Otherwise known as groundcherries, Physalis are grown in warm, subtropical areas of the world.
The are quite similar to small tomatoes in size and shape.
So if we can eat them, can guinea pigs eat physalis and if they can how much of them can be eaten?
As per usual, lets take a look at their nutritional data in particular, their calcium, fat, sugar, phosphorus and acidic content.
image wikipedia

Calories53.0(222 kJ)3%
Total Carbohydrate11.2g4%
Total Fat0.7g1%
Vitamin A720IU14%
Vitamin C11.0mg18%
Vitamin B120.0mcg0%
Read More http://nutritiondata.self.com/facts/fruits-and-fruit-juices/1926/2/#ixzz2to0eSCJO
As you can see physalis contain a hint of phosphorus, calcium, and fat however they are quite acidic.
They also contain a decent amount of vitamin c.
So guinea pigs can eat physalis but only once or twice a week in small amounts due to their acidic content.