A Vogel spiral is a discrete arrangement of points whose polar coordinates are
 |  |  |
(1)
|
 |  |  |
(2)
|
where 
, 
, and 
is a fixed divergence angle
(Vogel 1979). The customary choice 
is the golden
angle and produces the interlacing spiral patterns
used to model phyllotaxis in sunflower heads.
The radii satisfy the equation of Fermat's spiral, but a Vogel spiral is a discrete point set rather than a continuous plane curve.
Akiyama (2020) proved that a Vogel spiral is a Delone set iff the turn fraction 
is badly approximable,
meaning that it is an irrational number whose
continued fraction terms are bounded.
In particular, the golden angle gives a Delone
set.
A daisy similarly produces a flower-like family of visible spirals by placing repeated shapes along a spiral, but it generally uses different radial scaling.
This model of a sunflower head is distinct from a sunflower in combinatorics.
