I had these this year as well. It looked like tiny black coffee grounds covering my lilies. It turned out they were black aphids. I purchased live lady bugs and they ate them up. Good luck!

Possibly maple scale. I remove them manually but my maples aren't that big. There is probably some spray you can use if you believe in better living through chemistry. Some type of scale seems to occur in limited amount on my maples yearly - but they seem to do limited damage (I do give some of them the shaft)

Thank you, everyone! I do think it's scale (warning: very last photo will be an icky picture of my scrapings—this is as close as I could get, floral :T ). They came off like flakes with little weight, actually, with the nudge of a plastic knife. I immediately sprayed both the inside of its shell and where it had been attached to the tree in case crawlers were coming out in a frenzy from either. Litterbuggy, to provide more info (that pics alone can't provide!): We will try the chopstick! We had previously been sticking a finger in / using a meter. The potting mix isn't typical peat moss + perlite; it's fast-draining succulent mix with perlite. Does this look coarse enough? We live in Orange County so it's desert-dry; I mist it some mornings. Our temperature stays around 78°F with the AC off while we're gone. Air doesn't move much. And our tap water is indeed pretty hard. Still have little budding green shoots on nearly every stem. Most leaf stems are still upright; only some droop, especially this one trunk stem: My two top concerns now... I'm now worried every little brown speck on the trunk is scale... Should I be? The tops of each trunk/stem are dark; since every one was that way (and has been for a while), it didn't occur to me that might be unhealthy. Is that of great concern? Gross photo alert. It's so dark you can't really see much...

Looks like a type of Opuntia. Maybe similar to O. schickendantzii. Not sure of the species, normal growth habit, or price though.