Nectar, the original cocktail: an introduction to a Virtual Issue

Abstract

The interaction between flowering plants (angiosperms) and their animal pollinators is one of the most studied mutualisms between animals and plants. In both ancient Greece and Chinese culture, nectar is referenced as divine and heavenly blessed. In Homer's Iliad, nectar is described as the drink of the gods and, similarly, in ancient Chinese folklore, 甘露 (gān lù, literally ‘sweet dew’) is believed to be a heavenly elixir with the power to grant immortality. While these references likely do not refer to floral nectar as we understand it today, they underscore the cultural significance historically attributed to nectar-like substances.

Entering the modern scientific era, Charles Darwin, fascinated by what he called the ‘abominable mystery’ of the prolific evolution of flowering plants, suggested that nectar and nectaries evolved as adaptations to attract pollinators for outcrossing. He famously predicted the existence of a long-tongued moth capable of reaching nectar in the extended floral spur of Angraecum sesquipedale (Darwin, 1877), which was later confirmed by the discovery of Xanthopan morganii praedicta (Nilsson, 1988; Wasserthal, 1997). Building on Darwin's insights, subsequent botanical characterization has extensively documented and examined the structures of nectaries while ecological studies have examined the functions of nectar in nearly all major taxa of angiosperms with great detail (Bernardello, 2007; Nicolson et al., 2007; Erbar, 2014).

Despite the widespread occurrence of nectar secretion and the remarkable structural diversity of nectaries among flowering plants, little is known about the ecological significance of each of the nectar components, and molecular and genetic studies of nectary biology have been limited to a few model species, including Arabidopsis, Nicotiana, Petunia, Cucurbita, and Gossypium (Bowman & Smyth, 1999; Ren et al., 2007; Kram & Carter, 2009; Liu et al., 2009; Morel et al., 2018; Solhaug et al., 2019; Hu et al., 2020; Chatt et al., 2021). Studies using these genetic models have uncovered key regulators of nectary development, major processing genes of nectar sugar, and detailed chemical compositions of nectar (Bowman & Smyth, 1999; Kram et al., 2009; Ruhlmann et al., 2010; Lin et al., 2014; Morel et al., 2018; Hu et al., 2020; Pei et al., 2021). Yet, many fundamental questions remain unanswered. Is nectary development in independently evolved nectaries regulated by the same genetic networks? How is diversity in nectar composition generated and governed across taxa? What is the ecological significance of specialized metabolites in nectar? And at the most fundamental level, how many angiosperm species produce and secrete nectar?

In pursuit of these questions, New Phytologist has become a leading venue for reporting new findings in nectar biology research. This has inspired us to organize this Virtual Issue to highlight novel discoveries in understanding nectar and nectaries in recent years, particularly in the -omics era. The growing availability of high-quality genomes and updated phylogenies, along with the decreasing cost of transcriptomic, proteomic, and metabolomic analyses, has greatly expanded the range of nectary research.

Understanding the diversity and evolution of floral nectaries must start with an in-depth assessment of which species produce nectar. With the availability of modern molecular and sequence-based phylogenies, such large-scale analyses have become possible. The opening research article of this special collection provides an extensive examination of the distribution and prevalence of floral nectaries across angiosperms (Ballarin et al., 2024). Ballarin et al. compiled a database including 7621 plant species from 322 families to estimate the number and proportion of nectar-producing flowering plants among angiosperms. Based on their estimation, 223 308 species (or 74.4%) of animal-pollinated angiosperms produce nectar. Intriguingly, geographic distribution data from the surveyed species reveal a trend of increasing proportions of nectar-producing species at higher latitudes and elevations. This trend suggests that nectar is a more consistent reward in these geographic conditions, whereas species in warm, moist climates, such as the tropics diversify their floral rewards.

To understand nectary diversity at the molecular and cellular level, a clear framework of nectary development and function is essential. In this Virtual Issue, a review by Liao et al. (2025) provides such a framework, synthesizing major discoveries in nectary development and trends in nectary evolution across both model and nonmodel species. The authors categorize the types of floral nectaries based on the organization of the structure and the primary modes of secretion of these nectaries, using a developmental framework to address open questions in nectary biology and establish key points of comparison across diverse nectaries.

