I remember reading (can't remember where though) about a tapestry done in the late 15th c that showed different plants and flowers. The conservationist realized that a lot of the different flowers that were shown in bloom wouldn't be in bloom at the same time. Some were early spring flowers, others were late summer flowers. My guess is something similar is going on here. All the fruits are available in the region but not necessarily at the same time. I don't recall if there was a reason or if it was just artistic license.

EDIT: Found out it was the Unicorn Tapestry. They mention each plant is shown in it's prime (http://www.metmuseum.org/explore/Unicorn/unicorn_flora.htm) here. My guess is something similar though not necessarily for symbolism.