It is difficult to tell the difference between Tillandsia jucunda and Tillandsia ixioides, in fact they are listed next to each other in Smith and Downs, numbers 172 and 173. However, if you have them flowering at the same time it is easy to tell them apart because Tillandsia jucunda has the paler yellow flowers, is scented, and the floral bracts are pinkish instead of grey papery. If you want to look further, all the sepals on Tillandsia jucunda are virtually free.
In 1992 I was "induced" to purchase a Tillandsia ixioides var occidentalis in the USA because I was assured that this was the old name for Rauh's Tillandsia jucunda v. viridiflora.
Perhaps I should have known better because at the time I knew that Tillandsia xiphioides v. tafiensis had blue petals and could be found in habitat, in Germany and in Australia. Only the white flowered form was for sale in the USA because they didn't know where the proper blue-flowered one could be found!! Anyway, in 1994 my Tillandsia ixioides v. occidentalis flowered with beautiful yellow flowers as it should but not according to the sales spiel! In the meantime I obtained a Tillandsia jucunda v. viridiflora from Germany and await green flowers.
A couple of years ago, Keith Bradtberg in South Australia told me he had a blue flowered Tillandsia jucunda which meant he had to give me an offset! The original plant had come from Rolly Reilly and no doubt was seed raised. My offset has just flowered and yes, the petals are the palest of blue which came out the purest of white in a photograph! I have dissected it and it agrees with the description of a Tillandsia jucunda except petal colour and my wife, Margaret, says it has a scent. (Remember human females are more reliable in this regard than human males.)
Now, I know you purists are going to say "Hybrid" but Mark Dimmitt from Tucson, Arizona USA who does lots of Tillandsia hybrids did mention to me that he believed Tillandsia jucunda was itself a hybrid. So I am hedging my bets by calling the plant Tillandsia jucunda cv 'Blue Rinse'. (Now T. 'Blue Rinse') Why am I telling you this? Well, Rolly Reilly does come from your neck of the woods and there could be other 'Blue Rinse's around. Mind you he may also have produced a red petalled form and then we would have all the colours and I wouldn't be behind the black ball.
Notes added July 2005
Since then I have come across an alleged crossing of bergeri x tenuifolia by Rolly Reilly which produced a bright yellow petalled plant – now called 'Marie' showing the involvement of T. ixioides and a white petalled plant – now called 'Marie White'.