Yup, that's my thinking too.
The spikes are a wonderful mashup of visual design elements : texture like mussels growing on a worn pier support -
http://i.imgur.com/fBIBVMc.jpg
- but when you see the 'mussels' up close, they're not sea creatures at all, they're fruits!
The 'unripe' ones look like cocoa pods growing from a tree trunk, but as they ripen, they look more like cape gooseberries (physalis) wating to open.
http://i.imgur.com/jrWEQHp.jpg
The skin of the pod is more like snakeskin though - not unlike the salak fruit in fact -
http://i.imgur.com/AVaLtMI.jpg
http://i.imgur.com/6LE9JoX.jpg
It's clear the metal-bearing pods ripen as the 'tree' grows, and the ripe pod contains
meta-alloys.
Which leaves the barnacle - what is its purpose?
I believe it's a combination of hopper and control centre. First, the barnacle is planted, then it causes trees to sprout around it. The trees mine metals, refine them, then combine them in the fruit pods.
Finally, the barnacle collects the ripe meta-alloy fruits and stores them in the armoured central structure, waiting for the farmer to return and collect the harvest.