A cladistic analysis of Atripliceae (Chenopodiaceae) based on morphological data

Although there is considerable controversy regarding the phylogenetic struc ture and infrafamilial classification of Chenopodiaceae, the tribe Atriplic eae generally has been recognized as a natural group. Relationships within this tribe remain controversial, especially with regard to the taxonomic de limitation and infrageneric classification of the largest genus, Atriplex. Most of the genera that have been segregated from Atriplex are monotypic or include few species that are variously distributed in Africa. Australia, o r North America: however, one of these genera, Obione, includes half of all species of Atriplex sens. lat., and has a worldwide distribution. Seventy terminals were included in a cladistic analysis, based on morphological cha racters, to test the monophyly of Atripliceae and its subtribes, and of Atr iplex, Obione, and several infrageneric groups. The taxonomic sample includ es representatives of 22 putative genera of the tribe Atripliceae, and all sections of Atriplex (except Austrobione) and Obione, following Ulbrich's ( 1934) classification, from throughout the geographic range of the tribe. Pr imary hypotheses of homology were postulated for 78 characters reflecting v ariation in gross morphology, leaf anatomy, and chromosome number. Results, as reflected in the strict consensus tree, suggest that both Atripliceae a nd Atriplex are paraphyletic, with three outgroup genera from tribe Chenopo dieae (Chenopodium, Monolepis, and Suckleya) nested among species of Atripl ex. Also, monophyly of the subtribes of Atripliceae is not supported. The r esults suggest that the deepest branch within Atripliceae is between Cerato carpus and all other members of the tribe. Kruscheninnikovia, the next genu s to diverge, is the sister of a diverse clade that consists of two subclad es. One of these includes Theleophyton plus Endolepis, Zuckia, and Gravia, and the other includes all species of Atriplex in the sample, plus all samp led species of Obione, the remaining genera of Atripliceae, and the three s ampled genera of Chenopodieae, with Halimione pedunculata as the sister of all other members of this clade. Resolution generally is poor among species of Atriplex, and neither Obione nor most of the sections of Atriplex is re solved as monophyletic, though there is support for the monophyly of sectio n Spongiocarpus. Also nested among species of Atriplex and Obione is a well resolved clade with four defined subgroups: Suckleya by itself, Atriplex h ortensis and Chenopodium; Archiatriplex, Axyris, and Microgynoecium; and Mo nolepis, Proatriplex, Manochlamys, and Exomis. The results support the reco gnition of Endolepis, Theleophyton, and Zuckia (sensu Standley 1915) as seg regates of Atriplex, but not Blackiella, Hatimione, Haloxanthium, Morrisiel la, Neopreissia, Obione, Pachypharynx, or Senniella. In addition, the resul ts suggest that the continued recognition of Archiatriplex, Axyris, Exomis, Manochlamys, Microgynoecium, Proatripex, and Spinacia (Atripliceae), as we ll as Chenopodium. Suckleya, and Monolepis (Chenopodieae) should be reconsi dered. If these results are confirmed by further analyses using other chara cter sets and a wider taxonomic sample, it will be necessary either to tran sfer several genera to Atriplex or to circumscribe Atriplex narrowly. and s egregate a number of additional genera from it.