Parallel Paths of Beauty: Pollination Syndromes and Convergent Evolution in Lilies and Other Angiosperms
By Bret Hansen- Lilium Species Foundation 2025
Introduction
Flowers are among nature’s most intricate examples of design shaped by ecological relationships. Their diversity in form, color, and scent reflects millions of years of adaptation to the preferences and anatomy of their pollinators. The concept that specific suites of floral traits evolve in response to particular pollinators is known as a pollination syndrome.
A pollination syndrome encompasses the combined features of a flower, its color, fragrance, shape, timing of bloom, and nectar production, that have evolved through selective pressure by one or more pollinators. These features are not random; they represent a recurring pattern of convergence across unrelated plant lineages that rely on the same animal visitors.
The genus Lilium offers one of the most striking examples of this phenomenon. Across its range in the Northern Hemisphere, lilies have evolved into nearly every major pollination type, bee, butterfly, moth, and bird. Many share similar shapes and colors even when separated by continents or genetic lineage. This paper examines how pollination syndromes and convergent evolution have shaped Lilium species, particularly the North American lilies, and explores similar patterns among other flowering plants.
Pollination Syndromes and Floral Adaptation
Flowers do not evolve in isolation. Their forms and functions are molded by the behavior, vision, and feeding structures of their pollinators. Over time, the most efficient pollinators act as selective agents, favoring traits that improve pollen transfer.
Classical pollination ecology identifies several recurring syndromes:
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Bee pollination (melittophily) — blue, purple, or yellow flowers with sweet scent and UV nectar guides.
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Butterfly pollination (psychophily) — bright orange or red flowers with broad landing surfaces.
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Moth pollination (phalaenophily) — pale, night-opening flowers with strong evening fragrance.
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Bird pollination (ornithophily) — red or orange, unscented, nectar-rich flowers with tubular or recurved corollas.
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Fly or beetle pollination (myophily and cantharophily) — dull, often foul-scented flowers adapted to carrion or fruit visitors.
These syndromes do not reflect strict categories, but rather evolutionary trends: predictable combinations of traits that have arisen again and again in response to the same ecological pressures.
Within Lilium, nearly all of these syndromes can be found, making the genus an ideal model for studying pollinator-driven convergence.
North American Lilies: Color and Pattern Convergence
The lilies of western and eastern North America provide some of the clearest evidence for convergent floral evolution.
Species of the Western Coast of the United States such as Lilium columbianum, L. pardalinum, L. occidentale, L. parvum, share a remarkable similarity in flower morphology as their Midwestern and Eastern coast realitives L. canadense, L. pyrophillum, L. superbum, and L. michiganense share remarkably similar flowers: downward-facing, bright red to orange tepals with yellow throats and dark spotting.
Yet genetic studies show that these species belong to different subsections within the section psedolirium and are only distantly related. The similarities arise not from shared ancestry, but from shared pollinators, particularly hummingbirds and butterflies.
Their recurved “Turk’s cap” flowers position the stigma and anthers precisely where a hovering bird’s head or tongue will brush them, ensuring effective pollen transfer.
Even species adapted to different environments, from coastal wetlands (L. occidentale) to inland mountain meadows (L. parvum), have converged on nearly identical floral patterns. The same visual and structural cues, brilliant red coloration, absence of scent, and reflexed tepals, signal hummingbirds while deterring bees, which cannot perceive red.
This convergence among unrelated North American lilies exemplifies how pollinator-driven selection shapes floral form independently of genetic lineage.
Fragrant Tubular Lilies and the Moth Pollination Syndrome
If the North American lilies illustrate convergence under bird pollination, their Asiatic and Western American counterparts reveal a parallel evolutionary path shaped by moths.
Species such as Lilium formosanum,L. longiflorum, L. nobilissimum, L. japonicum, L. alexandrae, and L. ukeyuri bear long, narrow trumpet-shaped flowers, typically white or pale pink, and release a rich fragrance strongest at dusk. These traits correspond to the moth pollination syndrome: pale coloration for nocturnal visibility, deep floral tubes matched to the long proboscises of sphinx moths (Sphingidae), and powerful evening scent that serves as a chemical beacon in still air.
