Abeliophyllum distichum Nakai

Abeliophyllum distichum is valued for its very early flowers, appearing from February to April in the northern hemisphere depending on the severity of the winter. The thin stems can be wreathed in fragrant flowers for much of their length and when seen like this it is very beautiful, but if the show is sparser it can be quite underwhelming. For best effect it should have a dark background of evergreen plants (Dirr 2009), but in the UK at least it is often grown against a wall for both the support and extra warmth in summer and the flowers do not necessarily show well. Summer heat seems to be important for best growth and most reliable flowering: it flourishes through much of North America and continental Europe, enjoying hot summers but also surviving intense cold in areas such as Dresden (Kammemeyer 1972) and Minnesota where the flower buds are less prone to damage than those of Forsythia × intermedia (Dirr 2009), though frost can damage open flowers. Out of flower it is unremarkable, forming heaps of thin stems if unsupported, or a loose framework of stems if grown against a wall. It can have attractive autumn colour in yellow and soft orange tones. It is notable that Kim and Maunder (1998) undertook their field census of wild populations during the flowering season when the plants were clearly visible and making “a spectacular show against the russets and yellows of the previous season’s oak litter.” Flower colour is usually white, opening from dark buds and sometimes retaining a touch of pink at the corolla base. The name f. albiflorum Nakai is superfluous if white is taken as the colour of the type specimen (although this is not specified): such plants should be treated as f. distichum. Plants with creamy-white flowers have been named f. eburneum T. Lee but are not known in cultivation. More significant are pink-flowered variants (see f. lilacinum below), and some variation in flower size has been noted in wild populations (Kim & Maunder 1998). A variant that has been named f. viridicalycinum T. Lee suggests that the typical dark pigmentation of the calyx may sometimes be absent, but this form is not present in cultivation. The scent suggests almond blossom, and is more intense if brought into a warm room. Sir Peter Smithers (1995), a connoisseur of floral fragrance, placed it in ‘the upper second class.’ Although often called “White Forsythia” this is a rather misleading name, as the flowers are a fraction of the size of any Forsythia, though of the same shape: one imagines it was a nursery invention to link a novelty with a familiar plant.

If left unpruned and untrained plants form a low heaping shrub up to 1.5 × 1.5 m or thereabouts, but if trained on a wall they can exceed 2 m in height (Bean 1976). Some literature describes it as suckering but it is possible that this is a misidentification for naturally produced layers. Rejuvenation pruning may be desirable periodically, and should stimulate the production of long new shoots which will bear prolific flowers a year or two later, especially as they continue to be produced from old wood. It is important to stress that in areas with cool summers it needs as much warmth as it can get to grow and flower well. Propagation is by semi-ripe cuttings in summer, or by layering the stems (Bean 1976); it transplants easily at any age, and is not fussy about pH, though preferring well-drained soil (Dirr 2009).

Abeliophyllum distichum was discovered for science in upland central Korea by Takenoshin Nakai and described in 1919 (Korea was then occupied by Japan). As Director of the Tokyo Botanic Garden, Nakai sent living plants of a white-flowered clone to Kew in 1932 (Cotton 1948), but it was first introduced to western gardens through seed sent to the Arnold Arboretum by T. Ishidoya in 1924 (Wilson 1928). Some direct propagations from these original plants persist in cultivation there and the Arnold Arboretum database confirms that they were received as wild-collected seed: among them is a plant identified by the arboretum as ‘Roseum’ (see below). A specimen from the Arnold was sent to Lord Aberconway at Bodnant ‘about the same time’ as Nakai sent plants to Kew (Cotton 1948). In 1939 Lord Aberconway donated plants of this clone to Kew: one of these (accession 1939–31007) is still thriving against the wall in what is now known as the Salvia Border (T. Freeth pers. comm. from Kew records). Material was shown by Lord Aberconway to the Royal Horticultural Society in 1936 and 1937, receiving an Award of Merit in the latter year: a First Class Certificate followed in 1944 for sprays shown by the nurseryman J. Coutts of Woking. Its first appearance in commerce seems to be an offering by W.J. Marchant, Keeper’s Hill Nursery, Dorset, UK, in 1937 (Kim & Maunder 1998). The catalogue entry says it is “destined to become a favourite on account of its early flowering season” (Marchant 1937). It is assumed that Lord Aberconway distributed plants of his clone to other gardens and nurseries, as well as Kew.

