently. She told me that when they are grown in Florida, they grow them under very high light with lots of fertilizer, so that they grow fast. Time is money, the faster they get the plant to full size, the sooner they can sell it and use the space to grow another one. With all of this light and water, their leaves are very firm, to the point that they can give you an extremely painful poke in the eye, like being poked with a stick (don't ask me how I know this...) A plant will keep these stiff leaves for several months after being put into its office location. If the light is very bright, the leaves will stay stiff. If the light is dim, they will gradually start to droop over time. Once they droop, I don't think they can get stiff again, at least not those particular leaves. The droopy plants that you see the plant company caring for probably only need water every two to four weeks, especially if it is dark and/or cold. I do not recommend moving marginatas into cold. They do not like cold at all, and it will lead to the lower leaves turning a mushy yellow, along with all sort of possibilities for root and stem rot. Marginatas do like to be kept dry, especially if they are in a dim location. Not as dry as a cactus, but pretty darn dry. When in doubt, err on the side of not watering. The ones you see the plant company take care of with the stiff leaves? It is quite possible that they remove them and replace them with new ones periodically, and that is why the leaves appear to stay stiff. Hope that helped!

This is the first picture from that post. It looks sort of Carissa macrocarpa-esque: there are several strange cultivars with which I'm not familiar. Does it have any thorns? Milky sap if a leaf is broken?

Pulled these off my Carding Mill today: Here’s the plant, with the affected leaves pulled off: Thanks!

it turned up now.. because its that time of year .. imo... its probably extremely humid nights and mornings... that are conducive to mold..mildew.. and fungus growth... drought does not help.. but then its usually less humid if you go into extended deep drought.. but when the drought breaks.. they will come... you are hitting all the variables but not recognizing them... good work.. it will all come.. ken ps: as fall rolls in.. the dewey nights.. will show you all the spider webs all over the yard.. another free show of ma nature.. please dont go out there.. and broom them all out of the plants.. spiders are our friend.. outdoors anyway.. lol... thing is.. by fall .... they have all matured.. so the webs are large... so easy to notice... fall is also a good time for the late fall shroom season.... personally.. id ont eat any of those .. too many can be problematic... but thats a different show...