Similarly, several Western American lilies, including L. washingtonianum, L. parryii, and L. rubescens, have independently evolved the same set of traits. Each produces tubular trumpets that narrow into a deep nectar tube and emit a powerfully intoxicating fragrance, especially at night to attract hawkmoths. Though these American and Asian species belong to different clades and sections within Lilium, their near-identical floral design reflects convergent adaptation to the same ecological niche.
Other unrelated genera demonstrate this same pattern, Nicotiana alata, Yucca filamentosa, and Oenothera biennis, for instance, all open white, sweet-scented, night-blooming flowers for hawkmoth pollination. Across continents and families, moth-pollinated plants have repeatedly evolved long, tubular, fragrant blossoms that function as precise invitations to the night.
These traits correspond to the moth pollination syndrome: nocturnal opening, pale coloration for night visibility, and powerful scent cues that attract sphinx moths (Sphingidae).
The moth’s long proboscis matches the floral tube’s depth, while hovering behavior allows access to deep nectar reservoirs.
Interestingly, these Asian species belong to separate evolutionary lineages within Lilium—Leucolirion and Archelirion, but their nearly identical floral morphology shows that the same ecological niche can sculpt unrelated taxa into parallel forms.
Other genera display the same adaptation: Nicotiana alata (flowering tobacco), Yucca filamentosa, and evening primroses (Oenothera spp.) all open fragrant white flowers at night to attract hawkmoths.
Together, these examples show how moth-pollinated flowers have independently evolved convergent tubular morphology, fragrance chemistry, and timing across the plant kingdom.
Beyond Lilies: The Lily Form Across the Angiosperms
The “lily shape” is so recurrent that it appears across multiple plant families that are not even closely related.
Amaryllids such as Hippeastrum reginae, alstroemerias (Alstroemeria aurea, Bomarea edulis), and daylilies (Hemerocallis fulva) all exhibit six tepals, a symmetrical perianth, and a central pistil surrounded by six stamens—yet each lineage evolved these traits independently.
In some, such as Hippeastrum, the resemblance to Lilium is so close that early taxonomists confused the two.
This morphological convergence arises because similar pollinators, often hummingbirds or large bees, select for the same efficient floral architecture.
Pollination syndromes thus explain why “lily-like” flowers occur throughout the angiosperms, from tropical rainforests to alpine meadows, and why visual similarity can mask deep genetic divergence.
Convergent Evolution and Phylogenetic Insight
Before molecular phylogenetics, botanists relied heavily on floral morphology to classify plants.
This led to taxonomic groupings based on shared flower form rather than shared ancestry.
Modern DNA studies of Lilium (Nishikawa et al. 1999; Kim et al. 2011; Duan et al. 2022) have clarified that the classic flower types, “trumpet,” “Turk’s cap,” “bowl”, are the products of parallel evolution rather than indicators of relationship.
For example, the reflexed red flowers of L. martagon in Eurasia and L. columbianum in North America evolved independently, each shaped by pollinators with similar feeding behaviors.
Molecular data now confirm that flower morphology is often a reflection of ecology, not genealogy.
Recognizing this distinction prevents misclassification and deepens understanding of how pollinators drive diversification across the genus.
Interdependence and Pollinator Cascade Effects
Hawkmoth-pollinated lilies rely not only on the presence of their pollinators, but also on the persistence of the larval host plants that sustain those pollinators.
Hawkmoth larvae feed on a wide range of host species, notably evening primroses (Oenothera), fireweeds (Epilobium), nightshades (Nicotiana, Datura), and wild vines (Vitis, Ipomoea).
In both East Asia and North America, these host plants coexist with trumpet-flowered lilies, forming complex ecological networks in which each species’ survival indirectly supports the others.
Loss of host plants leads to the decline of moth populations and consequently disrupts lily pollination.
Over time, this can trigger evolutionary shifts in floral traits, favoring new colors, scents, or morphologies adapted to alternative pollinators.
Such pollinator replacement and morphological drift may explain the variation between related species such as Lilium parryii and L. washingtonianum, or between Asian trumpet lilies and their less-specialized descendants.
Flower morphology is largely driven by pollinator preference.
