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Julian Sutton & Dan Crowley (2020)
Sutton, J. & Crowley, D. (2020), 'Carya ovata' from the website Trees and Shrubs Online (treesandshrubsonline.
Large tree to 46 m in the wild. Bark pale grey, fissured, exfoliating in long strips or broad plates, persisting and curling away from stem. Branchlets greenish to brown, stout or slender, glabrous or pubescent. Terminal bud ovoid, 0.6–1.8 cm long, tan to black, glabrous or tomentose. Leaves deciduous, imparipinnate, 20–36 cm long (larger in vigourous, young trees); leaflets (3–)5(–7), ovate to obovate or elliptic, 4–26 × 1–14 cm, upper surface largely glabrous; lower surface hirsute with simple and 2–4-armed hairs, occasionally restricted to midvein and primary veins or nearly glabrous, with few to many large peltate scales and small round, irregular, and 4-lobed peltate scales; margins finely to coarsely serrate, with tufts of hair in axils of serrations at first, often largely lost later on, apex acute to acuminate; lateral petiolules 0–0.1 cm long, terminal petiolules 0.3–1.7 cm; petiole and rachis sparsely to densely hirsute and scaly; petiole 4–13 cm long. Male catkins to 13 cm long. Fruits brown to reddish-brown, 3–4 × 2–3 cm, globose, sometimes depressed, not compressed, splitting to the base; nuts finely wrinkled. (Whittemore & Stone 1997; Whittemore 2013).
Distribution Canada Southern Ontario and Quebec Mexico North west (as var. mexicana) United States Eastern states, absent from Florida
Habitat Wet bottomlands, rocky hillsides, and limestone outcrops.
USDA Hardiness Zone 4-8
RHS Hardiness Rating H6
Conservation status Least concern (LC)
Very widespread in the wild and seen relatively often in European collections, a ‘typical’ mature Shagbark Hickory is not hard to identify. This is however a variable species, and one which hybridises widely and freely. Less than typical specimens are frequent: some may be hybrids, some not. It can be difficult or impossible safely to identify certain individuals (Andrews 2006). Even without worthwhile nut crops (yields are very poor in the United Kingdom, for example) this can be an attractive landscape tree with light green foliage in summer and excellent yellow autumn colour. It typically forms a narrow crown with ascending upper and descending lower branches. It suits a well-drained site, tolerating poor and metal-polluted soils (Andrews 2006) and has a particularly long tap root, leading to the usual issues around transplanting hickories.
The overlapping scales of the terminal bud show C. ovata to be a true hickory; the buds can be large and conspicuous. The species is fairly well-distinguishable by its shaggy bark and leaves made up of (usually) five leaflets. Manning (1950) states that the tufts of hairs on the leaflet serrations of C. ovata are one of the best characters for identifying this species, whilst acknowledging that this character varies somewhat through the seasons. In spring, the serrate margins are themselves ciliate: the tufts are still evident but they become more obvious once these hairs have fallen, though by autumn the tufts themselves may have worn off Manning (1950). Manning does admit that some specimens he studied, which otherwise appear to be C. ovata, lack this feature; this may of course be down to a non-typical herbarium specimen being collected from an individual. As with all species of Carya, extreme care is advised when making identifications and a number of leaves should be studied in order to establish the presence/absence of this feature. The shaggy bark could be confused with that of C. laciniosa. Dirr (2009) that the plates are usually more pronounced in C. ovata, with the free ends and edges more recurved. ‘Shagging’ is not apparent in young trunks, usually becoming visible by 30–40 years old (J. Sutton, pers. obs. of UK cultivated material). A few individuals, both in cultivation and the wild, seem to retain smooth bark at maturity: it is unclear whether these are hybrids (Andrews 2006).
Shagbark Hickory is an valuable timber tree across its native range, and is the most prized of the true hickories for its nuts. Sapwood (‘white hickory’) is favoured over heartwood (‘red hickory’). It is strong, extremely shock resistant, and used for tool handles and baseball bats (Grauke 2003). Dense, an excellent firewood, it is one candidate for the best meat-smoking hickory: for smoking, the wood is used green. Indigenous peoples ate the nuts and used various parts of the tree as medicine; the Omaha and Pawnee tapped the sap to make sugar, as for maple syrup (Moerman 2019). 18th-century observations hint that a hickory, probably C. ovata, may have been cultivated by Native Americans in Georgia (Grauke 2003). Nuts are harvested today, from wild and cultivated trees, but not on a seriously commercial scale.
Cultivated in Europe since 1629 (Armitage et al. 2014), C. ovata was grown in the Tradescants’ garden at South Lambeth, London (Spongberg 1990). Elwes & Henry (1908) concluded that the species was not very long-lived in the Unied Kingdom, as none of the trees mentioned by Loudon (1844) were still alive. Larger trees are scattered across the British Isles, with a strong concentration in southern and central England. Outside of the most serious collections of Juglandaceae, such as those at Kew and Westonbirt where there are beautiful examples, received identifications should always be approached with an open mind and open eyes. Especially large specimens include one on the Reading University campus, apparently a tree known to Elwes & Henry (1908), measured at 17.5 m × 92 cm in 2016, and one at Hollycombe, West Sussex (29.5 m × 45 cm in 2018 – The Tree Register 2019).
