related as shown in the cladogram below (based on Qiu et al. 2006 with additional names from Crane et al. 2004). Studies based on morphology rather than on genes and proteins have regularly reached different conclusions; for example that neither the monilophytes (ferns and horsetails) nor the gymnosperms are a natural or monophyletic group. There is considerable variation in how these relationships are converted into a formal classification. Consider the angiosperms or flowering plants. Many botanists, following Lindley in 1830, have treated the angiosperms as a division. Palaeobotanists have usually followed Banks in treating the tracheophytes or vascular plants as a division, so that the angiosperms become a class or even a subclass. Two very different systems are shown below. The classification on the left is a traditional one, in which ten living groups are treated as separate divisions; the classification on the right (based on Kenrick and Crane's 1997 treatment) sharply reduces the rank of groups such as the flowering plants. (More complex classifications are needed if extinct plants are included.) An updated phylogeny of Embryophytes based on the work by Novíkov & Barabaš-Krasni 2015 and Hao and Xue 2013 with plant taxon authors from Anderson, Anderson & Cleal 2007 and some clade names from Pelletier 2012 and others. Puttick et al./Nishiyama et al are used for the basal clades. Diversity Bryophytes Bryophytes consist of all non-vascular land plants (embryophytes without vascular tissue). All are relatively small and are usually confined to environments that are humid or at least seasonally moist. They are limited by their reliance on water needed to disperse their gametes, although only a few bryophytes are truly aquatic. Most species are tropical, but there are many arctic species as well. They may locally dominate the ground cover in tundra and Arctic–alpine habitats or the epiphyte flora in rain forest habitats. The three living divisions are the mosses (Bryophyta), hornworts (Anthocerotophyta), and liverworts (Marchantiophyta). Originally, these three groups were included together as classes within the single division Bryophyta. They have usually been placed separately into three divisions under the assumption that the bryophytes are a paraphyletic (more than one lineage) group, but newer research supports the monophyletic (having a common ancestor) model. The three bryophyte groups form an evolutionary grade of those land plants that are not vascular. Some closely related green algae are also non-vascular, but are not considered "land plants". Marchantiophyta (liverworts) Bryophyta (mosses)