When primary pollinators decline, plants become increasingly dependent on secondary or opportunistic visitors that may be less effective at transferring pollen.
If these new visitors become the dominant pollinators, they exert a different set of selective pressures, favoring floral traits that better match their sensory and behavioral profiles.
A single mutation that slightly alters flower color, fragrance, or shape may suddenly make a flower more attractive to these new pollinators, increasing its reproductive success and spreading that trait through the population.
Conversely, if secondary pollinators are less responsive to features favored by the former pollinator, such as long floral tubes, specific fragrances, or bright hues, those traits may gradually decline, giving rise to new floral morphologies better suited to the prevailing pollination environment.
The interdependence among moths, their larval hosts, and lilies exemplifies the delicate web of evolutionary feedbacks that sustain both floral diversity and ecological resilience.
In this sense, the loss of a single larval host species may cascade through an ecosystem, reshaping not only the fate of pollinators but the evolution of the flowers they visit.
Habitat Alteration, Disturbance Regimes, and Pollination Efficiency
Pollinators do not depend solely on flowers for their survival; they also rely on the environmental conditions that support their life cycles, including the presence of larval host plants, open flight corridors, and stable microclimates. When natural disturbance regimes such as wildfire, flooding, or seasonal drawdown are altered or suppressed by human activity, these critical conditions change. In ecosystems where lilies and their pollinators evolved, natural predicable periodic disturbance helps maintain open, sunlit habitats where flowers are visible and accessible. Fire and flooding, for instance, prevent dense shrub or tree cover from encroaching and help sustain the growth of host plants that moths, butterflies, and other pollinators depend on for their larvae. When these disturbances are suppressed, natural succession proceeds unchecked, vegetation thickens, and the flowers that once drew pollinators become hidden or difficult to access.
Pollinators are driven by efficiency. Their foraging behavior follows an energy economy: they seek to maximize nectar intake while minimizing effort. If flowers become too difficult to find or reach, whether obscured by overgrowth, located too sparsely across a landscape, or phenologically mismatched, pollinators move elsewhere to forage. In such cases, hummingbirds, moths, and other nectar-feeding species may simply abandon the area in favor of more accessible floral resources. This decline in visitation leads to reduced pollen transfer, lower seed set, and gradual reproductive decline for the plants that remain.
The problem deepens when larval host plants disappear from the landscape. Hawkmoths, for example, rely on evening primroses (Oenothera), fireweeds (Epilobium), nightshades (Nicotiana, Datura), and wild vines (Vitis, Ipomoea) to complete their life cycles. If these hosts vanish due to habitat alteration, the adult moth population cannot recover, and moth-pollinated lilies lose their principal pollinators. This represents a cascading ecological effect: changes in the distribution of host species ripple upward, reducing pollinator abundance and, in turn, lily reproduction.
As pollinator populations decline or shift, plants face new selective pressures. In the short term, they may rely on opportunistic visitors such as bees or butterflies that provide less efficient pollination. Over time, these new visitors can influence the direction of floral evolution.
Variations in color, fragrance, or flower shape that appeal to secondary pollinators may confer reproductive advantages, allowing those traits to spread through a population. Conversely, features that once favored the original pollinator, long floral tubes, nocturnal scent release, or bright but specific hues, may decline if they no longer attract visitors. In this way, habitat alteration and pollinator decline can indirectly drive the transformation of floral morphology and behavior, a process known as pollinator shift.
Ultimately, evolution is not about perfection but efficiency. Plants and pollinators coevolve to optimize energy use within the constraints of their environment. When humans alter those environments, through fire suppression, drainage, or habitat fragmentation, the delicate balance that sustains these relationships breaks down. Restoring natural disturbance regimes, preserving host plant diversity, and maintaining open, connected landscapes are therefore essential not only for conserving pollinators but also for preserving the evolutionary trajectories of the lilies and other flowers that depend on them.
Ecological and Evolutionary Implications
Pollination syndromes reveal the dynamic balance between specialization and resilience.
Highly specialized flowers achieve efficient pollination but risk collapse if their pollinators decline.
