Magnolia macrophylla Michx.

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Credits

Julian Sutton (2022)

Recommended citation
Sutton, J. (2022), 'Magnolia macrophylla' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/magnolia/magnolia-macrophylla/). Accessed 2022-07-01.

Genus

Common Names

  • Bigleaf Magnolia

Other taxa in genus

Glossary

section
(sect.) Subdivision of a genus.
key
(of fruit) Vernacular English term for winged samaras (as in e.g. Acer Fraxinus Ulmus)
pollen
Small grains that contain the male reproductive cells. Produced in the anther.
subspecies
(subsp.) Taxonomic rank for a group of organisms showing the principal characters of a species but with significant definable morphological differentiation. A subspecies occurs in populations that can occupy a distinct geographical range or habitat.

Credits

Julian Sutton (2022)

Recommended citation
Sutton, J. (2022), 'Magnolia macrophylla' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/magnolia/magnolia-macrophylla/). Accessed 2022-07-01.

Deciduous tree to 15(–32) m. Bark yellowish to grey, smooth. Branchlets and foliar buds silky-pubescent. Leaves crowded in terminal whorl-like clusters; stipules (9–)11–17 × 3–6.5 cm, glandular-hairy beneath. Leaf blade broadly elliptic to obovate-oblong, 50–110 × 15–30 cm, base truncate to deeply cordate or auriculate, apex acute to short-acuminate or obtuse; lower surface chalky white, sometimes pale green to glaucous, hairy; upper surface deep green, glabrous. Flowers in spring, solitary, fragrant, 35–40(–50) cm across; spathaceous bracts 2, outer bract rusty gray beneath, inner bract thinner, glabrous; tepals creamy white, glandular, innermost whorl purple-blotched at base, outermost segments strongly reflexed, greenish; stamens (300–)350–580, 12.5–24.5 mm; filaments white; carpels 50–80. Fruit globose-ovoid, 5–8 × 5–7 cm, reddish pink, ageing brown; follicles short-beaked, with silky hairs towards the tips. Seeds ± ovoid, 10–12 mm, pointed, aril orange-red. Flowering May in the wild, June–July (UK). Diploid 2n=38. (Meyer 1997).

Distribution  United States Southeast, absent from Florida and the Atlantic seaboard

Habitat Alluvial woods and sheltered valleys, piedmont; 150–300 m.

USDA Hardiness Zone 5-8

RHS Hardiness Rating H4

Conservation status Least concern (LC)

Potentially huge, banana-like leaves – the largest in the genus – and similarly gargantuan flowers make Magnolia macrophylla an alluring prospect for the garden, but it needs a sheltered, sunny site and hot summers for its full potential to be realized. The typical form is usually a small to medium sized tree in the wild, often multistemmed.

Two quite distinct varieties, var. ashei and the Mexican var. dealbata are also known (see below); they have been – and sometimes still are – considered subspecies, or species in their own right. Until recently, these were thought to be the only members of Section Macrophylla. However, a flurry of further Mexican species, all very local, were described in this Section between 2013 and 2021. These are: M. alejandrae García-Mor. & Iamonico, M. mixteca A.Vázquez & Domínguez-Yescas, M. nuevoleonensis A.Vázquez & Domínguez-Yescas, M. rzedowskiana A.Vázquez, Domínguez-Yescas & R.Pedraza, M. vovidesii A.Vázquez, Domínguez-Yescas & L.Carvajal, and M. zotictla A.Sánch.-Gonz., Gut.-Lozano & A.Vázquez (Vázquez-García et al. 2021 and references therein). This is in effect a dismantling of var. dealbata – and hence M. macrophylla as a whole – into more natural taxa. Still not well known, it remains to be seen whether those who treat ashei and dealbata as varieties of M. macrophylla will do the same with these new taxa. To help assess Mexican material of Section Macrophylla in cultivation, we include a key below.

William Bartram appears to have encountered Magnolia macrophylla in the southern Appalachians in the mid 1770s, recognizing it as distinct from M. fraseri. However it was André Michaux who first collected it around 1790 (Williams 1999), rather than in 1759 as often repeated (e.g. Bean 1981); he described and named it in his posthumous Flora Boreali-Americana (Michaux 1803). The tree was already well known to the Cherokee, who used the wood and made an infusion of bark to treat stomach ache and toothache (Moerman 2021). Introduced to Europe by 1800 (Bean 1981), it had flowered – perhaps with protection – in Empress Joséphine’s garden at the Malmaison near Paris by 1813 (Bonpland 1813) and in England by 1820 (Sims 1821).

Despite their size, the leaves have a rather flimsy, papery appearance; they are light green above and either grey-green or brownish beneath. A sheltered site is needed for them to look their best, wind damage making the tree look ‘bedraggled and crude’ (Jacobson 1996). In cool, maritime climates the leaves do not become so large, but may still reach 60 cm long in Britain.

