In this study, we describe Lilium huanglongense, a newly-discovered lily species identified following extensive surveys in an undeveloped area of the Huanglong National Nature Reserve in Sichuan, China. This region, located in the Hengduan Mountains of south-western China, is recognised as one of the world’s prominent biodiversity hotspots, providing diverse habitats for a wide range of plant species. Morphologically, L. huanglongense resembles Lilium fargesii Franch., which is distributed in central China, as well as other tepal-recurved members of the section Lophophora (Bureau & Franch.) F. T. Wang & Ts. Tang. This section comprises dwarf lilies predominantly found in the alpine scrub of the Hengduan Mountains, extending westwards into the Himalayas. Molecular phylogenetic analyses using both nuclear ITS and chloroplast genomes confirm the independent status of the new species and its placement within the section Lophophora. The identification of this new species helps to fill the distribution gap between broad-leaved forest and alpine scrub species within the section, thereby enhancing our understanding of the diversity and distribution history of Lophophora.

Liliaceae, Lilium huanglongense, Lophophorum-clade, new species, section Lophophora

Lilium, a genus in the tribe Lilieae of the family Liliaceae, comprises herbaceous, bulbous plants with scaled bulbs, dorsifixed anthers and loculicidal capsules (Peruzzi 2016). With approximately 123 recognised species (POWO 2024), the genus is widely distributed across the Northern Hemisphere in Asia, Europe and North America (Liang and Tamura 2000). China, in particular, hosts approximately 55 distinct species according to the latest flora records (Liang 1995; Liang and Tamura 2000), with key distribution areas including northeast, central and south-western China. Amongst these regions, south-western China stands out as a hotspot for the diversity of wild lilies due to its mountainous environment (Gao et al. 2013b, 2015). These mountain ranges and deep valleys constitute an intricate topography, which provides unique habitats for various species.

The Daba Mountains and the Qinling Mountains of central China, as well as the Hengduan Mountains and the Himalayas, form a series of mountain ranges from central to western China, together harbouring the greatest number of lilies in the world (Yundong Gao, unpublished data). Furthermore, the rugged terrain and sparse population in mountainous regions have constrained previous explorations, indicating the potential presence of undiscovered species in these areas. Investigating plant groups within these continuous mountain ranges would enhance our understanding of species diversification and dispersal history amongst the selected plant species, thereby contributing significantly to our overall knowledge of biodiversity.

Our prior investigation elucidated the taxonomic classification of the genus Lilium (Gao et al. 2012, 2013b, 2015; Gao and Gao 2016; Yuan and Gao 2024). Specifically, the Lophophorum-clade sensu Gao et al. (2013b) was identified, which comprises both the campanulate-flowered L. oxypetalum Baker, L. lophophorum (Bureau & Franch.) Franch., L. nanum Klotzsch, as well as the tepal-recurved L. fargesii Franch., L. stewartianum Balf. f. & W.W. Sm. and L. matangense J.M. Xu that span mountainous regions from central China (broad-leaved forests) to the Himalayas (alpine scrub and meadows). This clade is analogous to the subgeneric section Lophophora (Bureau & Franch.) F. T. Wang & Ts. Tang, as refined by Watanabe et al. (2021) in their recent work. Most members of this clade, which exhibit recurved perianths, have a limited and sporadic distribution. For example, L. fargesii exhibits a notable widespread distribution at mid-elevation areas (second step) in China (mainly in Qinling and Daba Mountains), while L. matangense is found further westwards at higher altitudes of over 3000 m, with narrow distribution and very small population sizes and therefore is of conservation value. Additionally, L. stewartianum is distributed at an altitude of about 3500 m in the southern Hengduan Mountains (Fig. 1).

Figure 1. 

Morphological characteristics and geographic distribution of Lilium huanglongense and related species. Lilium huanglongense fills the geographic gap west of the Qinling Mountains and at the confluence of the Hengduan Mountains.

With advancements in molecular phylogenetics, the monophyly of the Lophophorum-clade has been confirmed (Gao et al. 2013b; Watanabe et al. 2021); however, our understanding of its composition and evolutionary history remains incomplete. Moreover, the distribution of the entire Lophophorum-clade is disjunctive (Fig. 1), particularly between the northern Hengduan Mountains and the western Qinling Mountains, creating a “gap” where members of this clade have not been previously documented. This relic distribution pattern may suggest the presence of additional undiscovered taxa or those that are already extinct. In recent years, meticulous sampling and analysis of this group have yielded several novel findings. This paper highlights one such discovery: the putative new species L. huanglongense, identified by rangers in the Huanglong National Nature Reserve. This discovery can be partially attributed to the increased attention that the Chinese government has directed towards nature reserves and it represents a significant advancement in our understanding of this clade.

Currently, we aim to clarify the status and phylogenetic position of the putative new species by comparing its morphology with that of the most morphologically similar species, in addition to conducting molecular phylogenetic analyses utilising both nuclear markers and chloroplast genomes. Furthermore, the analysis of the morphological and genetic distinctiveness of L. huanglongense is expected to offer additional insights into the Lophophorum-clade by addressing the geographic distribution gap observed amongst its members.

