I've researched honeydew and guttation and it doesnt look like either of them. They are solid and look and feel like salt granules. They are mainly on the stalks although there are a few here and there along the edge of the leaves. It is exposed to light with average heat and humidity. The plant looks healthy but there are a couple of leaves with portions gone. The underside of the leaves are clean. I haven't found anything that describes it.
Unfortunately, your photo did not come through. I am unable to see the damage.
It sounds like sap has been brought out at one point, and it has hardened. This can be caused by so many things, so unless you can see what caused it, then it may be impossible to determine.
In the meantime, here is an article that will give you insight into their proper care requirements:
Hi, I bought 40 plugs of Busy Lizzies, some of them have dark red / purple / brown funny shaped marks on the underside of their leaves - see photo. Please help! What is it? Is it just a normal pattern on the leaves or is it diseased? Many thanks.
This appears to be the beginning of an infection! Likely the plugs have been kept a little too moist, and too close together.
I would recommend a fungicide/bactericide. These articles will help:
my impatients are blooming like crazy but the plants have grown very little in six weeks
It wouldn't hurt. They are heavy feeders and require constant fertilization. This article will help you to grow the flower:
My property borders the woods The plants (impatiens) face east, but trees provide shade. Gets some sunlight
Are they getting sufficient water? When temps reach above 85 degrees F they need 4 inches a week. Have they gotten leggy? If so, cut them back by about 1/3. They should resume blooming in a couple weeks.
Review these cultural needs and see if they are being met. I usually supply regular water and a slow-release fertilizer a couple times during the year and they bloom all summer.
Hi- I grew a few impatiens from seed in a container. They have grown as tall as a foot but are very yellow and not strong. There are no leaves except for at the very top and I have gotten a couple of blossoms. Literally no leaves other than at the very top. What can I do?
Pinch off the growing tips to force them to branch out. Also, if you haven't fertilized them, give them a balanced fertilizer like 10-10-10.
I have an impatiens plant in my house that is getting very spindly. How can I cut it back and replant it?
Impatiens are easy to cut back. You can cut the stems back above a node by about 1/3 the length of the stem. They will grow back quickly and fuller.
I've great luck with a large variety of imapatiens. This summer after a number of years the plants seem to be dying. Do they need pruning or replacement? Thank you.
I see you are in zone 10 which can get down to 30 in the winter. That may take a toll on them each year. You might try cutting them back by about half and see if they invigorate. Also, be sure to keep the soil moist and fertilize monthly with a low nitrogen plant food. If they don't bounce back, go ahead and replace them. They look like New Guinea impatiens, so I am including an article about their care.