Studies using emerging nonmodel systems have yielded intriguing and exciting insights on nectary development and biology. The Ranunculaceae genus Aquilegia is one of the newly established models for nectary research. In Aquilegia, STYLISH – an unexpected family of transcription factors – was shown to be co-opted to control the nectary fate (Min et al., 2019). Interestingly, although Arabidopsis and Aquilegia evolved nectaries independently and use different upstream regulators to initiate nectary development, both lineages require the activities of Auxin Response Factors 6 and 8 for proper nectary formation. This suggests a complex evolutionary rewiring of the genetic network underlying nectary development (Zhang et al., 2020). Another exploration of the nectary development program, in this case in Mimulus, has uncovered a role for the pleiotropic locus STERILE APETALA in controlling the expression of the core eudicot nectary regulatory factor CRABS CLAW (Zhai et al., 2025, in this issue pp. 1116–1122). In a notable study of monocot nectaries, Mou et al. (2025) have described the first case of occurrence of postfloral nectar production from pollinated carpels in Dendrobium chrysotoxum (Orchidaceae) using anatomical, transcriptomic, and metabolomic studies. Field studies also revealed frequent ants visit to the carpels after successful pollination, raising the possibility that this post-floral nectar serves a defensive role, analogous to the antiherbivore function of extrafloral nectaries on leaves and stems. The spatial–temporal regulation of nectar secretion has long been a central theme in nectar biology. A recent contribution to this topic by Soares et al. (2025) demonstrated that in Passiflora extrafloral nectaries, the miR156-mediated plant aging clock is connected to the maturation of extrafloral nectaries and activation of nectar secretion. This study greatly extends the known temporal window in which nectary development programming is thought to operate and provides a plausible explanation of leaf-to-leaf variation in extrafloral nectary density and complexity in various plant lineages, including Passiflora and Turnera.

Of course, nectar is more than just a mixture of sugar and water. It often contains a variety of additional compounds, including amino acids, pigments, volatile organic compounds, and inorganic molecules, such as cations and hydrogen peroxide. The inclusion of these specialized compounds is believed to make nectar more visible, attractive, and stable. Studies are beginning to identify the genetic basis of specialized compounds, such as that of Grierson et al. (2024), who identified a phosphatase gene in Leptospermum scoparium (Mānuka) whose expression was linked to nectar dihydroxyacetone accumulation, the precursor of methylglyoxal, the antimicrobial compound that makes Mānuka honey so highly valued. However, can pollinators detect the presence of these compounds in the nectar and exert selection pressure on nectar chemistry? Parkinson et al. (2025) investigated this question by analyzing the composition of carbohydrates and essential amino acids in 102 nectar-producing plants in UK and tested bumblebee (Bombus terrestris) preference on this collection of nectar. Their studies demonstrate that essential amino acid profiles matter more for pollinator preference than the overall essential amino acid concentrations. Interestingly, they did not show a strong bumblebee preference for a specific amino acid profile (six were tested), except that they consistently avoided nectar with high concentrations of proline, suggesting a potential coevolution between angiosperms and pollinators driven by the nectar amino acid profile. In a complementary study, MacNeill et al. (2025) focused on the Salvia genus and examined the correlations between pollination syndrome shift and changes in nectar metabolome, where convergence of the ‘chemical pollination syndromes’ was reported. Species displayed similar nectar metabolomes across the same pollination syndrome, suggesting that nectar chemistry could be driven by pollinator gustatory preference. Together, these two studies paint a more complex picture of nectar-mediated plant–pollinator interactions, highlighting the importance of expanding our focus beyond sugars to include a wider range of nectar chemicals.

Pigment is a rare but effective nectar ingredient that can be a powerful driver of pollinator attraction. Recent work led by the research groups of Clay Carter and Adrian Hegeman has brought attention to this striking and understudied class of nectar components (Roy et al., 2022; Magner et al., 2023). Colored nectar has evolved independently at least 15 times in flowering plants and has been documented in 67 taxa (Hansen et al., 2007). Using an integrative multi-omics approach, including transcriptomics, proteomics, and metabolomics, Magner et al. (2023, 2024) uncovered the molecular basis of black nectar in Melianthus and yellow nectar in Capsicum. This comprehensive analysis enabled the identification of the precise chemical combinations responsible for nectar coloration. What is remarkable is that in both species, the conspicuous color is producedynthesized or secreted at anthesis, suggesting a regulatory mechanism through which plants can control the timing of nectar visibility. In the case of Capsicum, riboflavin, the coloring reagent, possesses antibacterial properties and may itself serve as a reward to the presumed pollinator. In addition to these exciting studies, Magner et al. (2025) also contributed a Tansley insight article summarizing the current understanding of the roles of colored nectar and reactive oxygen species in influencing pollinator behavior.

