The leaves of the spring ephemeral lily Erythronium dens-canis combine red-brown anthocyanin patches with silvery-grey flecks caused by subepidermal air spaces; the brown coloration is resorbed within weeks of emergence, earlier in non-flowering than in flowering plants. Photoprotection has been ruled out, and correlative evidence now points toward camouflage against herbivores rather than pollinator attraction, but the adaptive function has never been established by direct experiment, and neither the developmental mechanism that builds the air spaces nor the regulation and ecological cost–benefit balance of the transient pigmentation has been investigated in this species. This record states that problem — the experimental determination of what the mottling is for, how it is built, and what it costs — in the open form left by the literature through 2026.

Background

Erythronium dens-canis L. (dogtooth violet) is a spring ephemeral geophyte — an understory bulb plant of southern European deciduous forests that completes most of its aboveground life in the few weeks between snowmelt and canopy closure. Its leaves carry a striking, transient mottling: red-brown patches, produced by vacuolar anthocyanins (water-soluble red–purple pigments) confined to a single uppermost subepidermal layer of photosynthetic cells, together with permanent silvery-grey flecks. La Rocca et al. (2014) showed that the silvery flecks are caused by air spaces between the upper epidermis and the underlying cell layer, formed by inward (downward) bulges of epidermal cells — a construction Zhang et al. (2020) classify as Type II, or air-space-type, leaf variegation, which their survey of 1,710 variegated species identifies as the most common variegation mechanism (about 56% of species). A 1957 anatomical study of the Asian congener E. japonicum, cited within La Rocca et al. (2014), had already attributed silvery flecks to intercellular air spaces, but the developmental cues that make epidermal cells bulge inward in a spatially patterned way remain unknown. The brown component of the mottling is transient: anthocyanin is resorbed within a few weeks of leaf emergence, earlier in non-flowering plants than in flowering plants, in which resorption accelerates only after the young fruits have developed. Several functional hypotheses for such mottling in spring forest herbs have been debated since Givnish (1990) proposed that leaf mottling acts as camouflage, disguising nutrient-rich young leaves against the dappled, leaf-littered forest floor and disrupting their outline for visually foraging herbivores. An alternative is that the reflective silvery flecks act as a visual signal to pollinating insects; a third, that anthocyanins provide photoprotection against high spring light before canopy closure. The photoprotective hypothesis is effectively closed for this species: Esteban et al. (2008) found that red patches of E. dens-canis show greater, not lesser, loss of photosystem II efficiency (photosystem II, PSII, being the light-driven reaction centre of photosynthesis) under light stress, and La Rocca et al. (2014) found photosynthetic pigments, chloroplast ultrastructure, and chlorophyll-fluorescence parameters — chlorophyll fluorescence being a non-invasive optical probe of photosynthetic performance — virtually identical between anthocyanin-containing and anthocyanin-free areas, with pigment disappearing before canopy closure when light is still highest. What remains unresolved is everything else: which of the surviving hypotheses the mottling actually serves, how the air-space pattern is developmentally constructed, why resorption timing depends on reproductive status, and what the transient pigmentation costs and returns in carbon, nitrogen, and energy. Pupillo and Astuti (2017), studying a population of the same species in the same northern-Apennine region near Bologna, showed that the leaf-background pattern type (silvery, silvery-and-green, green) is phenotypically stable within individuals across years and argued from the discoloration time-course that the mottling's role is unlikely to be pollinator attraction, possibly camouflage; Kiel (2026), using community-science photographs of five North American Erythronium species, found that mottling texture increases with forest canopy cover and deer abundance, a correlative signature consistent with the Givnish camouflage hypothesis — but that study did not include E. dens-canis and involved no manipulation of leaves or measurement of actual herbivory on them. Across other variegated genera the adaptive question remains contested: Sullivan and Koski (2024) found no difference in herbivory between variegated and plain-leaved Hexastylis plants and instead supported an abiotic (temperature and light) association, while Niu et al. (2014) demonstrated in the alpine plant Corydalis benecincta how a decisive test can be run — modelling leaf-versus-background discriminability for the relevant herbivore vision system, then measuring herbivore damage, survivorship, photosynthetic cost, and mating opportunity across color morphs.

