Magnolia L.

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Article from Bean's Trees and Shrubs Hardy in the British Isles

Article from New Trees, Ross Bayton & John Grimshaw

Family

  • Magnoliaceae

Common Names

  • Magnolias

Synonyms

  • Alcimandra Dandy
  • Aromadendron Blume
  • Dugandiodendron Lozano
  • Elmerrillia Dandy
  • Houpoëa N.H. Xia & C.Y. Wu
  • Kmeria Dandy
  • Manglietia Blume
  • Manglietiastrum Y.W. Law
  • Michelia L.
  • Pachylarnax Dandy
  • Parakmeria Hu & W.C. Cheng
  • Paramanglietia Hu & W.C. Cheng
  • Paramichelia Hu
  • Talauma Juss.
  • Tsoongiodendron Chun
  • Woonyoungia Y.W. Law
  • Yulania Spach

Glossary

Critically Endangered
IUCN Red List conservation category: ‘facing an extremely high risk of extinction in the wild’.
gynoecium
The female sex organs in a flower (e.g. carpels).
IUCN
World Conservation Union (formerly the International Union for the Conservation of Nature).
perianth
Calyx and corolla. Term used especially when petals and sepals are not easily distinguished from each other.
section
(sect.) Subdivision of a genus.
Vulnerable
IUCN Red List conservation category: ‘facing a high risk of extinction in the wild’.
adnate
Fused with a different part by having grown together. (Cf. connate.)
alternate
Attached singly along the axis not in pairs or whorls.
auriculate
With one or more auricles.
bisexual
See hermaphrodite.
calyx
(pl. calyces) Outer whorl of the perianth. Composed of several sepals.
carpel
Female reproductive organ of a flower. Composed of ovary style and stigma. Typically several carpels are fused together in each flower (syncarpous). The number of them can be of taxonomic significance; it can often be assessed by counting the stigma branches or the chambers in the fruit.
conduplicate
(of leaves) Folded once lengthwise.
cordate
Heart-shaped (i.e. with two equal lobes at the base).
corolla
The inner whorl of the perianth. Composed of free or united petals often showy.
Critically Endangered
IUCN Red List conservation category: ‘facing an extremely high risk of extinction in the wild’.
ellipsoid
An elliptic solid.
entire
With an unbroken margin.
family
A group of genera more closely related to each other than to genera in other families. Names of families are identified by the suffix ‘-aceae’ (e.g. Myrtaceae) with a few traditional exceptions (e.g. Leguminosae).
glabrous
Lacking hairs smooth. glabrescent Becoming hairless.
hybrid
Plant originating from the cross-fertilisation of genetically distinct individuals (e.g. two species or two subspecies).
key
(of fruit) Vernacular English term for winged samaras (as in e.g. Acer Fraxinus Ulmus)
morphology
The visible form of an organism.
ovoid
Egg-shaped solid.
perianth
Calyx and corolla. Term used especially when petals and sepals are not easily distinguished from each other.
petiole
Leaf stalk.
precocious
The production of flowers/inflorescences prior to leaf emergence. (Cf. coetaneous serotinous.)
section
(sect.) Subdivision of a genus.
sepal
Single segment of the calyx. Protects the flower in bud.
sessile
Lacking a stem or stalk.
simple
(of a leaf) Unlobed or undivided.
taxonomy
Classification usually in a biological sense.
vernation
Arrangement of a leaf in its bud.
whorl
Arrangement of three or more organs (leaves flowers) around a central axis. whorled Arranged in a whorl.

