When a subspecies has varieties .......

[Moose]

..... what is the naming convention? Here is info taken from the CBIF website. I would have though that the scientific name for a variety of a subspecies should reflect that
eg Sambucus racemosa ssp pubens var arborescens.

Subspecies Sambucus racemosa ssp. pubens
- 5 records modified since 26-April -2011
- contains 5 accepted taxa ( 5 verified - standards met)

- down one level
Get the following data in XML format
Variety Sambucus racemosa var. arborescens
Variety Sambucus racemosa var. leucocarpa
Variety Sambucus racemosa var. melanocarpa
Variety Sambucus racemosa var. microbotrys
Variety Sambucus racemosa var. pubens

[Daniel Mosquin]

You can read this discussion on Wikipedia, which I think addresses the issue you are hinting at.

In brief, quadrinomials can be shared to give classifications, but only trinomials are accepted as names according to ICBN 24.1.