Lilium ukeyuri

Ukeyuri/ウケユリ (Uke'shima lily)

Veitch ex R.Hogg

Overview

• Synonym: Lilium alexandrae (Baker) Coutts
• Section: Archelirion
• Origin: Northern Nansei Islands, principally the Amami Islands of Kagoshima Prefecture, Japan
• Habitat: Exposed rocky slopes, cliffs, forest margins, and humid maritime island habitats
• Conservation status: Critically Endangered in Japan

Introduction

Lilium ukeyuri is one of Japan's rarest native lilies and one of the most geographically restricted members of the genus Lilium. It is an island endemic of the northern Nansei or Ryukyu archipelago, centered in the Amami Islands of Kagoshima Prefecture.

The species bears large, fragrant white trumpet-shaped flowers and belongs to the East Asian section Archelirion, which includes the Oriental lilies. Its highly restricted island distribution and distinctive maritime ecology make it particularly important for understanding the evolution and conservation of the Japanese island lilies.

The plant has a complicated nomenclatural history. For much of the twentieth century it was widely known in botanical and horticultural literature as Lilium alexandrae. Current taxonomic treatments, however, recognize Lilium ukeyuri (Veitch ex. R.Hogg) as the accepted name and treat Lilium alexandrae (Baker) Coutts as a synonym of the same species.

Accordingly, Lilium alexandrae should not be regarded as a separate species from L. ukeyuri.

Taxonomy and Nomenclature

The accepted name Lilium ukeyuri )(Veitch ex R.Hogg) was published in 1893.

The name alexandrae originated the same year when Baker described Lilium japonicum var. alexandrae. The plant was subsequently transferred among several different species and ranks as botanists attempted to understand the relationships among the white-flowered Japanese trumpet lilies.

Historical combinations include:

• Lilium japonicum var. alexandrae (Baker)
• Lilium brownii var. alexandrae (Baker) G.Nicholson
• Lilium longiflorum var. alexandrae (Baker) E.H.Wilson
• Lilium makinoi var. alexandrae (Baker) Makino & Nemoto
• Lilium alexandrae (Baker) Coutts

Current taxonomic authorities treat these names as synonyms of Lilium ukeyuri.

Importantly, Lilium alexandrae is a homotypic synonym of Lilium ukeyuri. The two names therefore do not represent two separately described island populations that were later combined; they are nomenclatural names referring to the same taxonomic entity.

The persistence of alexandrae in horticultural literature explains why the name remains familiar to lily growers and hybridizers today.

Distribution

Lilium ukeyuri is endemic to the northern Nansei Islands of southern Japan and is particularly associated with the Amami archipelago.

Documented populations have occurred on islands including Amami Ōshima, Kakeromajima, Ukejima, Yorojima, and Tokunoshima. Its distribution is highly fragmented, with individual populations separated by sea channels, steep terrain, and unsuitable habitat.

Ukejima is particularly associated with the species and gives the lily its Japanese and scientific vernacular identity. Populations there have received protection as a natural monument.

The species should not be described as a separate Yakushima endemic under the name Lilium alexandrae. Historical literature surrounding the name alexandrae contributed considerable confusion regarding the distribution of this taxon.

In the wild, Lilium ukeyuri is an inhabitant of humid subtropical slopes in the central Ryukyus. Ukejima is an island southeast of Kakeromajima, from which it is separated by a narrow strait. The second smallest inhabited island in the archipelago, the island has an area of 13.34 square kilometres (5.15 sq mi). The highest point, Mount Ōyama is 400 metres (1,300 ft) above sea level. The coast of the island is surrounded by a coral reef. As with nearby Yoroshima to the northwest, the island is noted for its high density of habu poisonous vipers.

The climate of Ukejima is classified as has a humid subtropical climate (Köppen climate classification Cfa) with very warm summers and mild winters. The rainy season lasts from May through September. It is distinctly maritime, with warm, humid summers influenced by the East Asian monsoon and mild, nearly frost-free winters. Cloud immersion, ocean winds, and frequent precipitation dominate its ecological environment.

