Daisy, I found an old post on Dave's Garden that may help you ID your plant if you're into counting spines etc.
On Mar 17, 2005, Xenomorf from Phoenix, AZ (Zone 9b) wrote:
The differences between the subspecies are:
--ssp. karwinskiana; has medium yellow flowers with purpleish midviens; No central spines and 6 radial spines.
--ssp. collinsii; has white flowers with deeper pinkish midveins; One central spine and 7 radial spines.
--ssp. beiselii; has white flowers with red tinted midveins; One central spine and 5-8 radial spines.
--ssp. nejapensis; also has white flowers with red tinted midveins, but the spines are larger and white and has much more wool; No central spines and 3-5 radial spines per areole.
Note that subsp collinsii is recognized in the COL as M. voburnensis subsp collinsii (Britton and Rose) U. Guzman and that even the experts can get it wrong as shown below. Look how many times Britton and Rose had their original description and name changed as new info came about.
Mammillaria karwinskiana subs. collinsii (Britton & Rose) D.R.Hunt
Mammillaria collinsii (Britton & Rose) Orcutt
Mammillaria voburnensis subs. collinsii (Britton & Rose) U.Guzmán
Mammillaria voburnensis var. collinsii (Britton & Rose) Repp.
Neomammillaria collinsii Britton & Rose
One last comment, your plant is beautiful and well grown!
