Clematis 'Isca' is a beautiful semi evergreen winter flowering clematis that is quite rare to find. It flowers from November to February although the flowering season can start as late as December. It is a C. cirrhosa/napaulensis hybrid raised prior to 2007 by the great clematis hybridiser, Barry Fretwell, and first sold by the German Westphal Clematis nursery, who described it as a a hybrid of C. cirrhosa with an unknown clematis raised by Barry Fretwell. These days commercial hybridisers rarely divulge the parentage of their crossings and Barry has kept these details to himself. However I think it's fairly safe to make an educated guess that one of the parents is C. napaulensis given that the filaments and anthers of C. 'Isca' are pink-red which are characteristics of C. napaulensis and not naturally found in C. cirrhosa variants. There is also a marked similarity of C. 'Isca's' leaves with those of C. napaulensis. As for being able to accurately identify the exact C. cirrhosa parent, that is less certain but hazarding a guess based on the pale-yellow flowers that mature to creamy-white but lack any speckling, and the shape of the flowers, I would venture a possible parent as C. cirrhosa 'Wisley Cream'. I first came across C. 'Isca' in 2015 when I saw it advertised in Westphal's on-line clematis catalogue. I have always had an affection for the Cirrhossa Group variants and this plant looked quite special with it's nodding bell shaped flowers with striking pinky red stamens so I ordered one, together with C. 'Halcyon', another beautiful C. cirrhosa/napaulensis hybrid also raised by Barry. C. 'Isca' as you would expect displays typical Cirrhosa Group characteristics which means that it becomes dormant during the summer months from June to August, losing its foliage and looking dead to all intents and purposes. Please bear this in mind when deciding where to plant it. Nevertheless, despite it's appearance the plant is not dead and should be watered judiciously until September when new leaves will appear and simultaneously tiny hanging flower buds start to form on the previous season's growth. During it's dormancy period I have found that in order to maximise flower development when it comes back to life it helps to give the plant a top dressing with home-made garden compost. At the point when it springs back to life it's also beneficial to feed sparingly every couple of weeks with a weak solution of tomato fertiliser.
In November/December the pale-yellow flowers open in ones and twos or groups of three and four and although small at 2-3 cms in diameter, they more than compensate with their very attractive pinky red stamens. An interesting feature is that the bracteoles are joined to the top of the flower like a pair of tiny green leaves, again suggestive of C. napaulensis heritage. The flowers also contain a lot of sticky nectar to attract insects. Flowering continues until January/February and then the plant continues to put on growth until it senses the rising temperature of summer when it sheds it's leaves and enters a period of dormancy. It is genetically programmed to do this because the native habitats of both parent plants have typically hot dry summers and mild wet winters. Typical height is about 2-3 metres so it's not difficult to find a place for the plant. My experience of growing C. 'Isca' in our garden in Leeds, West Yorkshire, England is that it is reasonably hardy as for the last six years it has survived average winter temperatures as low as -5°C and the flowers seem unaffected by snow and ice. However to do well, like all Cirrhosa Group cultivars, it needs a sunny well draining sheltered position away from cold winds.
C. 'Isca' - two blooms
C. 'Isca' - buds and bloom
C. 'Isca' - demonstrating the size
C. 'Isca' - cluster
The International Clematis Register and Checklist 2002 Sixth Supplement (published 2018) gives the following information about C. 'Isca':
C. 'Isca' - a mass of blooms'Isca' Cirrhosa Group[Editor's note: I understand that C. 'Isca' is also being marketed as C. 'Christmas Surprise'.]
Parentage: napaulensis hybrid (× cirrhosa 'Wisley Cream'?)
R: B. Fretwell (pre–2007), I: F.M. Westphal Clematiskulturen (2013)
Syns: cirrhosa 'Isca'
Fls bell-shaped, 2–3cm across, pendent; pedicels red-brown. Sepals 4, opening pale yellow, maturing cream-white. Stamens numerous; filaments pink-red. Evergreen climber with stems 1–2m. FL: Nov–Jan/Feb, on previous season's wood.
Published refs: Westphal Hauptkatalog Clematis (2013): 13, as cirrhosa 'Isca' BFCCISC
External images: Westphal Hauptkatalog Clematis (2013): 13; The Clematis 2017: 105–108 "The same in leaf and habit as C. cirrhosa 'Halcyon'" (www.peverilclematis.com, 2007). Westphal's 2013 Hauptkatalog states "Clematis cirrhosa 'Isca' ist mit C. napaulensis gekreuzt worden" [C. cirrhosa 'Isca' has been crossed with C. napaulensis"], which is perhaps intended to mean that napaulensis is one of the parents of 'Isca'. Armitage, in The Clematis 2017: 105–108, suggests a putative parentage of napaulensis × cirrhosa 'Wisley Cream'. On both bases, it is recommended this cultivar be named C. 'Isca' rather than C. cirrhosa 'Isca'.