Beginner Gardening: Mystery diseased houseplant needs serious help, 1 by newyellowroom

newyellowroom wrote:
This image is of the sorry houseplant my coworker owns. The plastic ID pick in the soil just says "tropical plant," and we don't know what kind it is. It has fine webbing throughout with tiny white particles and super tiny black particles, but no observable insects. Its mature leaves have a dusty-looking coating that doesn't wash off, and lots of them are dried up and dead on the edges.

It seems to have had a growth spurt recently and put out tons of spikey new leaves, but they never opened and growth halted. Lastly, it is really gangly and unattractive, but we don't know how much to cut it back. For all you houseplant experts: if this was your plant, what would you do? We need a plan of action!!

Thank you so much!
Heather