Hi again!.....this is a problem that i just noticed with a new dendrobium that i just got. The plant is extremely healthy, but today i notcied that on about 2-3 leaves (there are 12 leaves in total) there are some dots. Black dots on the surface of the leaf, as well as on the inside part on the base of the leaf where it attaches to the plant. On the back of the leaf (underside) it looks like dried dirt, but i cannot scrape it off. This pic is not the best.. and i'm trying to learn how to take closer and clearer pics.....but this is the best i could do so far.....i don't know whether to be concerned or not!

the dots are not raised at all, they are flush with the leaf

My one and only Dendrobium species in my collection also has those dots on the underside. They all appeared when I gave it very bright light (natural direct sunshine) about more than a year ago to initiate blooming and it worked, it spiked almost right away but those ugly dots appeared and it doesn't seem to hurt the plant. It is now back in bloom on 3 spikes, so I'm not complaining. I think mine was a result of sunburn.

dendrobiums, and other things in that tribe, have a tendency, i'm pretty sure, to have black spots on the leaves. if they're spots and not scales, then it's fine....

I wouldn't worry about it. I'm not sure what type of dendrobe it is, but mine get spots too...especially my nobile types when it gets cooler.

Do the spots wipe off with a little alcohol? If so, it's a sooty mold called botrytis. That's usually a result of a combination of high humidity, hot temperatures and inadequate air circulation.

i licked my finger and rubbed the leaf with it, and it rubbed off......the dots don't really.... but the stuff on the underside of the leaf does.....i did not try alcohal....i could though..

Do the spots wipe off with a little alcohol? If so, it's a sooty mold called botrytis. That's usually a result of a combination of high humidity, hot temperatures and inadequate air circulation.

I agree with phragfan. if not from high light level, then it is mold.
For a long time I collect dendrobium nobile, they came from hawaii, they all have black mold on & specially under the leaves from the moisture environment & the sugar that the plants exude.
I wash each plant with soap & water, most wash off, but some black discolor will stay on. I do not water the leaves just the root area. The problem clears up after some time.