Its rarity and restricted range as a wild plant was noted early on, and it has long been regarded as being of conservation concern (Cotton 1948; Kim & Maunder 1998; Lee et al. 2022). Kim and Maunder noted that it had only been recorded at seven localities in South Korea, with a few old Japanese records from North Korea. Since then the species has been found at new sites, so the total number of locations in South Korea is now 11 (Lee et al. 2022, where a map is available). All are widely spaced, with the closest pair in the central region of its range being 6 km apart, while others in the same region are up to 40 km apart. At least one of the sites in South Korea has been lost, and the population at another was compromised by the building of a dam, though suckers were relocated (Kim & Maunder 1998; Lee et al. 2022). Kim and Maunder’s conclusion that active conservation management was needed has been reinforced by the later work of Lee et al., whose genetic analyis has confirmed that there is little gene flow between populations, though most show reasonable heterogeneity within them. Some sites have the South Korean designation of Natural Monument to protect this endangered endemic (Lee et al. 2022).

An important factor in the low levels of inbreeding found in wild Abeliophyllum populations is the heterostylous flowers. As in the more familiar case of Primula, the flowers may be either thrum-eyed, with the stigma shorter than the anthers, or pin-eyed, where it is longer. Thrum × thrum, or pin × pin, will result in almost no seed being set: the cross must be thrum × pin (Lee et al. 2022). It seems certain that the vast majority of cultivated plants of Abeliophyllum are of very limited diversity, though Kim and Maunder (1998) report on some collections (mostly in Asia) with a greater diversity of accessions. A scrutiny of images available online through Google in January 2024 confirms that the vast majority of commercially offered plants are white-flowered and thrum-eyed (as are all images of pink-flowered plants) and match the illustration of the Kew specimens from Nakai (by Stella Ross-Craig in Cotton 1948); there are just a couple of images of pin-eyed plants, one of unknown origin shared by the British seed companies Suttons and Thompson & Morgan, and one on the Arnold Arboretum site (also available here, see below) showing a plant obtained from White Flower Farm, Connecticut, in 1987 (though not recently located at the Arnold, according to its database in January 2024). So it would seem that both are in cultivation in North America, though the pin-eyed clone is clearly rare, but anyone wishing to see the fruits will need to have both. Wilson’s (1928) comparison of the fruit to that of an elm has been widely repeated. For effective seed set it is probable that plants should be grown under cover and hand-pollinated. It would be very interesting to know more about the frequency of the two floral morphologies in cultivation: please send observations to editor@treesandshrubsonline.org.

Extensive observation in person and by proxy during the early months of 2024 have led the author to the conclusion that only one white-flowered clone, and only one pink-flowered clone, both thrum-eyed, are in cultivation in western Europe. Since they are both thrum-eyed it is safe to assume that no seed is ever set in cultivation, and this also applies in North America where thrum-eyed plants, white and pink, are in the vast majority. The European white-flowered plant seems to be the clone sent by the Arnold Arboretum to Lord Aberconway at Bodnant, with material later donated to Kew where the original plant can still be observed. Whether this clone remains in cultivation at the Arnold Arboretum or elsewhere in North America is unknown. The Kew plant was portrayed by Stella Ross-Craig in Curtis’s Botanical Magazine in 1948. As noted there (Cotton 1948), it has dark calyx lobes, and opens a very pale pink from pink-tinged buds but soon fades to white, though a trace of pink may be discernible on the outside of the corolla even in mature flowers. This plant should be given a cultivar name: ‘Bodnant’ is proposed. It is the ubiquitous Abeliophyllum distichum of commerce in western Europe.

The narrowness of the genepool – two reproductively incompatible clones in Western European gardens (and probably not many more in North America) – is a concern for a critically endangered plant. It is possible that a greater diversity of clones is in cultivation in eastern Europe, through former communist links with North Korea. Tom Christian (pers. comm. 2024) observed and photographed fruits at Szarvasi Arboretum, Hungary, in mid-September 2019, which implies that both floral morphologies are cultivated there. Unfortunately it has not been possible to find out more information. In late 2024 Eike Jablonski from Luxembourg was given Abeliophyllum seed while visiting South Korea (pers. comm. 2024), giving hopes of greater genetic diversity in cultivation in the future.

Thanks are due to the following for correspondence, insights and observations on Abeliophyllum distichum in cultivation during the early part of 2024: Jack Aldridge, Ross Bayton, Michael Dosmann, Tom Freeth, Dan Hinkley, Brian Humphrey, Eike Jablonski, Ned Lomax, Guillaume Mamdy, Helen Picton and Joanne Everson who have all helped piece together the curiously complex story of this plant in cultivation.