The flowers can be even larger than those of Magnolia grandiflora, with creamy white tepals typically marked purple at the base – populations with unmarked flowers are known in Alabama and Mississippi (Treseder 1978). They are protandrous and remain open for two days, not closing between the male and female phases. Both beetles and bees are attracted to the flowers. Beetles may enter open or closed flowers, or even buds; they feed on nectar, pollen and flower parts, and are effective pollinators (Thien 1974). There are suggestions (summarized by Cleary & Adler 2020) that insects other than beetles are sometimes harmed or become lethargic when visiting the flowers. In areas with cooler summers, such as the British Isles, Bigleaf Magnolia does not flower prolifically.

Provided effective ripening of the wood takes place, M. macrophylla is hardy well beyond the American southeast; it has become naturalized in parts of New England (Moorhead et al. 2017). A sunny but sheltered site with rich, moisture retentive soil is the ideal, reflecting its native habitat. Its shallow roots can make underplanting difficult (Hetman 2019). Seedlings take 12–15 years to reach flowering size.

In the British Isles most records of large specimens are from the south and west, although the species certainly grows in colder central areas. Extremes of girth and height include a specimen in a private Dorset garden, significantly in a valley bottom (18 m × 132 cm, 2017) and at Mount Congreve, Co. Waterford, Ireland (16.8 m × 110 cm, 2002 – The Tree Register 2021). It suits milder parts of France, and is well represented in Belgian and Dutch collections (Plantcol 2021; Hortus Botanicus Amsterdam 2021).

The first record of cultivation in North America outside its native range is from Pennsylvania in 1800 (Jacobson 1996). It is now widely grown away from the coldest and driest areas, thriving in cities as climatically diverse as Boston, Cincinatti, St Louis, Wichita, San Francisco and Vancouver, although the finest specimens are in the South (Dirr 2009). The current US champion is a narrow crowned, single trunked specimen in Buncombe Co., NC measured at 20.4 m × 206 cm in 2021 (American Forests 2021).

Garden hybrids between the varieties, and also with M. sieboldii are known.

The following key to taxa within Section Macrophylla, following contemporary Mexican work, is slightly modified from Vázquez-García et al. (2021). All these taxa apart from M. macrophylla s.s. and M. ashei map onto M. macrophylla var. dealbata as used here.

Identification key

1aMature fruit broadly ovoid, broadly ellipsoid to subglobose2
1bMature fruit oblongoid, ovoid or ellipsoid4
2aLeaves 50–110 cm long; tepals 20–23 cm; gynoecium 4 cm long; stamens (300–)350–580; carpels (44–)50–80; growing at 150–300 m (SE USA)M. macrophylla s.s. (= var. macrophylla)
2bLeaves 25–35(–40) cm long3
3aTepals 10–11 cm long; carpels 30–40; growing at 1500–1700 m (Mexico: Nuevo León)M. nuevoleonensis
3bTepals 12–15 cm long, carpels 58–62; growing at 1800–220 m (Mexico: Oaxaca)M. mixteca
4aCarpels shortly (<0.7 cm) beaked5
4bCarpels prominently (1.0–1.5 cm) beaked6
5aMulti-trunked large shrub or small tree 8–10(–12) m; fruit cylindrical to ellipsoid; carpels 20–25(–50), shortly beaked; growing at <150 m (USA, Florida)M. ashei s.s. (= macrophylla var. ashei)
5bSingle-stemmed trees 8.0–25.0 m; fruit rhomboid-ovoid; carpels 50–65; growing at 800–1950 m (Mexico: San Luis Potosí, Querétaro & Hidalgo)M. rzedowskiana
6aCarpels 42–787
6bCarpels 80–1278
7aStamens 192–216, carpels 42–54 (Mexico: Tamaulipas)M. alejandrae
7bStamens 308–352, carpels 60–78 (Mexico: Veracruz)M. vovidesii
8aFruit dark green to yellow, young fruits glabrescent; stamens 1.3–1.8 cm; carpels acute to blunt, tip deciduous (Mexico: Oaxaca)M. dealbata s.s.
8bFruit pinkish/purplish to dark red, young fruit velvety; stamens 1.9–2.1 cm; carpels acuminate to caudate, tip sometimes persistent at dehiscence (Mexico: Hidalgo/Puebla border)M. zotictla

'Sara Gladney'

Pure white flowers, slightly earlier flowering; selected at the John James Audubon Foundation, Gloster Arboretum, Mississippi, by 1981.


var. ashei (Weatherby) D.L. Johnson

Common Names
Ashe's Magnolia

Synonyms
Magnolia ashei Weatherby
Magnolia macrophylla subsp. ashei (Weatherby) Spongberg

Differs from typical M. macrophylla in forming a smaller tree, to 12 m; in its more elongated fruits (cylindric to nearly ovoid, 2.5–6.5 cm long); in its smaller leaves (17–56 cm); and in having fewer stamens (170–350) and carpels (20–50). Also differs from var. dealbata in its smaller fruits and fewer carpels. The ranges of the three do not overlap. (Meyer 1997).

