Open Questions
Unresolved problems in phyllotaxis research, based on modern literature from 2000–2024. These questions span biology, physics, mathematics, and developmental modeling.
1Why do Fibonacci spirals dominate in plant phyllotaxis?
Despite physical and developmental models reproducing Fibonacci spirals, it remains unclear whether their evolutionary dominance is due to adaptive advantage or developmental constraints.
Kitazawa & Fujimoto (2015) — A Dynamical Model for Phyllotactic Pattern Formation (PNAS)
2Why are only a few phyllotactic modes realized in nature?
Many mathematically valid patterns exist, but plants overwhelmingly adopt just a small subset. The constraints (genetic, mechanical, or evolutionary) that eliminate others are not fully understood.
Atela et al. (2002) — The geometric and dynamic origins of phyllotaxis (Journal of Theoretical Biology)
3How do plants regenerate phyllotactic order after meristem injury?
Plants can re-establish spiral patterns after damage, but the molecular and mechanical cues that reset phyllotaxis remain elusive.
Landrein et al. (2015) — Mechanical stress contributes to organ initiation (Cell Reports)
4How does a single apical cell generate spiral order in mosses?
In bryophytes, a single cell produces spiral patterns without multicellular gradients. The mechanism is unknown.
Coudert et al. (2017) — Three ancient hormonal cues coordinate shoot branching (Nature Plants)
5How do spiral and whorled phyllotaxis switch during evolution?
It's unclear how spiral, decussate, and whorled modes interconvert developmentally, or which floral phyllotaxis was ancestral.
Chanderbali et al. (2010) — What is the origin of the flower? (New Phytologist)
6Is auxin sufficient, or do other signals drive phyllotaxis?
Auxin transport models explain much, but roles of other hormones (e.g. cytokinin, brassinosteroids) remain poorly integrated.
Besnard et al. (2014) — Cytokinin signalling controls phyllotaxis (PNAS)
7How are surface patterning and vascular connection coordinated?
Auxin convergence at the surface triggers primordia, but how this is synchronized with inner tissue canalization (vein initiation) is not fully resolved.
Hartmann et al. (2019) — A phyllotaxis model integrates transport and growth (PNAS)
8How do mechanical forces influence phyllotactic patterning?
Tissue stress alters PIN1 polarity and auxin flow. The interplay between mechanical deformation and pattern emergence is not fully mapped.
Nakayama et al. (2012) — Mechanical regulation of auxin transport (Current Biology)
9What stabilizes pattern selection against noise?
Even under molecular or positional noise, Fibonacci spirals remain robust. The mechanism stabilizing regime selection is unclear.
Refahi et al. (2016) — A stochastic multicellular model identifies watermarks of organ initiation (eLife)
10Can rare patterns like spiromonostichy be explained?
Extreme spiral geometries (e.g. in Costus) don't fit classical inhibitory-field models. Recent work suggests combining inhibitory and inductive effects.
Yonekura et al. (2024) — A new model of phyllotaxis to solve spiromonostichy (Journal of Theoretical Biology)