Most references have a slightly different classification system.
4.Porphyrion small, leathery evergreen leaves, often prostrate stems 5.Robertsoniana evergreen, above- ground stolons, leathery basal rosettes 6. Diptera hairy with runners, rounded leaves, summer or fall bloom, likes humus soil 7. Nephrophyllum usually biennial, reniform leaves toothed or divided 8. Trachyphyllum evergreen, grass-like cushions, leaves simple 9. Xanthizoon evergreen, mats or cushions, alternate fleshy leaves lime encrusted 10.