Corylus × colurnoides Schneid.

A ‘Corylus intermedia’ was listed by the London nurseryman George Loddiges in his catalogue for 1836; Loudon believed this was a chance hybrid in cultivation between C. colurna and C. avellana (Bean 1981). The name C. intermedia had already been published in 1829 by Carl Fingerhuth for what is now called C. maxima (IPNI 2023), so Loddiges’ hybrid had to wait under 1906 for its own valid name, when Camillo Schneider described a cultivated tree at Hannoversch Münden in Germany as C. × colurnoides (Bean 1981; IPNI 2023). The same hybrid was not described from the wild until 1938, when the names C. × fominii (seed parent C. avellana) and C. × gudarethica (seed parent C. colurna) were published by the Georgian botanist Liubov Kemularia-Nathadze (Royal Botanic Gardens, Kew 2023; Holstein, Tamer & Weigend 2018) for a part of the little-studied wild hazel population of the Caucasus mountains.

The parent species belong to different sections of the genus and are not, in fact, at all easy to hybridise (Erdogan & Mehlenbacher 2000; Molnar 2011), and no putative crosses have been documented from any of the other areas where the natural ranges of Corylus avellana and C. colurna overlap; the two species also tend to occupy different habitats, with C. colurna able to tolerate hotter, drier sites. However, both hazels have been cultivated for so long that there have been several occasions, within gardens, when this unlikely union has taken place.

As an ornamental, C. × colurnoides is no improvement upon either parent. It generally lacks the straight trunk and imposing stature of C. colurna, though one in the Münster Botanical Garden in Germany is a tree 20 m tall; another, in the Botanical Garden of the Jagiellonian University, Kraków, Poland, has many trunks which radiate from a massive base (monumentaltrees.com 2023). An example in Meanwood Park (Leeds, UK) was apparently grafted onto C. colurna at ground level, above which it had two boles 59 cm and 51 cm dbh in 2004, and was perhaps a relic of the 1830s landscaping of the Meanwoodside estate, supplied by Loddiges; it blew down in 2013 (Tree Register 2023). The very few other known survivors in Britain are considerably younger and smaller.

This hybrid has attracted more interest for its potential in hazelnut production: the nuts are larger than those of C. colurna and of excellent quality, the tree is less likely to sprout unmanageably from the base than C. avellana, it is hardier than most selections derived from C. avellana and in North America can show a better resistance to Eastern Filbert Blight (EFB) and also to bud mites (Molnar 2011). The first breeder to take an interest in C. × colurnoides seems to have been Jack Gellatly, working in inland British Columbia through the middle decades of the twentieth century. Gellatly was growing C. colurna seedlings in large numbers – presumably for rootstocks – and was able to recognise the appearance of seedlings that seemed to be hybrids with the cold-hardy C. avellena clones that he had selected and grew (‘Craig’, ‘Holder’ and ‘Brag’). These crosses he called ‘Trazels’, and many of today’s commercially available C. × colurnoides clones are among those trialled by Gellatly. Gellatly also selected various seedlings which he suspected were C. × vilmorinii, calling these ‘Chinese Trazels’, but their morphology suggests that all these plants belong within C. × colurnoides. The open-pollinated putative C. × colurnoides clone ‘Filcorn’ was independently selected in the United States by O. Jemtegaard (Molnar 2011).

In 1990, two C. × colurnoides cultivars, ‘Newberg’ and ‘Dundee’, were released by Oregon State University for potential use as commercial hazel rootstocks; they had been selected from several thousand open-pollinated seedlings of C. colurna sown in 1971. Unfortunately, both these clones proved highly susceptible to EFB (Molnar 2011).

More recently, hazel breeders have turned their attention to back-crosses of C. × colurnoides with clones derived from C. avellana. In this account, the fruiting seletions within this group are summarised under the entry for perhaps the most prominent clone, C. ‘Grand Traverse’, while two ornamental productions with purplish leaves (C. ‘Rosita’ and C. ‘Ruby’) have their own entries.