Most growers of this cultivar seem to regard it as an arilbred; its growth habit suggests it may be an RB+. Strangely, though, a chromosome count by Freeman Yendall (ASI Yearbook 1970) gave 2n=43, a result hard to explain if a set of TB chromosomes is present. I have therefore listed it among the tetraploid arils, although with considerable reservation. The flower is not typical of Iris stolonifera; there are no beards on the standards and the fall beards are very thick and bushy, as seen in bearded irises.
If a tetraploid aril, it would be expected to be fully fertile. In April of 2011, John Baumfalk posted to the SRGC forum
I am growing a seedling of Ed Pickin's that is "Turkish Topaz x At the Threshold". Turkish Topaz has never been fertile for anyone but Ed had not heard this.
Even if it is an unbalanced tetraploid, it may produce AA gametes and thus act as a tetraploid on occasion. It does produce normal-looking anthers with plentiful pollen. However, I have never had a successful cross with it. I eventually discarded it, as it seems strongly virus infected, is unsightly out of bloom, and seems to have little to offer compared with verified tetraploid Regelias.
Updated April 2016
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