Taylor et al. in their book Paleobotany use Rhyniophyta as a formal taxon, but with a loose definition: plants "characterized by dichotomously branched, naked aerial axes with terminal sporangia". They thus include under "other rhyniophytes" plants apparently without vascular tissue. In 2010, the name paratracheophytes was suggested, to distinguish such plants from 'true' tracheophytes or eutracheophytes. In 2013, Hao and Xue returned to the earlier definition. Their class Rhyniopsida (rhyniopsids) is defined by the presence of sporangia that terminate isotomous branching systems (i.e. the plants have branching patterns in which the branches are equally sized, rather than one branch dominating, like the trunk of a tree). The shape and symmetry of the sporangia was then used to divide up the group. Rhynialeans (order Rhyniales), such as Rhynia gwynne-vaughanii, Stockmansella and Huvenia, had radially symmetrical sporangia that were longer than wide and possessed vascular tissue with S-type tracheids. Cooksonioids, such as Cooksonia pertoni, C. paranensis and C. hemisphaerica, had radially symmetrical or trumpet-shaped sporangia, without clear evidence of vascular tissue. Renalioids, such as Aberlemnia, Cooksonia crassiparietilis and Renalia had bilaterally symmetrical sporangia and protosteles. Taxonomy There is no agreement on the formal classification to be used for the rhyniophytes. The following are some of the names which may be used: Division Rhyniophyta Subdivision Rhyniophytina Banks (1968) Class Rhyniopsida Kryshtofovich (1925) Order Rhyniales Němejc (1950) Family Rhyniaceae Kidston & Lang (1920) Phylogeny In 2004, Crane et al. published a cladogram for the polysporangiophytes in which the Rhyniaceae are shown as the sister group of all other tracheophytes (vascular plants). Some other former "rhyniophytes", such as Horneophyton and Aglaophyton, are placed outside the tracheophyte clade, as they did not possess true vascular tissue (in particular did not have tracheids). However, both Horneophyton and Aglaophyton have been tentatively classified as tracheophytes in at least one recent cladistic analysis of Early Devonian land plants. Partial cladogram by Crane et al. including the more certain rhyniophytes: (See the Polysporangiophyte article for the expanded cladogram.) Genera The taxon and informal terms corresponding to it have been used in different ways. Hao and Xue in 2013 circumscribed their Rhyniopsida quite broadly, dividing it into rhynialeans, cooksonioids and renalioids. Genera included by Hao and Xue are listed below, with assignments to their three subgroups where these are given. Aberlemnia (renalioids) Aglaophyton (rhynialeans) Caia Cooksonia (cooksonioids + renalioids) Culullitheca Eogaspesiea (= Eogaspesia) (rhynialeans) Eorhynia Filiformorama Fusitheca (= Fusiformitheca) Grisellatheca Hsua