References

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Credits

Article from Bean's Trees and Shrubs Hardy in the British Isles

Article from New Trees, Ross Bayton & John Grimshaw

Magnolias are evergreen or deciduous trees or shrubs with alternate, entire, pinninerved leaves. Stipules are present and initially enclose the terminal bud, later falling leaving a scar; they are often called ‘perules’ when covering an overwintering flower bud, and are often attractively hairy. Magnolia flowers are solitary, hermaphrodite or rarely unisexual; they are terminal on long shoots or on short axillary shoots (brachy-blasts). The floral parts are arranged in turn along an elongated receptacle; the perianth is composed of six or more distinct petal-like tepals, and occasionally the outer three tepals may differ from the inner ones; stamens are numerous, spirally arranged and flattened and the anther is poorly differentiated from the filament. The pistillate part of the flower (gynoecium) may be sessile or stipitate (with a stalk). Carpels are numerous (rarely solitary) and spirally arranged; they may be free (apocarpous) or fused (syncarpous). Fruiting carpels (follicles) are usually dehiscent, and each produces one or more large seeds. The carpels may be fleshy, and can fuse together to form a berry-like fruit (the term ‘fruit’ will be used here to refer to the aggregate of follicles, whether fused together or not). After dehiscence, the follicles often become woody and persist on the tree. The seeds each have a red or orange fleshy aril and are often pendulous, hanging out from the carpel on a slender thread (Chen & Nooteboom 1993).

Magnolia in its traditional interpretation is well known to gardeners and collectors, and numerous species were described by Bean (1981a) and Krüssmann (1985a). In recent years, however, there have been major changes in the taxonomy of the Magnoliaceae, largely as the result of the publication of several phylogenetic studies (for example, Azuma et al. 1999, 2000a, Ueda et al. 2000, Azuma et al. 2001, Kim et al. 2001, Li & Conran 2003) demonstrating the close relationship of all groups within the subfamily Magnolioideae. This DNA-based work has been confirmed by recent critical interpretations of magnolioid morphology (Figlar 2006). The outcome of these changes is that the Magnoliaceae family now comprises only two genera, Liriodendron L. and Magnolia; all other genera (including Michelia and Manglietia, and the others indicated as generic synonyms above) have been subsumed into Magnolia to preserve monophyly (Chen & Nooteboom 1993, Figlar 2000, Nooteboom 2000, Figlar & Nooteboom 2004, Kumar 2006). An accessible exposition of the reasons for change has been given by Magnolia expert Richard B. (Dick) Figlar (Figlar 2006), who has also kindly advised us for this account. The crux of the matter is that to recognise separate genera (for example, Michelia, Manglietia), as some traditionalists would like to do, logically requires the dismemberment of Magnolia itself – an act that would serve neither phylogeny nor taxonomic stability. (Yulania ×soulangeana anyone?)

In consequence, Magnolia now contains three subgenera (Magnolia, Yulania, Gynopodium), twelve sections and thirteen subsections, each clearly supported by both DNA and morphological characters. A complete summary of Magnolia classification is provided by Figlar (Figlar 2006). The new classification has been adopted by the Magnolia Society International, and 224 species of Magnolia are now recognised (Figlar 2005a). About four-fifths of these occur in eastern Asia, from the Himalaya east to Japan and south to New Guinea. The remaining fifth occur in eastern North America, Central America and northern and central South America. Many of the tropical species are not known in cultivation in our area. A summary of the infrageneric classification of Magnolia and the key characters defining each group, for the species covered in this book, is presented in the table opposite.

The current adherence of Chinese botanists and the recently published Flora of China (Xia et al. 2008) to a fragmented view of Magnoliaceae means that two parallel taxonomies are in use, so the alternative names in Michelia, Manglietia, etc. are likely to persist in both literature and nurseries for many years to come. The lead given by the Magnolia Society in adopting the broad view of Magnolia is to be applauded and should be followed in horticulture. The online Kew World Checklist of Magnoliaceae and the IUCN Red List of Magnoliaceae (Cicuzza et al. 2007) both follow the unified Magnolia approach.

MAGNOLIA L.

A guide to the infrageneric classification of Magnolia species covered in New Trees

Subgenus Magnolia

Leaf vernation conduplicate (folded in half)

Flowers terminal on long shoots

Mid- to late-flowering season

Gynoecium sessile

Fruit ovoid-ellipsoid, with fused carpels until dehiscence

Section Magnolia (e.g. M. grandiflora, M. virginiana)

Leaves evergreen, sub-evergreen or deciduous

Stipules adnate to the petiole base (or adnate to most of petiole, in M. virginiana)

Ovules two per carpel

Section Manglietia (e.g. M. insignis)

Leaves evergreen (not M. decidua!)

