According to traditional usage, the easiest way to distinguish between these 3 species/ varieties is to look at the color of the flower, especially the lip.
caudatum - greenish-yellow flower, lip greenish-yellow with brown near the rim ex. http://www.slipperorchids.info/phragspecies/Phragcaudatum1.jpg wallisii - yellowish flower, lip creamy ex. http://www.slipperorchids.info/phragspecies/Phragwallisii2.jpg warscewiczianum - yellowish-brown flower, lip with yellowish background and a very dark brown area near the rim. ex. http://www.slipperorchids.info/phragspecies/Phragwarscewiczianum3.jpg There is a newer version of the above key detailed in: Braem, G.J., S. Ohlund, and R.-J. Quene. "Will the Real Phragmipedium warszewiczianum Please Stand Up?" Australian Orchid Review 70, no. 6 (Dec/Jan 2004-05): 4-15. According to that article, Phrag. caudatum is the same as above, Phrag. warscewiczianum is now the proper name for Phrag. wallisii above and Phrag. wallisii is reduced to the synonomy of Phrag. warscewiczianum. A new species, Phrag. popowii, is described to take the place of what used to be Phrag. warscewiczianum. (I think this is how it goes, but Dr. Braem would be the one to ask). For the most part, the traditional names are still used, but if purchasing a plant of any of the three it would probably be best to ask to make sure which taxon you're getting. --Stephen _______________________________________________ the OrchidGuide Digest (OGD) [email protected] http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com
