Pumpkinvine: A relatively small, multi-level track plan that loops and twists and turns from plains to summits and back again.
Usage: Sally's 0-4-0 wasn't powerful enough to haul the four boxcars through Bob's Pumpkinvine layout.
Source: Bill Schopp, in his guise as The Layout Doctor, introduced the term in the May 1953 issue of Railroad Model Craftsman in an article called, naturally enough, Pumpkinvine Layouts:
When it comes to getting a lot of multi-level mountain railroading in a small space in HO gauge, I've yet to find a layout idea that works out better than what I call the Pumpkinvine, exemplified by the three designs here.
In essence, a classic Pumpkinvine track plan is based on a figure-8 with extended looping that climbs up and has at least three levels. The climbs are usually up through mountainous terrain. Mr. Schopp shows that a viable layout can be built in as little space as 4' x 10'.
Even though multi-level mountain spectacles are easily created with the Pumpkinvine approach, there are drawbacks:
The one big disadvantage is that there is usually very little space for any sort of town, so you have to imagine that they are in that mystic geographic area just off your platform. It is quite difficult, too, to work in many industrial sidings yet have all switches accessible from the front.
The Pumpkinvine is not to be confused with either the omnivagant or spaghetti layout.
from The Dictionary of Non-Existent Model Railroad Terms, 1st ed.,1959.