A mysterious Polemonium

Polemonium archibaldiae - in rather grey weather this afternoon.

Visiting Sibylle Kreutzberger for tea this afternoon I admired, as always about this time of year, her magnificent clump of the plant known to horticulture as Polemonium archibaldiae. It's a fine, robust, very perennial plant standing up to 60 cm, with a mass of soft purple flowers with golden anthers above neat foliage. Not only is it handsome, but it has the advantage of being sterile and continuing to flower for a long period: it really does deserve its RHS Award of Garden Merit. It's not easy to propagate, but I find that the new shoots will root and develop if they are detached from the base of the plant when very young in spring.

P. archibaldiae
in evening light

But what is it? A Jacob's Ladder from Colorado was described as Polemonium archibaldae in 1901 by Aven Nelson, an early leading light in the University of Wyoming and a pioneer of the Rocky Mountain flora, but it was later treated as a subspecies of the common western American P. foliosissimum and the wild plant is probably, at best, no more than a form of this species.  Whether the cultivated plant bears any connection with "P. archibaldae" in the wild is impossible to say without doing a lot more research. I suspect we should really treat this garden plant as a clonal cultivar. The picture in cultivation is muddled by the occasional appearance of a white-flowered plant under this name (always rendered archibaldiae in horticulture,it seems) and although various authorities suggest the purple-flowered plant should bear the name, it's not inconceivable that a white-flowered selection was made of seed from a wild population.

PS (20 June 2011) A cut stem on the desk is releasing a strong scent reminiscent of sweet peas - another good feature of this plant.