The Amaranthaceae s.str. comprise about 1000 species in approx. 70 genera and are of mainly tropical distribution. Within Caryophyllales, the family forms a monophyletic group with the Chenopodiaceae (1400 spp. in approx. 100 genera, predominantly occurring in temperate regions of both hemispheres). This clade also has been classified as Amaranthaceae s.l.. Pollen morphology in Amaranthaceae is extremely diverse and features such as stellate pore ornamentation are found nowhere else among angiosperms. The complete chloroplast trnK intron (including matK, 2700 characters) was sequenced for all major groups in Amaranthaceae s.str., for representatives from Chenopodiaceae, and allied caryophyllid families. Parsimony and Likelihood analyses revealed that Amaranthaceae s.str. are monophyletic, and that subfamily Amaranthoideae (characterized by 4-locellate anthers) is paraphyletic to the bilocellate Gomphrenoideae. In Amaranthoideae, the tribe Celosieae (with the ornamental Celosia) is monophyletic, while the Amarantheae (including the grain amaranths) are polyphyletic. Thus, the ovule number as traditionally used to delimitate both tribes appears homoplastic. Moreover, the currently accepted subtribal classification does not reflect natural groups. SEM study of almost all genera of Amaranthaceae s.str. (totalling 25% of the species) and selected Chenopodiaceae yielded 25 pollen characters. Ancestral states were reconstructed on the molecular phylogeny. According to this analysis, spheroidal, pantoporate pollen with flat mesoporia and subglobose ektexinous bodies that are evenly spread on the aperture membrane is plesiomorphic. Hook-shaped and stellately arranged ektexinous bodies (stellate pore ornamentation) appear to have evolved at least twice. In Gomphrenoideae, metareticulate pollen (meshes of the reticulum homologous to mesoporia) is a synapomorphy for the terminal genera. In Amarathaceae pollen characters proved to be highly informative, and synapomorphic for clades at different levels.

Key words: Amaranthaceae, electron microscopy, matK, phylogeny, pollen, trnK