Hummingbird-dependent lilies, for instance, are vulnerable to habitat changes that reduce nectar-feeding bird populations. If hummingbirds are forced to relocate do to habitat destruction, loss of food resources, or simply that their prefered habitat is no longer suitable do to natural sucession becuse of wildfire supression or hydrological alteration, the plants and lilies that depend on them for pollination are faced with few good options to mitigate the loss of their primarly pollinator, usualy the best bad option. And usualy they can't adapt fast enough to stop population collapse.
Conversely, generalist pollination systems can buffer species against ecological instability but may reduce reproductive precision.
Environmental factors—altitude, light, humidity, and temperature—further refine how these interactions play out across landscapes.
The repetition of the same floral solutions in different places demonstrates how evolution repeatedly finds the same answer to similar ecological problems.
Conclusion
The genus Lilium illustrates the unity of evolutionary design across diversity.
Whether the bird-pollinated lilies of North America or the moth-pollinated trumpets of Asia, the same forces—pollinator behavior, physiology, and environment—sculpt their beauty.
This convergence of form underscores a profound truth: flowers are not shaped by ancestry alone but by relationship—by the intimate dialogue between plant and pollinator.
Through that dialogue, evolution has painted the world in recurring patterns of color, scent, and symmetry—reminding us that nature’s artistry, however diverse, often follows the same brushstrokes.
Works Cited
- Duan, T., et al. 2022. “Phylogeny and Divergence Time Estimation of Lilium (Liliaceae) Based on Plastid Genomes.” Frontiers in Plant Science 13: 1–12.
- Faegri, K., and L. van der Pijl. 1979. The Principles of Pollination Ecology. 3rd ed. Pergamon Press.
- Fenster, C. B., Armbruster, W. S., Wilson, P., Dudash, M. R., and Thomson, - J. D. 2004. “Pollination Syndromes and Floral Specialization.” Annual Review of Ecology, Evolution, and Systematics 35: 375–403.
- Grant, V., and Grant, K. A. 1968. Hummingbirds and Their Flowers. Columbia University Press.
- Kim, J. H., et al. 2011. “Molecular Phylogenetics of the Genus Lilium and Related Genera.” Plant Systematics and Evolution 295: 145–159.
- McRae, E. A. 1998. Lilies: A Guide for Growers and Collectors. Timber Press.
- Nishikawa, T., et al. 1999. “Molecular Phylogeny of the Genus Lilium Inferred from ITS Sequences.” Theoretical and Applied Genetics 98: 954–961.
- Proctor, M., Yeo, P., and Lack, A. 1996. The Natural History of Pollination. HarperCollins.
- Thomson, J. D., and Wilson, P. 2008. “Explaining Evolutionary Convergence in Floral Function.” Trends in Ecology & Evolution 23 (5): 310–316.
- Waser & Campbell (2004) “Ecological Speciation in Flowering Plants” — pollinator replacement can shift floral phenotype within a few hundred generations.
- Thomson & Wilson (2008) “Explaining Evolutionary Convergence in Floral Function” — same ecological process you describe.
- Bradshaw & Schemske (2003) Nature — a single gene mutation changing flower color in Mimulus caused a shift from bee to hummingbird pollination.
References for This Section
• Bond, W. J., and Keeley, J. E. 2005. 'Fire as a Global ‘Herbivore’: The Ecology and Evolution of Flammable Ecosystems.' Trends in Ecology & Evolution 20(7): 387–394.
• Keeley, J. E., Pausas, J. G., Rundel, P. W., Bond, W. J., and Bradstock, R. A. 2011. 'Fire as an Evolutionary Pressure Shaping Plant Traits.' Trends in Plant Science 16(8): 406–411.
• Pickett, S. T. A., and White, P. S., eds. 1985. The Ecology of Natural Disturbance and Patch Dynamics. Academic Press.
• Raguso, R. A. 2004. 'Why Are Some Floral Nectars Scented? Ecology, Evolution, and Biochemistry of the Floral Volatiles.' Ecology Letters 7: 495–503.
• Waser, N. M., and Campbell, D. R. 2004. 'Ecological Speciation in Flowering Plants.' Proceedings of the Royal Society B 271(1551): 2781–2790.