This is a botanical variety, described by Engler in 1857, attention to which is drawn in Dr Guy Gusman's excellent monograph on Arisaema.
The spadix is very thickened and is white or purplish. It also flowers much later than the normal type. Although the the fruiting spike is said to be conical rather than cylindrical in this form, it appears that this is an observational difference only and it is actually due to age of the fruit spike.
We find that the tubers of this variety are naturally smaller and growth is both more slender and shorter than the type plant. A very worthwhile addition to a collection, readily grown and very distinctive.