In my opinion, originally this plant is a garden ornamental but I have seen it as an escape in some places by now. (Eg zabbar/m'scala near the traffic lights, 50m towards M'scala (left side).
I have also seen it growing extensivly next to the old Danish Village Hotel (near the Red Tower- Mellieha) as an undergrowth under the trees.
It also occured at Wied is- Sewda some years ago, which seemed to grow wildly, but it was then destroyed by fire if I'm not mistaken.
It surely is a garden escape.
Thank you for your information on Solandra grandiflora. I took the photo at the gate of GGANTIJA TEMPLE, Gozo Island. I now found that the flowers of S.longiflora and S. maxima are resp. used for stamps of Bermuda and Itutaki.
http://www.ne.jp/asahi/plant/stamps/sta ... naceae.htm