Vanessa,
If you'd like quantity in the labels, two labels is going to be your best option. Use connecting line or arc.
You could try putting them into a single concept design group and using the currently hidden setting of USERR1 = 1 to turn on full mleader concept labels, but you'd have to have a consistent breakdown of the sizes in each grouping. Like if in a group of 5, you always have 3 of one size and 2 of another, your percent fills for a concept tree with the 2 plants in the design group could be 40% and 60%, so when you label it the quantities are always 3 and 2. You could put the size in the plant name to have it show up until we implement some label improvements we're working on.
You could also do alphanumeric symbols for palms, with the size in the code. Alphanumeric Symbols
-Amanda