Salix viminalis × S. caprea × S. cinerea (S. × calodendron
Wimm.), Holme Willow

Introduction, neophyte(?), deliberately planted, apparently very rare but probably under-recorded.

1833; Mackay, J.T.; Florencecourt estate.

In the Revised Typescript Flora, R.D. Meikle gave his opinion that Mackay's identification might possibly be correct, but he also made it clear that the specimens had not been located and expertly examined. Mackay (1836) listed it as S. acuminata Sm. (Long-leaved Osier) and stated that, "it had become a tree 20 feet high, although growing in an elevated position". It is still possible that a herbarium specimen may have survived, most likely in either TCD or DBN. The Revised Typescript Flora suggests that Mackay collected the plant from hedgerows and considered it either planted or an escape, but as far as we are aware this is merely surmise.

There are no subsequent records for Fermanagh of this tall, erect hybrid shrub or tree, the putative (but uncertain), parent species of which are the common shrubby sallows, S. caprea (Goat Willow), S. cinerea subsp. oleifolia (Rusty Willow) and S. viminalis (Osier), ie two native and one alien species. The hybrid exists as a purely female clone, probably a single genome, of necessity reproducing vegetatively. Stace et al. (2015) discuss the possible parentage of this hybrid in detail, without coming to a definitive conclusion. S. × calodendron is always imported and planted, rather than arising spontaneously where the parent species meet. The reasons for planting in the past are also uncertain, but it was most likely admired by some for its handsome, crowded, upwardly curved female catkins (Bean 1980).

While the specific epithet, calodendron, translates as, 'beautiful tree', Howitt & Howitt (1990) described it as the only ugly willow they know. These workers found that a small patch of S. × calodendron was grown in every English willow holt they had studied in the Trent valley, although they could not really fathom the reason why. One suggestion they made was that the timber of this hybrid is very easily longitudinally split, or it does so naturally once the branches reach a diameter of around 10 cm. It seems very likely that basket makers had a specific use for this split timber and accordingly they valued and cultivated this hybrid.

Although the date, place of origin and reason for introduction are all unknown and rather mysterious, the New Atlas editors still consider S. × calodendron as being a neophyte, ie an introduction of recent, or at least very probable post-1500 AD date. Their hectad map for Ireland shows the plant recorded almost exclusively in coastal areas, the major area on the island being the NE counties of Down and Antrim (H38 & H39). Mackay's old Fermanagh record represents a unique inland Irish station for this hybrid. In S England, there are numerous scattered examples of inland sites for the plant, again always planted.

In recent years, S. × calodendron plantation has been renewed for use as a biomass crop, managed on a short-rotation coppice for fuel (Stace et al. 2015).