Early-season leaves sometimes produced in a false whorl

Ovules four or more per carpel

Section Macrophylla (e.g. M. macrophylla)

Leaves deciduous

Leaf bases cordate to auriculate

Tepals with purple spot at base of upper side

Subgenus Yulania

Leaf vernation conduplicate

Stipules adnate to base of petiole

Flowers terminal and/or on brachyblasts

Flowering precocious (before new leaves produced)

Gynoecium sessile or stalked

Fruit more or less cylindrical, carpels fused or not

Section Yulania (e.g. M. campbellii, M. denudata)

Leaves deciduous

Flowers terminal or occasionally on brachyblasts

Carpels fused

Ovules approx. two per carpel

Section Michelia (e.g. M. figo, M. doltsopa)

Leaves evergreen

Flowers on brachyblasts

Carpels not fused

Ovules two to six per carpel

Subgenus Gynopodium

Leaf vernation open (not folded)

Stipules free

Plants entirely glabrous

Gynoecium stalked (rarely sessile)

Fruit more or less ovoid-ellipsoid, with fused carpels until dehiscence

Section Gynopodium (e.g. M. nitida)

Gynoecium stalked

Carpels split via the upper valve

Ovules two (to four) per carpel

Section Manglietiastrum (e.g. M. sinica)

Gynoecium sessile

Carpels split via the lower valve

Ovules three to eight per carpel

For a complete summary see Figlar (2006).

Magnolia has long been one of the most universally popular genera of flowering trees in gardens around the world, contributing a major part of the spring floral display. Most of these early, precocious-blooming plants belong to section Yulania, a relatively small group of the genus overall, although under the influence of cultivation and the work of hybridisers the number of named taxa in the group is now vast and everexpanding. Breeding work is adding genes from other sections to this pool, but the pink and white flowers of section Yulania are the most familiar face of Magnolia (discussed and explored in a range of horticultural literature). Members of other sections of the ‘traditional’ genus Magnolia are generally much less familiar, with the exception of M. grandiflora (section Magnolia), unchallenged as the finest flowering evergreen tree for temperate gardens. Other summer-flowering species have tended to be more plants for the enthusiast rather than the general gardener.

Beyond the narrow circumscription of Magnolia the sections Michelia and Manglietia have been represented in cultivation by a few noble old trees in the mildest parts of Cornwall, and in pockets of the United States. The beauty of the old trees of M. doltsopa and M. floribunda at Caerhays Castle should have sparked a wider interest earlier, but it is only within the past 10–15 years that Asian evergreen magnolias have really come to the attention of horticulture (Wharton 2007, Figlar 2008, Robinson et al. 2008). The wave of excitement they have caused started in western North America, where introductions by Piroche Plants and others, and enthusiastic promotion by horticulturists such as Sean Hogan, have led to them becoming very much a part of the landscape in the Pacific Northwest. This interest has spread in recent years to Europe, and nurseries are now offering a wide range of these trees. Many are too new in cultivation to allow much to be said of their long-term performance in European conditions, but for warmer parts of maritime Europe, in a time of rising temperatures, they hold immense promise. Tom Hudson (2004) has summed up the position admirably: ‘Michelia are exceptionally ornamental plants in habit and flower, and many an unexciting old magnolia hybrid should be tidied up by an adventurous gardener, to make way for a Michelia.’ Hybridisation is in progress in Australasia and it is probable that a wave of new hybrid cultivars will appear before long (Robinson et al. 2008).