The island is subject to frequent typhoons.

Description

Lilium ukeyuri is a perennial bulbous geophyte producing an erect to somewhat arching stem bearing narrow to lanceolate green leaves.

The flowers are large, white, trumpet-shaped, and strongly fragrant. They are generally carried horizontally or somewhat outward from the stem. The tepals broaden gradually from the floral tube and may show greenish or yellow-green coloration toward the throat or on the exterior.

The overall flower form resembles other white-flowered island lilies of southern Japan, especially L. longiflorum and L. nobilissimum. This similarity contributed greatly to the historical taxonomic confusion surrounding the species.

Plants are variable in stature depending on exposure, substrate, moisture availability, and competition from surrounding vegetation.

Habitat and Ecology

Lilium ukeyuri occupies a strongly maritime island environment influenced by high humidity, frequent rainfall, ocean winds, monsoonal weather, and periodic typhoons.

Wild populations occur on rocky slopes, cliff faces, open forest margins, scrub margins, and other relatively open habitats where competing vegetation does not completely shade the plants.

Field observations indicate that populations can occupy steep and sometimes nearly inaccessible rocky slopes. Such sites may provide several ecological advantages: reduced competition, rapid drainage, high aeration around the root zone, exposure to maritime airflow, and periodic disturbance caused by storms and slope instability.

The species therefore should not be characterized simply as a deep-forest lily. Although it occurs within humid subtropical vegetation zones, many populations occupy comparatively open or disturbed sites within the broader forested landscape.

Flowering occurs during the warm season, when the Amami Islands experience high humidity and substantial rainfall.

The Name Lilium alexandrae

The name Lilium alexandrae has a long history in lily literature and remains significant horticulturally.

Older books and breeding records frequently refer to alexandrae as though it were an independent species. As a result, many twentieth-century hybrid pedigrees retain the name L. alexandrae, and those historical names should generally be preserved when documenting the original breeding record.

Thus a historical hybrid recorded as:

Lilium alexandrae × Lilium speciosum

should not necessarily have its pedigree retrospectively rewritten, because alexandrae is the name under which the parent was identified by the breeder.

In modern taxonomic discussion, however, that parent belongs to the species now accepted as Lilium ukeyuri (syn. Lilium alexandrae)

This distinction allows historical horticultural records to remain intelligible without perpetuating the idea that alexandrae and ukeyuri are separate wild species.

Relationship to Other Ryukyu Lilies

The white-flowered trumpet lilies of the Ryukyu and Nansei island chain have been repeatedly confused because of their superficial similarity.

Modern treatments recognize three particularly important white-trumpet lilies within this island system:

• Lilium ukeyuri: Amami and neighboring northern Nansei islands

• Lilium nobilissimum: an extremely localized and critically endangered island endemic of the Tokara group found only a Kuchi no shima island.

• Lilium longiflorum: considerably more widespread through the Ryukyu island chain and adjacent regions

Lilium alexandrae should not be added to this group as a fourth species because it is a synonym of L. ukeyuri.

The similarity among these lilies reflects both common ancestry and adaptation to maritime island environments, but their taxonomic histories have been complicated by repeated transfers between species and varieties.

Relationship with Lilium nobilissimum the Emperor Lily

Lilium nobilissimum is a distinct species and another extremely localized white-flowered island lily of southern Japan.

Both L. nobilissimum and L. ukeyuri possess large fragrant white trumpet flowers and very restricted island ranges. Their resemblance led to considerable confusion in historical horticultural and botanical literature.

Modern taxonomic work, particularly the detailed treatment by James Compton in 2021, clarified their nomenclature and supported recognition of both as distinct critically endangered Ryukyu island species.

Thus:

• Lilium ukeyuri = Lilium alexandrae

but...