Previously, we documented the presence of two distinct flower morphologies within the Lophophorum-clade, which may reflect parallel evolution as lilies rapidly adapt to diverse environments (Gao et al. 2015; Yuan and Gao 2024). This suggests that the former classification of Lilium into subgenera, based solely on floral morphological differences, may not be entirely valid (Watanabe et al. 2021). The Lophophorum-clade further supports the notion that parallel evolution is prevalent within the genus Lilium (Gao et al. 2015; Yuan and Gao 2024). Consequently, caution is warranted when assessing subgeneric affinities, based exclusively on morphological characteristics in this genus.

Molecular phylogenetic analysis demonstrated that Lilium huanglongense occupies a distinct position within the Lophophorum-clade. The Maximum Likelihood (ML) tree, based on chloroplast data, shows L. huanglongense as sister to L. nanum, L. lophophorum, L. matangense and L. stewartianum (Fig. 5A). In contrast, both the ML and Bayesian Inference (BI) trees, based on ITS data, place L. huanglongense and L. stewartianum in a monophyletic group (Fig. 5B), revealing a discordance between nuclear and plastid phylogenies (Fig. 5). This discrepancy may result from incomplete lineage sorting (ILS) and introgression. However, our previous studies suggest that plastid phylogeny better reflects the geographic relationships amongst species, with introgression being a more plausible explanation (Gao et al. 2013b, 2015).

Within the plastid genome tree, Lilium fargesii occupies the earliest diverging position within the Lophophorum clade-clade (Fig. 5A). The emergence of L. huanglongense may have occurred during times of environmental fluctuation, such as the Quaternary Ice Age, followed by subsequent environmental isolation from its potential ancestral species during interglacial periods (Davis et al. 2005). This aligns with the observed distribution pattern, indicating that L. huanglongense is confined to a unique geographic position within the entire clade (Fig. 1), similar to other tepal-recurved members (e.g. L. matangense, L. stewartianum, Fig. 1) that are sporadically distributed in the Hengduan Mountains region. The limited population size and few populations of these tepal-recurved members of the Lophophorum clade clade suggest that a widely-distributed common ancestor may have existed previously, with the current relic pattern resulting from long-term isolation.

Morphologically, Lilium huanglongense is characterised by its compact stature, pale yellow perianth (Fig. 2A), flattened and delicate floral structure and dense basal foliage, distinguishing it from morphologically similar species. The pale yellow perianth of L. huanglongense sets it apart from L. matangense (Fig. 2C) and L. fargesii (Fig. 2D), which typically exhibit flowers with perianth colours ranging from white to green. Additionally, its relatively small size and flattened floral structure (short tube length) differentiate it from L. stewartianum (Fig. 2E), which features a deep, slender floral funnel (the height of the cone formed by the connivent tepals). Our comparisons also revealed significant differences in the proportions of floral organs amongst these species. Lilium huanglongense has flattened floral parts, with the flowers and stamens nearly in the same plane (Fig. 2A). In contrast, the pistils and stamens of similar species, such as L. fargesii, L. stewartianum and L. matangense, clearly protrude from the perianth.

The specialised perigone structure in L. huanglongense is likely the result of localised plant-environment interactions, particularly with its pollinators. These pollinators play a crucial role in driving morphological evolution (Van der Niet and Johnson 2012; Van der Niet et al. 2014) and have influenced the delicate floral features of L. huanglongense, such as its pale yellow perianth and flattened floral structure, which may have evolved to attract specific pollinators in its habitat. Lilium huanglongense exhibits a shorter style than L. fargesii and a shorter floral tube (the height of the cone formed by the connivent tepals) than L. stewartianum. These differences in floral morphology may have evolved in response to varying pollinators, indicating that pollination syndrome may play a key role in the speciation process of this new species.

Geographically, Lilium huanglongense bridges the distribution gap between L. fargesii, native to central China and other species inhabiting the south-western alpine mountains (Fig. 1). The entire Lophophorum-clade extends over a broad geographic range from Hunan (L. fargesii) in the east to the western Himalayas (L. nanum) in the west. This distribution encompasses mesic broadleaf forests in the central Daba Mountain system, alpine scrublands in the south-western Hengduan Mountains and extends to the alpine scrub meadows of the Himalayas (Gao et al. 2013b). The divergence of the Lophophorum clade clade is likely due to historical geological and climatic changes in the Qinling-Dabashan-Hengduan-Himalayan region (Gao et al. 2013b; Xing and Ree 2017). This region, characterised by a series of mountain ranges and diverse ecological niches, spans central and south-western China and supports substantial biodiversity.

In conclusion, Lilium huanglongense is a morphologically and molecularly distinct new species within the Lophophorum-clade. This discovery not only contributes to the diversity of the genus, but also fills a geographical gap west of the Qinling Mountains, at the confluence of the Hengduan Mountains. However, our understanding of the Lophophorum-clade remains incomplete. To enhance our comprehension of its phylogenetic relationships and gain a comprehensive understanding of the biogeographic processes involved, further literature reviews, fieldwork and additional collection of morphological and molecular data are necessary.

We gratefully acknowledge Professor Xin-Fen Gao and Ms. Qi Yu of Chengdu Institute of Biology, Professor Changqiu Liu of Guangxi Institute of Botany, Dr. Pan Li of Zhejiang University and Mr. Melvyn Herbert for their support with sample collection. We appreciate Xiao-Juan Chen’s assistance with the software and article submission.