How do I graph a 30-petal rhodonea curve (rose)?

Question

A rose of the form $r = \cos(c\theta)$ normally has $2c$ petals when $c$ is even and $c$ petals when $c$ is odd.
A rose may also have $4c$ petals when $c$ can be expressed as $Z + \frac{1}{2}$ where $Z$ is an integer.
A rose may also have $12c$ petals when $c$ can be expressed as $Z \pm \frac{1}{6}$.
A rose may also have as many petals as one with $3c$ when $c$ can be expressed as $\frac{Q}{3}$ but not as $Z$ where $Q$ is either $Z$ or $\frac{Q}{3}$.
How is a rose with 30 petals graphed (in the form shown above)?