Magnolia acuminata (L.) L.

Botanically challenging, Magnolia acuminata includes large, elegant, fast-growing and very hardy deciduous trees, as well as rather less hardy shrubs. It is highly significant in gardens across our area, both in its own right and as a parent of yellow-flowered hybrids.

Sitting alone in Section Tulipastrum, it shares its deciduous habit and mostly terminal flowers with members of Section Yulania, but is set apart by its North American rather than Asiatic distribution; by its buds opening later in the growing season, after leaf emergence; and by its blue/green or yellow rather than white/pink/purple inner tepals. Patterns of variation across its wide range have proved impossible to handle taxonomically to everybody’s satisfaction (see taxonomic note above). To say that hardier northern forms tend to be trees with glaucous-blue to green inner tepals (more rarely yellow), while southerly forms tend to be shrubs or smaller trees with yellow flowers is a crude simplification, but is a starting point, and is particularly useful when considering plants in cultivation outside North America, where only a limited range of material is grown. What follows here relates to typical northern tree forms, with southern shrubs discussed under var. subcordata.

This tree was well known to Native Americans and early European settlers, well before Linnaeus’ scientific description in 1759 (his specific epithet refers to the acuminate leaf tips). The Cherokee used its light, close-grained, yellow-brown wood for construction, furniture and paper making, while both the Cherokee and Iroquois had diverse medicinal uses for the bark (Moerman 2003). The rather small and insignificant flowers open on leafy shoots, typically with glaucous tepals, but colour forms range from ‘blue’ to yellow. Yellow-flowered forms sometimes named M. acuminata var. aurea Ashe have been collected from the Carolinas, Tennessee, Georgia, and possibly Alabama. These clearly have potential as parents in the creation of yellow, precocious flowering hybrids, although the acuminata parent of the original ‘Elizabeth’ had green outer tepals (Koerting 1977; Meyer 1997). The vernacular name refers to the shape and colour of the young fruits, which later turn red, but are not sufficiently large or numerous to rank as an ornamental feature. An alternative name, Indian-Bitter derives from François Michaux’s early 19th century report that indigenous poeple around the Allegheny Mountains steeped the unripe cones in whiskey to make a bitter tonic (Jacobson 1996). This can be one of the best magnolias for autumn colour, but varies between clones from a dull dark brown to bright yellow.

Its introduction to Europe is well documented, seed having been sent by the Anglo-American trader in seed of American plants John Bartram, in the 1730s or 40s, to his fellow Quaker the London draper and avant garde plantsman Peter Collinson; it first flowered for Collinson in 1762 (Bean 1981). Other European introductions surely followed, and the species was growing in Poland by 1820 (Anisko & Czekalski 1991). This is a very hardy tree, grown across most of our European area, north to southern Finland (Arboretum Mustila 2021) and central Norway (NTNU University Museum 2021). In the maritime climates of the British Isles, magnificent specimens at Wakehurst Place, W Sussex (22 m × 242 cm, 2015) and at The Hollies, Leeds, W Yorkshire (22.4 × 279 cm, 2020 – The Tree Register 2021) are typical of what it can achieve with time. Interestingly, it can perform well in areas with cool summers, such as North Yorkshire, where there is a good specimen (10.6 m × 155 cm, 2021) in an upland setting on carboniferous limestone near Skipton, at Parcevall Hall (The Tree Register 2021). It is rather commonly grown in Poland, where it is considered the hardiest magnolia, undamaged by severe winters and reaching above 21 m in height (Anisko & Czekalski 1991).

In North America it is commonly grown away from areas with very dry summers, making a fine shade tree and in its hardiest forms surviving colder winters than any other species. It stands out as being one magnolia which will tolerate calcareous soils in the Midwest. The current US champion, an immensely stout specimen in Stark Co. OH, was measured at 27.7 m × 785 cm in 2019 (American Forests 2021) although taller specimens have been recorded.

Magnolia acuminata is often used in North America as a roostock for grafting other magnolias. In Scandinavia, where a number of magnolias are at their limits of hardiness, a M. acuminata rootstock is thought to improves the scion’s cold hardiness.

Hybrids involving M. acuminata are a relatively modern phenomenon, largely driven by the quest for yellow, precocious flowering trees. The hardiness and variability of M. acuminata are important features for the breeder. Early work by Evamaria Sperber and others at the Brooklyn Botanic Garden’s Kitchawan Research Station, New York began in the 1950s. It led to the various M. × brooklynensis cultivars (M. acuminata × M. liliiflora) and hybrids between M. acuminata and M. denudata such as ‘Elizabeth’. Breeding work down these and other lines continues; very many cultivars have been named, and the quest is now on to identify the most gardenworthy of them.