• Lilium ukeyuri ≠ Lilium nobilissimum

Horticultural History and Hybridization

Under the historical name Lilium alexandrae, this species became an important parent in twentieth-century Oriental lily breeding.

Its refined white trumpet form, fragrance, and relationship to other Archelirion lilies attracted breeders seeking to combine its floral qualities with species such as Lilium speciosum, L. rubellum, and L. nobilissimum.

Consequently, the name alexandrae appears frequently in historical hybrid pedigrees.

Breeding records using alexandrae remain valuable because they document the identity under which the plant circulated horticulturally at the time. Modern taxonomic references should simply note that this name is now treated as synonymous with L. ukeyuri.

This is an important example of the difference between historical horticultural nomenclature and current botanical taxonomy.

Cultivation

Lilium ukeyuri is uncommon in cultivation and should be maintained only from legally propagated material of documented origin.

Its native ecology suggests a preference for a rocky highly aerated, freely draining root environment combined with reliable moisture during active growth. Strong air circulation and protection from stagnant summer conditions are likely important.

Because populations occur in a humid maritime climate, cultivation should not attempt to reproduce humidity by creating stagnant, waterlogged soil. Instead, moisture should be combined with excellent drainage and root-zone aeration.

Partial sun or bright filtered light is appropriate, although conditions should reflect the provenance of individual cultivated material.

Because the species is critically endangered, careful provenance records should accompany cultivated stocks whenever possible.

Conservation

Lilium ukeyuri is considered Critically Endangered in Japan.

Its vulnerability results primarily from its extremely restricted and fragmented distribution. Small island populations are inherently susceptible to habitat disturbance, development, vegetation change, landslides, typhoons, collecting, invasive animals, and other stochastic events.

The loss of even a single population may represent the disappearance of a substantial portion of the remaining genetic diversity of the species.

Conservation therefore requires protection of existing wild populations together with carefully documented ex-situ cultivation, seed preservation, and propagation from legally obtained material.

For conservation collections, plants should ideally be maintained with locality or provenance information rather than being treated as interchangeable representatives of the species. The isolation of populations among different islands may preserve locally important genetic variation.

Evolutionary Significance

Lilium ukeyuri illustrates the importance of islands in the diversification of Lilium.

The Nansei archipelago forms a long chain between Kyushu and Taiwan. Repeated changes in sea level, climatic conditions, geological isolation, migration, and local extinction have produced a complex biogeographic history throughout the region.

The highly restricted distributions of L. ukeyuri and L. nobilissimum, compared with the broader distribution of L. longiflorum, provide an especially useful system for investigating how dispersal and isolation influence lily evolution.

The taxonomic history of L. ukeyuri also demonstrates why historical names must be interpreted cautiously. The long-used name Lilium alexandrae represents an important chapter in horticultural history, but it does not represent an additional living species in the modern flora.

Synonymy

Accepted name

Lilium ukeyuri (Veitch ex R.Hogg)

Homotypic synonyms

• Lilium alexandrae (Baker) Coutts
• Lilium brownii var. alexandrae (Baker) G.Nicholson
• Lilium japonicum var. alexandrae Baker
• Lilium longiflorum var. alexandrae (Baker) E.H.Wilson
• Lilium makinoi var. alexandrae (Baker) Makino & Nemoto

Selected References

Compton, J.A. 2021. “Two Endemic and Critically Endangered Ryukyu Island Lilies Lilium nobilissimum and Lilium ukeyuri (Liliaceae).” Curtis's Botanical Magazine 38: 240–259.

Royal Botanic Gardens, Kew. Plants of the World Online. Lilium ukeyuri Veitch ex R.Hogg.

Royal Botanic Gardens, Kew. Plants of the World Online. Lilium alexandrae (Baker) Coutts. Treated as a synonym of Lilium ukeyuri.

Flora of Japan IVb. Treatment of Lilium ukeyuri and associated nomenclature.