Introductions from China and Vietnam continue apace and it is probable that many collections of new taxa, or of ‘familiar’ species from new provenances (such as dark red-flowered forms of Magnolia delavayi and M. insignis, already in cultivation), will be entering horticulture in the next few years. Identifications will often follow or need revision after trees have flowered. Magnolias of China (Liu et al. 2004) gives a very tempting view of the richness of the Magnoliaceae in China, and shows that although we have had a chance to grow many taxa, there is a huge diversity still to be explored in horticulture. For example, only four deciduous ‘traditional’ magnolias of section Yulania are described in the accounts that follow, but to judge from the illustrations in Magnolias of China there are several more taxa with considerable horticultural potential awaiting introduction to Western gardens; very many evergreen species in other sections remain to be explored as well. With the exception of M. tamaulipana, the numerous species of Magnolia from Latin America are also almost unknown in cultivation, but a handful are being grown at Berkeley, including M. guatemalensis Donn. Sm., M. schiedeana Schltl., and M. sharpii V.V. Miranda.

The critical state of many Magnolia populations, as a result of deforestation and habitat degradation, has been highlighted by the publication of The Red List of Magnoliaceae (Cicuzza et al. 2007). This provides the stark warning that 131 of the 245 members of Magnoliaceae – over half – are threatened with extinction in the wild, and that the ‘safety’ of the others should not be taken for granted. Ninety-four species have not been evaluated at all, including many from areas well known to be under severe pressure from habitat destruction and degradation. The revised conservation status of each species is given in the descriptions that follow. Conservation orchards of magnolias have been established in China, and it is hoped that these will provide a source of material for future reintroductions. Cicuzza et al. (2007) report that nursery-grown seedlings of M. sinica are already being planted in native forests to boost numbers of this critically endangered tree. However, seed from these sources should be treated with some caution, as hybridisation is facilitated by the close proximity of different species.

Magnolias are in general relatively easy to raise from seed, with fresh seed giving the best results and fastest germination times (almost immediate for evergreen species sown from the newly dehisced fruit: Hogan 2008). Propagation by cuttings under conditions of high humidity and bottom heat, with a rooting hormone, is also usually not difficult, but is best achieved with vigorous non-flowering shoots. Material from older trees becomes less susceptible to the propagator’s skills. For michelias in particular, Sean Hogan recommends the use of shoots from the trunk or the base of the plant. Grafting onto a stock of a section Yulania magnolia works very well for members of section Manglietia, at least, and could perhaps be tried for other sections.

Magnolias can take many years to flower from seed (vegetatively propagated plants are usually much quicker to flower), so the raiser must be patient. Many of the more recently introduced Asian evergreen species described here have yet to flower ‘in captivity’ and their blooming is eagerly awaited. In the meantime, however, they are often extremely handsome foliage plants. As always, the ecology of the species in the wild should be considered. Many species of evergreen Magnolia germinate and spend their juvenile period in the shade of the forest understorey, gradually growing in low light conditions until a gap opens and they can rise to become emergents or canopy trees flowering in the sunlight. Many are indeed huge timber trees, a world away from the dainty magnolias of suburbia. Young trees therefore require a sheltered position where they are not scorched by the hottest afternoon sun – although in northern gardens especially they need all the heat they can get if they are to grow and flower successfully. They also enjoy ample moisture during the growing season, and should not be allowed to become dry for more than a very short period. In most cases it would seem that the evergreens prefer a mildly acidic soil, but a few, such as M. laevifolia, seem to be happy in soil with a higher pH. More experimentation is needed to ascertain the lime tolerance of most of the species described here.

Hogan (2008) repeatedly stresses the need for an adequate supply of nitrates and iron, and sometimes magnesium, for the successful growth of Asian evergreen magnolias. Without this they soon become yellowish and less vigorous – effects that are particularly significant in cooler climates where such warmth-loving plants can be slow to start growing in spring. In the accounts that follow, notes on flowering time in the botanical descriptions refer to trees in the wild; times may differ significantly in cultivation. For example, members of section Yulania often flower earlier in cultivation than in their native habitat.

