The following program is hopefully self-explanatory.
import pylab
# Number seeds in the sunflower seedhead
n = 200
# The golden ratio, 1.61803398874989...
phi = (1 + pylab.sqrt(5))/2
# Calculate and plot the seed positions, (r, theta) for each seed, s
s = pylab.linspace(0,n-1,n)
r = pylab.sqrt(s)
theta = 2 * pylab.pi * s / phi
pylab.polar(theta, r, marker='o', linestyle='', markersize=12, color='r')
pylab.show()