It looks like some kind of a fungal/bacterial infection.
I found this on Google:
Black spots on plants are usually caused by a fungal or bacterial infection called black spot disease. It can affect many types of plants, but it's especially common on fleshy-leaved plants like roses.
Symptoms
Black, round spots that appear on the upper sides of leaves
Spots may have feathery margins and be dark brown to black in color
Spots may start as pinheads and grow to be ½ inch in diameter
Infected leaves may turn yellow and fall off
Raised, purplish-red blotches may appear on one-year old canes
Causes
Black spot disease can be caused by a variety of fungi and bacteria, including Asterina, Diplotheca, and Glomerella
Black spot disease is more common in wet, humid conditions
Treatment
Spray the plant with a fungicide
Spray the plant with a mixture of water, baking soda, horticultural oil, and horticultural soap
Use neem oil, an all-natural fungicide
Prune plants to improve air circulation
Water early in the day so leaves can dry before night
Prevention
Inspect your garden regularly in the spring
Start preventative spraying before temperatures reach 60°F