Caudiciforms are not related, they just kind of look alike. They have been formed by nature within many different families. Changes in the taxonomy have been made through time, and with the DNA mapping, the latest system is PPG I for the spore-plants, just like APG IV 2016 is for the Angiosperms; the flowering plants. The rest is the Gymnosperm; the Naked Seed plants, also called Acrogymnospermae.
These plants are the last surviving of ancient families, and their relations are more clear, than the recent developed species. To my knowledge, not much  DNA mapping have been spend on them. Never the less, I have made a new sheet with the general structure and made link to the families with caudiciform members: Cupressaceae, Cycadaceae, Ginkgoaceae, Welwitschiaceae and Zamiaceae.
Gymnosperms are a group of plants which produce seeds that are not contained within an ovary or fruit. All of the Spermatophytes except the Magnoliophyta.