Rezzing Linden plants...but where do they go?

I'm so sorry for posting a thread about a question that has no doubt been posed and answered here a thousand times...but I've tried searching here and following the advice in those replies I've found and am still none the wiser.

I'm working in a skybox approx 400m up...and rezzing various plants, both Linden and other. All is fine until I try and rez the Linden 'leafy ground cover' plant - it gives me no error message and the prim count adjusts accordingly...but the plants are nowhere to be seen!

I have checked at ground level, I've checked using alt-ctrl-T, I've used the debug menu to check for 'buried objects'...and I've scanned the space between the ground and the skybox...heck, I've even walked away from the computer...left it for a few minutes and then jumped out on it in the hopes of finding the prims using the element of surprise....but I cannot find these pesky items.

Any advice, anyone? And returning items really isn't an option as I'm just 'dressing' the land in completion of a largescale building project! I did find a few days ago that after defragging my comp some long lost rezzed but never seen items reappeared...but I just reformatted the machine today so don't know if that could possibly have made any difference before or whether it would work again.

Thanks for helping...

Well...I took back everything into Inventory that I had rezzed in the same session as these elusive plants...they didn't show up but the prim count added up to them not being there anymore...and I've since checked and having rezzed the ground cover at ground level they won't move...so I think I've answered my own question.

The prim discrepancy will bug me for a while...but no doubt SL will soon come up with something new to distract me.

They rez at ground level, although sometimes they can end up underground as well.

I'm not sure which debug option you tried, but I'd use "Client / Disable Camera Constraints" to be able to cam around and underground, or "Client / Rendering / Types / SurfacePatch" (from memory so might be under a different sub-menu) to hide the actual land.