USDA Hardiness Zone 5-8
RHS Hardiness Rating H6
This name covers all hybrids between M. obovata and M. sieboldii, including backcrosses to either parent, as well as F2 and subsequent generations of seedlings, so long as no other species becomes involved. Known only from gardens, they make large deciduous shrubs or small, bushy trees and are primarily grown for their fragrant flowers. Until the 1970s the slightly later synonym M. × watsonii was in general use.
Several very similar clones appear to exist (Treseder 1978); not all have cultivar names, and the original descriptions of M. × wieseneri and M. × watsonii were probably based on different clones (Clarke 1988). The rather leathery leaves are obovate, about 20 × 10 cm, bright green above with deeply impressed yellowish veins, glaucous and slightly hairy beneath; they tend to be clustered towards the shoot tips in false whorls. Flowers appear after the new leaves, rather sporadically from May to June in southern England; they are upward facing, initially cup-shaped but after a few days splaying open less attractively to 15–20 cm across. They have about nine white tepals and an eyecatching boss of red stamens. Their scent is perhaps the biggest attraction; variously described as ethereal, medicinal, spicy, aromatic, and pineapple-like (Gardiner 2000), it can be ‘almost overpowering’ (Edwards & Marshall 2019). Often confused with M. sieboldii, it is readily distinguished by its shorter-stalked, larger, upright flowers, and by the larger, more leathery leaves, with ten to fifteen pairs of veins (Bean 1981). Not a common plant, good specimens exist on both sandy and clay soils in Britain, although waterlogging is undesirable. Some particularly attractive examples at Nymans, W Sussex, are round-headed trees, one of them measured at 9 m × 126 cm in 2016 (The Tree Register 2022). An early reputation for being slow to establish may have been based only on poorly grafted specimens.
M. × wieseneri has been grown for many centuries in the Kyoto area of Japan; it may have originated in gardens there or in China (Smithers 1984). It reached Europe from Japanese cultivation in 1889, displayed at both the Japanese Court stand at the Paris Exposition and on a nurseryman’s stand at another Paris exhibition; both M. × wieseneri and the synonym M. × watsonii were described from these introductions, probably not from a single clone (Treseder 1978). Carrière’s epithet commemorates a Monsieur Wiesener of Fontenay-aux-Roses, who purchased the type plant at the show.
Such a lovely plant deserves wider cultivation.
Fast growing upright small to medium tree, single-stemmed with very symmetrical branching pattern; leaves very large, to 43 × 17 cm. Floriferous, with proven hardiness in Scandinavia. From open-pollinated seed of M. sieboldii at Gothenburg Botanic Garden, Sweden, raised by Olav Kalleberg, Norway; selected 1995.
This chance seedling from M. × wieseneri, probably a backcross with M. obovata as the pollen parent, belongs here if this surmise is correct. It has larger leaves and flowers (just as powerfully scented), and tends to make an upright medium tree. It originated in Sir Peter Smithers’ garden at Vico Morcote,Switzerland, before 1996. William Watson, a 19th century Assistant Curator at Kew, was originally commemorated by M. × watsonii.