Problem Statement

Determine, by direct evidence rather than correlative inference, the biological significance of the transient leaf mottling of Erythronium dens-canis. The problem has one overarching objective — to explain why this striking, patterned, and ephemeral coloration exists and how it is built — and four aspects of that objective remain unresolved for this species: (1) identify the adaptive function of the mottling experimentally, deciding among camouflage against visually foraging herbivores on the leaf-litter background (the Givnish hypothesis), a pollinator-attracting visual signal from the reflective silvery flecks, a combination of both, or neither — for example by measuring herbivore damage and pollinator visitation on naturally mottled leaves versus leaves whose pattern has been experimentally removed or altered (e.g., artificially degreened or repainted leaves), with appropriate sham-manipulated controls; (2) identify the developmental mechanism that constructs the subepidermal air spaces under the silvery flecks, i.e., the cues by which patches of upper epidermal cells form their inward bulges and the interface between the epidermis and the underlying photosynthetic cell layer (the chlorenchyma) separates in a spatially patterned way; (3) identify the regulatory basis — hormonal, source–sink (the balance between photosynthate-exporting and photosynthate-importing tissues), or reproductive-status-linked — and the functional significance of the earlier anthocyanin resorption in non-flowering relative to flowering plants, which La Rocca et al. (2014) showed accelerates only after fruit development; and (4) quantify the ecological costs and benefits of the transient pigmentation pattern in carbon, nitrogen, and energy budgets. These four aspects are jointly required to resolve the objective and each can be investigated independently: a complete answer must address all four for E. dens-canis by direct evidence, whereas any single aspect answered on its own — however decisive — counts only as a partial resolution. The question concerns E. dens-canis in its natural populations; its findings may then be compared with those for other Erythronium species and other spring ephemerals with transient foliar pigmentation.

References

  1. La Rocca N., Pupillo P., Puppi G., Rascio N. (2014). Erythronium dens-canis L. (Liliaceae): An unusual case of change of leaf mottling. Plant Physiology and Biochemistry 74: 108–117. DOI 10.1016/j.plaphy.2013.11.005. https://doi.org/10.1016/j.plaphy.2013.11.005
  2. Esteban R., Fernández-Marín B., Becerril J.M., García-Plazaola J.I. (2008). Photoprotective implications of leaf variegation in E. dens-canis L. and P. officinalis L. Journal of Plant Physiology 165(12): 1255–1263. DOI 10.1016/j.jplph.2007.07.024. https://doi.org/10.1016/j.jplph.2007.07.024
  3. Givnish T.J. (1990). Leaf mottling: relation to growth form and leaf phenology and possible role as camouflage. Functional Ecology 4: 463–474. DOI 10.2307/2389314. https://doi.org/10.2307/2389314
  4. Pupillo P., Astuti G. (2017). Population structure of Erythronium dens-canis L. (Liliaceae) in the northern Apennines (Italy). Italian Botanist 4: 1–14. DOI 10.3897/italianbotanist.4.12439. https://doi.org/10.3897/italianbotanist.4.12439
  5. Kiel N.G. (2026). Camouflage via leaf mottling among North American Erythronium species increases with forest cover and deer abundance. American Journal of Botany 113(6): e70208. DOI 10.1002/ajb2.70208. https://doi.org/10.1002/ajb2.70208
  6. Sullivan C.N., Koski M.H. (2024). An elevational cline in leaf variegation: Testing anti-herbivory and abiotic heterogeneity hypotheses in maintaining a polymorphism. American Journal of Botany 111(10): e16411. DOI 10.1002/ajb2.16411. https://doi.org/10.1002/ajb2.16411
  7. Niu Y., Chen G., Peng D., Song B., Yang Y., Li Z., Sun H. (2014). Grey leaves in an alpine plant: a cryptic colouration to avoid attack? New Phytologist 203: 953–963. DOI 10.1111/nph.12834. https://doi.org/10.1111/nph.12834
  8. Zhang J.-H., Zeng J., Wang X., Chen S.-F., Albach D., Li H.-Q. (2020). A revised classification of leaf variegation types. Flora 272: 151703. DOI 10.1016/j.flora.2020.151703. https://doi.org/10.1016/j.flora.2020.151703
  9. Zhang J., Li J., Zou L., Li H. (2022). Transcriptome Analysis of Air Space-Type Variegation Formation in Trifolium pratense. International Journal of Molecular Sciences 23(14): 7794. DOI 10.3390/ijms23147794. https://doi.org/10.3390/ijms23147794