One of them was sold for $ 840K including premium by Christie's on December 15, 2010 over a lower estimate of $ 400K. This unit is now estimated $ 600K for sale by Sotheby's in New York on December 14, lot 447.
The discussion below is based on my 2010 post to which I added more recent results. The prices below include the premium.
The Wisteria is one of the most famous and sought after lamps by Tiffany Studios. It is a table lamp 70 cm high composed of a shade 49 cm in diameter made of a multitude of small pieces of brightly colored glass and of a bronze foot.
Designed in 1901, this model is inspired by botany. The foot looks like a gnarled trunk extended with protruding roots, and the bell shaped shade falls in hemmed clusters like a wisteria. Auction catalogs generally date these productions circa 1905.
At Sotheby's on 14 December 2007, a wisteria lamp was sold for $ 880K. Also at Sotheby's, another wisteria reached $ 600K on June 14, 2008 while a copy with the same shade design but other colors fetched $ 930K under the name of Apple Blossom.
In the Christie's sale on December 15, 2010 already referred here above, another wisteria lamp was sold for $ 480K over a lower estimate of $ 350K. I commented after the sale that both units certainly had some difference in quality since there was a difference of $ 50K in their estimates but exceptional lots widen the gap.
Another Wisteria lamp was sold for $ 1.56M including premium by Sotheby's on December 18, 2013. Two Wisteria with adjacent serial numbers were sold separately by Sotheby's for $ 1.2M and 1.15M respectively on December 17, 2014.