With such an enthusiastic following there are many great Magnolia collections around the world, and these and their growing conditions are detailed by Gardiner (2000). Fewer gardens have a good range of the Asian evergreens but there is a centre of diversity of these around Portland, Oregon, especially in the collection gathered by Sean Hogan of Cistus Nursery. Quarryhill Botanical Garden and the David C. Lam Asian Garden at the University of British Columbia’s Botanical Garden also have good and expanding collections in western North America. In the southeastern United States michelias are popular, thriving in high heat and humidity, and collections are being developed in several locations including the garden of the University of Florida, the North Florida Research and Education Center, Quincy, Florida, and the South Carolina Botanical Garden at Clemson, South Carolina – and in the same state there is Dick Figlar’s own collection at Magnolian Grove Arboretum, Pickens. In our area there are useful selections at the JC Raulston Arboretum and in other gardens in the North Carolina piedmont; also at the US National Arboretum and at the Norfolk Botanical Garden, Norfolk, Virginia. Further north, however, they are more or less unknown. The more recent advent of these trees in Europe means that while many are growing them and numerous species are available commercially, few gardens have collections with sizable trees. An exception is Tregrehan, where they flourish in the mild, moist conditions.

Several further species are cultivated in American collections outside our area and are likely to be tried further north. They include the Endangered Chinese M. lacei (W.W. Sm.) Figlar and the Vulnerable M. odora (Chun) Figlar from southern China and northern Vietnam (both in section Michelia). The latter is also in cultivation in Europe, but its hardiness is as yet unknown.

Bean’s Trees and Shrubs

Magnolia

A genus of deciduous or evergreen trees and shrubs named by Linnaeus in honour of Pierre Magnol, a professor of botany and medicine at Montpelier, who died in 1715.

The genus is most numerously represented in E. and S.E. Asia, as far south-east as Java. A little over one-quarter of the species are natives of the New World, from the N.E. United States (one species just extending into Canada) to northern South America. More than half the species are tropical; of the temperate species, almost every one has been introduced to Britain.

In one respect magnolias are the most splendid of all hardy trees, for in the size of their individual flowers they are easily first; the evergreen species, too, have some of the largest leaves of all evergreen trees hardy with us. The leaves are alternate, simple and entire, with stipules that are free from the petiole in some species, in other adnate to it. Flowers bisexual, produced singly at the end of a shoot; peduncles with one or more spathe-like bracts. Perianth of six or nine (occasionally more) segments known as ‘tepals’, arranged in whorls. In some species the tepals of the outer whorl are small and sepal-like; in describing these species it is usual to term the outer whorl a calyx and the inner segments petals, but in no species of magnolia is there a complete differentiation of the perianth into calyx and corolla. The stamens are numerous, spirally arranged to the lower part of structure (the torus), the upper part of which bears numerous free carpels, also spirally arranged. In the fruiting stage the torus is much enlarged and the carpels split on their outer side to release one or two red, scarlet, or orange seeds, each of which is attached to the carpel by a silk-like thread.

In most of the species, the bark when crushed emits a pleasant aromatic odour, and some of the American species, as well as the Chinese M. officinalis, have medicinal properties.

Perhaps no group of exotic trees gives more distinction to a garden than a comprehensive collection of magnolias. There is not one that is not worthy of cultivation, the early-flowering or Yulan section being especially noteworthy for the brilliant effect they produce in spring.

The only difficulty experienced in cultivating these trees is in establishing some of them after transplanting. The roots are thick and fleshy, and apt to decay if disturbed and lacerated when the trees themselves are at rest. Any planting, therefore, which involves root injury should be done when active growth has commenced, so that the wounds may heal and new roots be formed immediately. May is a suitable month. The more delicate-rooted species like M. sieboldii and stellata like a proportion of peat in the soil, more especially when they are young. All of them like abundant moisture and where the soil is shallow and poor, holes 18 in. deep and 2 to 4 yards in diameter should be prepared by mixing good loam, and if possible one-fourth peat and decayed leaves with the ordinary soil. The dimensions of the prepared ground should, of course, be proportionate to the vigour of the species. In most gardens the ordinary soil, well trenched and improved by adding decayed leaves, will be found suitable, but for such delightful plants as these a little extra labour and expense at the outset will be repaid.

