Is brown spotting and freckled leaves normal on Oncidiinae plants?

[King_of_orchid_growing:)]

Originally Posted by Ray

Philip.

There are stomata on both surfaces of all orchid leaves.

Is there evidence for this? If there is that'd be awesome.

I am looking at my Oncidium peltiforme leaf under a microscope. Granted the microscope is not very good, (it is a student microscope), I can find the stomata and the guard cells on the underside of the leaf pretty easily. I even saw one that was open. When looking at the top portion of the leaf, I hardly saw anything I would call a stomata with guard cells.

The photo attached shows what the guard cells look like and where a stomata would be. In this photo, there are two bean shaped areas on either side of the black arrow. Those are the guard cells, and the stomata are closed. This was taken on the underside of the leaf. There were tons of these structures on the underside. This was at 100x magnification.

I know that the guard cells and stomata are difficult to see because my microscope sucks and this was taken from an intact, living Oncidium peltiforme, but they are there.

The second photo is also 100 x magnification and is of the top surface of the leaf. I had a very difficult time spotting what would be considered a stomata or guard cells. I’m not saying that this is conclusive evidence, (partly because the microscope used is pretty terrible), but it is evidence that is at the very least pointing to stomata being far more prevalent on the underside of an Oncidium peltiforme leaf compared to that on the topside of the leaf. If there is anyone out there with a better microscope than mine, please feel free to show us what you’ve observed as far as Oncidium leaves are concerned.

If anyone wants to know, I just took these today a few minutes ago. I didn't prepare any slides for this photo, nor did I cut any part of the leaf off.

Since the black spotting is prevalent on both top and bottom parts of the leaf, and there seems to be a lot of stomata present on the underside of the leaf, but if there are stomata on the topside of the leaf, they are extremely sparse, I don't know if I can definitively say that the black spotting we're talking about is a result of salt buildup around stomata.

[Ray]

Philip, I don't have any specific references at hand, but if I recall correctly, several articles I've read concerning C3, C4, and CAM metabolisms in orchids discuss the placement and density of stomata on leaf surfaces.