The identification of Arisaema species   

The main problem in the identification of Arisaema species is that there is more than the usual degree of uncertainty in the nomenclature. It's not just the usual case of nurseries selling plants under an incorrect name, (and, reportedly, refusing to correct the errors when they're pointed out!), but that there is some uncertainty amongst growers: particularly with regard to forms and cultivars.

However, we can't do much about that other than be very careful that we are quite sure of the correct identity of the material we have; paricularly if passing it on or selling it.

There are a number of taxonomy keys available on-line. [1] [2] [3]

The two keys by Murata et al are not the same. It's difficult to find a date for the first one, as it's part of a draft document which covers all of the Aroids, but the second version was published in 2010.

The Gusman et al document was published in 2005 and is complicated by the fact that the intial selection is based on the geographic distribution of the plants of which you may not be aware. However, it does have the advantage that it has interactive links to the various sections.

[1] Gusman et al key
[2] Murata et al key 1
[3] Murata et al key 2, Fl. China 23: 43-69. 2010.