tap water?

Likely residue from guttation. If so, getting rained on should remove it, but don't forget it's outside. This plant burns very easily.

Taste it, if it's sweet then it is possibly guttation. It could also just be dust sticking to the moisture from excessive transpiration. Could be hard water scale if they were misting or hosing off the plants.

Either hose it off or give it a good shower for a few minutes and let it dry up and see if it goes away. You might need to gently rub the leaves between your fingers.

Then, after it dries, if it is still there explore other more troubling issues like fungus.

Wonder if the "black crud" was actually the velvet covering coming off..?

I'd suspect it's just water stains, minerals out of dried up water, the way it collects along the leaf margin. Fungus usually kills off plant tissue below and that would show.

Philodendron hederaceum var. hederaceum is the correct name, P. micans is a synonym.

Hi gang.

I always thought that for some time micans was thought to be it's own kind of philo but later the powers that be stated that it had been a hederaceum like the others(like those called oxicardium and medio-picta for example) all along only showing different traits in a similar way to people(the comparison I seem to remember),in that although we come in different shapes,sizes,colors etc.,we are all homo sapiens sapiens.

Like mentioned upthread,I'd be curious to know if you were getting your water,Jess...come back when you can,okay? :)

Hi all,
Thanks for all the helpful suggestions! I tasted it and I can't say it tastes sweet so probably not guttation. It would not surprise me at all if Lowe's was misting or watering the plants with a hose so I can definitely see it being hard water scale or mineral deposits. The leaves look very healthy and don't seem to show any signs of tissue damage. Asleep, I haven't had the chance to give them a proper shower yet, but in the next day or two I think I will, and it could be that I rubbed the velvet coating off with the q-tip. Also good to know the correct name of the plant! :-)

Hi Danny..Do you make it a habit tasting plants? Gutation or other fluids?
Please be careful.
Even if a plant isn't toxic, some ppl have allergic reactions.

Asleep. I'm perplexed. Why would purple velvet come off? I honestly don't understand.
If purple was washed off entirely, would the leaf be green?

Hi Toni, I don't as a rule but I have a number of drippy aroids and get the stuff all over me whenever I get around them. Two of my philodendrons drip so much that I won't even touch them, I use tweezers or gloves if I need to handle them.

Tropic makes a good point about tissue damage too.

Oh hi Toni!

Jess said: "It scratches off with my fingernail (I only tried gently doing this on one leaf) and wetting a q-tip and running it over the spots gets a lot of nasty dark crud off the leaves, but the white remains."

That's pretty much what I was getting at,..I figured the nasty dark crud was velvet coming off the leaf where she had run it over spots. :)

My plant has the same residue at the tips. It doesn't get misted, or showered (or watered) with tap water. The leaves on this plant are extremely easy to damage, I try not to touch them at all except when I'm guiding the vines up their little trellis.