Merging these together gave me the trunk (Fig.07).
For the pod on top, I started with a Polygon Sphere. I copied lines onto every vertex of the sphere and adjusted the scaling using a Noise and Bounding box function. Then I gave it thickness using a polywire. I also modeled some additional detail and had it randomly copied over the sphere (Fig.08).
I drew a curving line around the sphere to work as a vine surrounding the pod. I then deformed the line using turbulent noise VOP and copied it randomly around the sphere using a Copy SOP (Fig.09).
Finally I merged it all together and attached the sphere to the top of the central line (Fig.10).
The final completed tree looked like this (Fig.11).
Since everything was deforming around the central curve, if any changes were to be made to the curve the entire tree could be readjusted.
To create the clump of three trees, I used a bit of Houdini magic:
I drew three central curves, put them in a Switch SOP and fed it into the Wiredeform SOP. Then, using a Copy SOP and a Stamp function, I made Houdini switch between every consecutive curve for every copy (e.g: copy 1 would use curve 1, copy 2 would use curve 2 and so on). This made creating variations even simpler (Fig.12).