Far from being lifeless, nectar is a micro-ecosystem and harbors a dynamic and diverse community of microbes. This Virtual Issue includes an additional review by Quevedo-Caraballo et al. (2025), detailing the research on nectar microbes from the past decades. They revisit the origins and composition of nectar microbes, the effect of nectar microorganisms on nectar chemistry, and the current understanding of the intense competition between nectar yeasts and bacteria and their effect on visiting pollinators. Beyond summarizing current knowledge, the review also explores potential practical applications of nectar-associated bacteria in agriculture, such as enhancing pollinator visitation rates and mitigating the challenges of pathogens and herbivores.

Do plants actively sense and regulate the nectar microbiome? Hydrogen peroxide in nectar has long been proposed as a plant-derived defense mechanism to limit microbe growth (Carter & Thornburg, 2004; Carter et al., 2007; Alvarez-Perez et al., 2012). However, how widespread is hydrogen peroxide in floral nectar, and are the concentrations high enough to limit bacterial growth? Landucci & Vannette (2025) addressed this question by surveying 45 angiosperm species from 23 families to assess field-realistic levels of nectar hydrogen peroxide. While hydrogen peroxide was detectable in the majority of species, nearly half had concentrations below 100 μM, levels that are unlikely to provide effective antimicrobial defense. Nevertheless, the presence of hydrogen peroxide significantly influenced the composition of the nectar microbiome. Interestingly, co-growth of peroxide-sensitive and peroxide-tolerant microbes can facilitate the survival of both type of microbes, suggesting that microbial interactions may buffer the inhibitory effects of peroxide and allow for the coexistence of diverse microbial communities. These findings highlight the nuanced and context-dependent role of hydrogen peroxide in shaping nectar microbial colonization and persistence.

As a major food source for many animals, nectar rewards are important for many ecosystem functions with implications for species conservation and agricultural productivity. Studying genetic variation of nectar traits and floral honesty (signal-reward correlation) and its effect on plant fitness is not very well understood. From an evolutionary perspective, Romero-Bravo & Castellanos (2024) used Digitalis purpurea to explore phenotypic plasticity, heritability, evolvability, and integration of floral morphology and nectar, revealing that nectar traits are highly plastic and show a high potential to respond to selection. Experiments with Turnera velutina (Passifloraceae) incorporate the pollinator responses to floral and nectar signals, demonstrating that pollinators are able to distinguish individuals with honest signals and high nectar content from those with less honest signals or less nectar, the former resulting in higher seed set (Ramos et al., 2025). While honest floral signaling may be critical for the fitness of both plant and animal partners, designing habitats for conserving species requires knowing which plant species produce the most nectar, when they produce nectar, and the abundance of the plant species. In the case of the endangered Karner blue butterfly (Plebejus melissa samuelis), Turner et al. (2025) measured the nectar properties from 22 plant species across 15 oak savannas and determined two species, Rubus flagellaris and Ceanothus americanus, that contributed the highest nectar quality, thus informing decisions for future habitat restoration. Finally, beneficial nectar-related interactions are not always straightforward. As demonstrated by Grof-Tisza et al., one of the benefits of growing beans and maize together is the interplay between the parasites and herbivores: extrafloral nectar from beans sustains the survival of wasps, which parasitize caterpillars that feed on and damage maize leaves. In turn, herbivory-induced volatiles from maize lead to increased extrafloral nectar secretion (Grof-Tisza et al., 2025). These complex interactions reveal nectar-mediated mechanisms for increased productivity in mixed cropping agricultural systems through pest and damage control. Together, these studies reveal the multi-scale interactions of which nectar plays a role and the considerations necessary for applications in conservation and agriculture.

Although modest in volume, this Virtual Issue captures the current momentum and diversity of research in nectar and nectary biology – spanning ecology, evolution, development, and physiology. Together, these articles reflect a vibrant and expanding field, propelled by new technologies and fresh perspectives. As scientific discoveries continue to unfold, we are ever hopeful to be closer to a comprehensive understanding of how nectar has shaped the intricate relationships between angiosperms and their pollinators, and how the nectary structures first emerged and have evolved and diversified in the past 100 million years.

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