RELATIONSHIPS IN THE CARYOPHYLLALES AS SUGGESTED BY PHYLOGENETIC ANALYSES OF PARTIAL CHLOROPLAST DNA ORF2280 HOMOLOG SEQUENCES

Phylogenetic relationships within the angiosperm order Caryophyllales were investigated by comparative sequencing of two portions of the hig hly conserved inverted repeat (totaling some 1100 base pairs) coincidi ng with the region occupied by ORF2280 in Nicotiana, the largest gene in the plastid genomes of most land plants. Data were obtained for 33 species in 11 families within the order and for one species each of Pl umbaginaceae, Polygonaceae, and Nepenthaceae. These data, when analyze d along with previously published ORF (open reading frame) sequences f rom Nicotiana, Spinacia, Epifagus, and Pelargonium using parsimony, ne ighbor-joining, and maximum likelihood methods, reveal that: (1) Amara nthus, Celosia, and Froelichia (all Amaranthaceae) do not comprise a m onophyletic group; (2) Amaranthus may be nested within a paraphyletic Chenopodiaceae; (3) Sarcobatus (Chenopodiaceae) is allied with Nyctagi naceae + Phytolaccaceae (the latter family excluding Stegnosperma but including Petiveria); and (4) Caryophyllaceae (with Corrigiola basal w ithin the clade) are sister group to Chenopodiaceae + Amaranthaceae. B asal relations within the order remain obscure. Sequence divergence va lues in pairwise comparisons across all Caryophyllales taxa ranged fro m 0.1 to 5% of nucleotides. However, despite these low values, 23 inse rtion and deletion events were apparent, of which five were informativ e phylogenetically and bolstered several of the relationships listed a bove. A polymerase chain reaction (PCR) survey for ORF homolog length variants in representatives from 70 additional angiosperm families rev ealed major deletions, of approximate to 100 to 1400 base pairs, in 19 of these families. Although the ORF is located within the mutationall y retarded inverted repeat region of most angiosperm chloroplast DNAs, this gene appears particularly prone to length mutation.