I just received this plant from a well respected eBay seller. The undersides of the leaves have many black spots, the smaller of which appear slightly indented. They look bacterial to me but I'd expect the plant to be in a very poor state were this the case. The plant otherwise seems healthy.
Have contacted the seller to see what they say. Anyone here have experience with these?
Monopodial orchids can get small sunken black spots like this when they aren't happy with the conditions. Usually the problem doesn't spread - if conditions improve.
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I doubt these spots are a worry. They could be the result of a lot of things but the tissue around them looks healthy. As ES pointed out, it's probably due to growing conditions. Keep an eye of the plant for further stress but don't worry too much about it.
I don't routinely give my orchids supplements, beyond fertiliser - wintergirl: how often would you give magnesium/calcium? When signs of deficiency appear?