Distribution

  • United States – Florida Panhandle

RHS Hardiness Rating: H5

USDA Hardiness Zone: 6-9

This smaller variety is a rare plant in the wild. Ashe’s Magnolia is usually considered rather less hardy than the type, although Dirr (2009) reports it being grown near the Maine coast. As a wild plant in woodland understorey it grows in association with other horticulturally desirable trees and shrubs including as Ostrya virginiana, Stewartia malacodendron, Illicium floridanum, Kalmia latifolia and Aesculus pavia. Outer tepals typically, but not always, have a maroon basal blotch. It is notable for its seedlings flowering when still small, as little as 3 years old and 30 cm tall (Treseder 1978). Originally published as a full species, and still treated as such by some, the name commemorates the Southern forester, botanist and early conservationist William Ashe, who collected the type specimen.

In Europe it is much less widely grown than the type. Significant British specimens include plants at the Valley Gardens, Windsor Great Park (6 m × 38 cm, 2021) and the Sir Harold Hillier Gardens, Hampshire (4.2 m × 69 cm, 2009 –The Tree Register 2021). In Belgium it is recorded from Kalmthout and Bokrijk arboreta, and at Meise Botanic Garden (Plantcol 2021).

In North American cultivation Jacobson (1996) considered it extremely rare before the 1990s, but considered it much better suited to urban gardens and amenity plantings than its ‘enormous, clumsy peer’ var. macrophylla. The current American champion in Wakulla Co., FL measured 7 m × 71 cm in 2021 (American Forests 2021).


var. dealbata (Zucc.) D.L. Johnson

Common Names
Eleoxochitl

Synonyms
Magnolia dealbata Zucc.
Magnolia macrophylla subsp. dealbata (Zucc.) J.D. Tobe

Differs from typical M. macrophylla in that the mature carpels are oblong rather than ovoid or globose. It differs from var. ashei in that its fruits are 8–15 cm long (vs. 2.5–6.5 cm) and have >70 carpels (vs. <50). The ranges of the three do not overlap. (Tobe 1998).

Distribution

  • Mexico – Hidalgo, Oaxaca, Veracruz.

RHS Hardiness Rating: H4

USDA Hardiness Zone: 7-10

Taken here in the wide sense, including all Mexican plants of Section Macrophylla, this shares the splendid big leaves and creamy flowers of typical var. macrophylla, but has the additional advantages of being easier to grow and quicker to come into flower than its more northerly counterpart. It has therefore been recommended for gardens, at least in Cornwall (Hudson 2004), although it seems probable that the same qualities will be demonstrated elsewhere. Described as early as 1837, the specific epithet (from the Latin dealbatus, ‘whitened’ or ‘whitewashed’) refers to the glaucous underside of the leaves, which it shares with the type variety. Treseder (1978) makes a careful case for this being the first Magnolia illustrated by European science, by Francisco Hernandez during his 1570–7 expedition. Flowers and dried buds of this and other Mexican magnolias are used in traditional medicine, and the flowers gathered and sold for home decoration (Pfaffman 1975; Treseder 1978; Vázquez-García et al. 2021).

The physical differences between the varieties are slight, however, and it is not always easy to distinguish them on morphological characters alone (N. Macer, pers. comm. 2007). The leaves of var. dealbata are slightly more succulent than those of var. macrophylla and are somewhat glaucous below; they also persist on the trees longer in the autumn, especially where the climate is mild (S. Hogan, pers. comm. 2007). Trees approaching 10 m tall at Berkeley, CA only lose their leaves in colder weather, and have survived a freeze of –10.5 °C (S. Hogan, pers. comm. 2007). It has been suggested that the leaves of var. dealbata have stouter petioles and are more wind-resistant than those of var. macrophylla (M. Robinson, pers. comm. 2008), but a sheltered site is still recommended.

It was first introduced to cultivation through a Harold Hillier collection of 1979. Examples from that collection include the vigorous British champion at Chyverton, Cornwall (15 m × 85 cm, 2016 – The Tree Register 2021)). Some other older British trees may derive from a gathering of six seeds by James Russell made at around 1450 m in Veracruz, 1983 (JR 413), raised by him at Castle Howard, Yorkshire. Russell’s field-notes (JR 413) record that he saw about 100 trees, only four of them fruiting, of upright, almost fastigiate habit, to about 18 m high with deciduous leaves 30–40 × 17–20 cm, fresh green above, silvery green beneath, in the company of oaks, liquidambar and Clethra xalapensis (J. Grimshaw pers. comm.). One further older collection by G. Pattison (s.n.) from Veracruz, 1985, gave rise to the Berkeley trees mentioned above.

It seems important to understand how cultivated material relates to the many new Mexican taxa outlined in the key above. Much direct observation by those that grow them is needed. It is worth noting that M. dealbata in the narrowest sense is endemic to Oaxaca.


'Whopper'

Large flowers with 3 sepaloid tepals and 12 petaloid tepals measuring up to 20 × 13 cm, with basal spots forming a purple ring. Selected 1970s by Joe McDaniel, Urbana, IL. Starred as worthwhile by Philippe de Spoelberch, Belgium (pers. comm. 2021).