Magnolias are propagated by seed, layering, and grafting. For the pure species, seeds no doubt are preferable, but their production in this country is uncertain, and it has to be remembered that being of an oily nature they retain their vitality but a short time if kept dry. It is advisable to sow them singly in small pots of light soil under glass. Seeds of magnolias are sometimes very long in germinating. A batch of about two hundred seeds of M. wilsonii, ripened at Kew some years ago, remained dormant after sowing for over two years, then germinated simultaneously with scarcely a failure.

Layering is a very useful means of increase and was much used by Messrs Veitch at their Coombe Wood nursery, where there were many old stools, each of which had produced hundreds of young plants. Air-layering is a possibility in gardens, when only a few plants are needed. Where layering is inconvenient or impossible, grafting will have to be employed; M. acuminata can be used as the stock for the stronger growing kinds, and M. kobus for M. stellata, M. × loebneri and other smaller growing species and hybrids. But grafting should be the last resort. Some magnolias can be propagated by cuttings, notably M. grandiflora and delavayi, both evergreen, M. stellata, salicifolia, and kobus (and their hybrids); some success has also been attained in propagating M. × soulangiana by this means.

With regard to the attitude of magnolias towards chalky soils, the late Sir Frederick Stern wrote, in his book on the garden at Highdown, near Worthing: ‘Few magnolias do well on this hot dry soil. The American magnolias, like so many of the American plants, will not tolerate lime. Some of the Asiatic species do not mind lime, such as M. delavayi, M. kobus, M. sinensis, M. wilsonii and M × highdownensis. None of the other Asiatic magnolias have ever succeeded here; perhaps the ground and the position of the garden facing south is too hot and dry for them’ (A Chalk Garden (1960), p. 44). But a wide range of magnolias is grown by Lord Rosse at Birr Castle in central Ireland, where the soil is alkaline but not chalky as it is at Highdown and is also moister (Journ. R.H.S., Vol. 78 (1953), pp. 102-104).

The standard work on the magnolias of temperate E. Asia is: G. H. Johnstone, Asiatic Magnolias in Cultivation (1955), with fourteen coloured plates, twenty half-tone figures, and one map. An older work on the whole genus, still of interest, is: J. G. Millais, Magnolias (1927). See also: Camellias and Magnolias, R.H.S. Conference Report (1950). Information on new cultivars and hybrids not included here will be found in Bud-grafted Magnolias, published periodically by Messrs. Treseder of Truro; and in the Manual of Messrs Hillier of Winchester. An account of magnolias at Kew, by S. A. Pearce, was published in Journ. R.H.S., Vol. 84 (1959), pp. 418-426; and of tree magnolias in Windsor Great Park, by T. H. Findlay, in Journ. R.H.S., Vol. 77 (1952), pp. 43-46, and Vol. 88 (1963), pp. 461-463.

From the Supplement (Vol.V)

Recent Literature

Grootendorst, H. J. – ‘Magnolia’s en Nederland’, Dendroflora No. 18, pp. 16-40(1981).

Spongberg, Stephen A. – ‘Magnoliaceae hardy in temperate North America’, Journ. Am. Arb., Vol. 57, pp. 254-306 (1976).

[ – – ] ‘Some old and new interspecific magnolia hybrids’, Arnoldia, Vol. 36, pp. 129-45(1976).

Treseder, Neil G. – Magnolias. London, 1978. An indispensable work by a leading authority, with many line-drawings by Marjorie Blarney and forty-eight colour plates, nine from paintings by the same artist.

[ – – ] The Book of Magnolias. London, 1981. Thirty colour plates from paintings by Marjorie Blarney.

For a classification of the genus by the late J. E. Dandy of the British Museum (Natural History), see Neil Treseder’s Magnolias, pp. 25-36. This is essentially the same as the classification by the same authority published in Camellias and Magnolias (an account of the conference of 1950, published by the Royal Horticultural Society). The main nomenclatural changes made by Mr Dandy are that sect. Magnoliastrum (p. 69) is now sect. Magnolia and subgenus Pleurochasma becomes subgenus Yulania.

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