[Editor's note: Technology advances have allowed me to replace the original photo with the higher quality one, shown below and taken by Fiona Woolfenden]
The armandii cultivars are some of the earliest flowering clematis and were first introduced by E.H.Wilson from China in 1900, it was named after Pere Armand David, the French missionary and plant collector.
It is an evergreen with large waxy hard leaves which rattle in the wind. Best planted against a warm wall where it will be protected from frosts which may damage its flowers. The younger leaves are bronzen and look attractive. The plant can suffer from sap sucking insects.
There are two main armandii clones available: C. 'Apple Blossom' and C. 'Snowdrift'. A trial at East Malling Research Station, Great Britain, showed that over the years different plants and seedlings have been wrongly named. There is a picture of a number of the trial varieties in the I.Cl.S. Journal 1990, available free to new members whilst stocks last. The difference is that 'Apple Blossom' has rounder tepals (petals) and is pinker in colour while 'Snowdrift' has sharper and thinner tepals and is a white with a hint of green. Both varieties can be scented depending on the stock.
My plant of C. 'Apple Blossom', pictured above, is planted in a tub on my south-facing patio and grows up a east-facing fence. It gives me lovely early flowers with a wonderful vanilla scent. Unfortunately, it also suffers from scale insects.
In the UK, C. armandii flowers late March through to early April and grows to about 6 metres. The flowers are about 5 cm across. In the USA, it grows in the southern part of hardiness zone 6 through to hardiness zone 9.
Opinions are divided on whether C. armandii should be pruned. It can be chopped to the ground and survive. It can also be pruned after flowering to encourage new growth. Alternatively it can be left and will continue growing, though the older leaves will discolour and will have to be removed.