In continental Europe, this species is recorded quite widely from Belgium and The Netherlands east to Belarus, with good specimens in the park around the Kasteel Vilain XIIII, Leut, Belgium (26 m in 2016) and in the rather mild climate of the Dendrological Garden at Glinna, north west Poland (31 m in 2015, a beautifully formed tree – monumentaltrees.com 2019). Two wild origin specimens from a 1970 accession are well established at Gothenburg Botanical Garden, Sweden (Gothenburg Botanical Garden 2019). Outside its natural range in North America, the Shagbark Hickory can be grown in the Pacific Northwest, with examples in the Hoyt Arboretum, Portland, OR and the University of British Columbia Botanical Garden (Hoyt Arboretum 2019; University of British Columbia 2019).
Over 130 ‘cultivars’ have been named, but many of these names were simply labels given to individuals singled out for their nut qualities; few have ever been propagated, and many no longer exist. Selection has focused on yield, cracking quality and kernel size, but a dual focus on timber and nuts would be beneficial (Grauke 2003). Where cultivars have been propagated, this is sometimes merely by seed, but increasingly by grafting. In southern Ontario, Grimo Nut Nursery (2019) finds Pecan a better rootstock than C. ovata itself. Male and female flowers are usually fertile at different times, even though cultivars are not usually described as protandrous or protogynous. Planting two or more varieties together is the norm, a minimum of three where one is male-sterile. Here we list a few cultivars suitable for more northerly areas, which are available from nurseries on both sides of the Atlantic.
Introduced in 1934 by John Hershey, Dowingtown, Pennslyvania. from a farm in Grainger County, Tennessee. It suits colder northern areas and is reported to be very tolerant of alkaline soils. Nuts are very large, approaching the size of a Shellbark, tend to fall free of the husk and crack well. It is a good pollinator for other Shagbark varieties (Crawford 2016; Grauke 2019; Grimo Nut Nursery 2019, De Smallekamp 2019).
A northern variety, originating near Waterford in the far south of Ontario, ‘Neilson’ is suitable for colder areas. It is precocious, regular and very early fruiting but is male-sterile, so another pollinator (and perhaps a third to pollinate the pollinator!) is absolutely necessary for nut production. Nuts are medium to large, crack fairly well and tend to fall free of the husk. Named in 1934 by J.H. Corsan for Jas Neilson of Waterford (Crawford 2016; Grauke 2019; Grimo Nut Nursery 2019).
Carya carolinae-septentrionalis (Ashe) Engl. & Graebn.
Var. australis has slender, glabrous branchlets that turn black when they fall. Terminal buds reddish-brown to black and largely glabrous. Leaves 20–30 cm long; leaflets 4–19 × 1–6.5 cm. Male catkins to 6 cm long. Fruits 2.5–3 cm long and wide. In comparison, the nominate var. ovata has stout, hirsute branchlets that retain their colour when they fall. Terminal buds tan to dark brown and tomentose. Leaves 30–60 cm long; leaflets 6–26 × 3–14 cm. Male catkins to 13 cm long. Fruits 3.5–4 cm long and wide. (Stone & Whittemore 1997; Schaarschmidt 2002).
RHS Hardiness Rating: H4
USDA Hardiness Zone: 5
Carya ovata var. australis is occasionally found in American collections, including one very fine umbrageous specimen at the Morris Arboretum, Pennsylvania (labelled Carya carolinae-septentrionalis), planted by John Morris some time between 1887 and 1915. This tree was measured at 30 m × 92 cm (2009). A seedling from it is growing at Wakehurst and is the UK champion, measured at 5 m tall in 2018 (The Tree Register 2019). The bark of the parent swirls in longitudinal plates and fissures, and is in itself a complete justification for planting it, never mind its other fine qualities such as turning gold in autumn (Grimshaw & Bayton 2009).
A second variety, var. mexicana (Hemsley) W.E. Manning is confined to Mexico and appears to be grown only at the Mediterranean-climate margin of our area at the University of California Botanical Garden, Berkeley (University of California Botanical Garden 2019).
Selected by Carl Weschcke of Wisconsin in 1926 from a tree in Fayette, Iowa, this is a suitable variety for colder northern areas. It is both precocious and early ripening, a productive annual bearer, but is male sterile. As a result a minimum of two other cultivars should be planted alongside it to ensure pollination for all three trees. The nut is relatively small but thin shelled; it is among the best for releasing the kernel easily in two neat pieces (Crawford 2016; Grauke 2019; Grimo Nut Nursery 2019, De Smallekamp 2019).
Selected by Emmet Yoder in Smithfield, Ohio, this is a variety for northern areas, but perhaps not the very coldest. Precocious and cropping heavily in about two out of three years, it is usually one of the later varieties to ripen. It is fully fertile and hence a good pollinator for the choice but male-sterile forms. The medium-sized nuts crack well (Crawford 2016; Grauke 2019; Grimo Nut Nursery 2019; De Smallekamp 2019).