Delimitation of Amaranthus cruentus L. and Amaranthus caudatus L. using micromorphology and AFLP analysis: an application in germplasm identification M. Costea 1, *, D.M. Brenner 2 , F.J. Tardif 3 , Y.F. Tan 4 and M. Sun 4 1 Department of Biology, Wilfrid Laurier University, 75 University Avenue West, Waterloo, ON, N2L3C5, Canada; 2 Department of Agronomy, Plant Introduction Station, Iowa State University, Ames, IA 50011- 1170, USA; 3 Department of Plant Agriculture, University of Guelph, Guelph, ON, N1G2W1, Canada; 4 Departments of Botany and Zoology, The University of Hong Kong, Hong Kong; *Author for correspondence (e-mail: mcostea@wlu.ca; phone:+519-884-0710; fax:+519-746-0677) Received 25 January 2005; accepted in revised form 19 June 2005 Key words: AFLP, Amaranthus caudatus, Amaranthus cruentus, Germplasm identification, Grain ama- ranths, Micromorphology Abstract The ‘Morelos’ accessions of Amaranthus from Mexico demonstrate taxonomic ambiguity at the basic morphologic level. The main cause is the enormous morphological and genetic variation exhibited by the species in the genus. Although basic morphological criteria can be applied to herbarium specimens or germplasm collections for quick taxonomic identification, the morphological data alone can be misleading. To ascertain the taxonomic identity of the ‘Morelos’ accessions and their hypothesized species affiliation to Amaranthus caudatus or Amaranthus cruentus, we conducted a comparative analysis of phylogenetic rela- tionships among these taxa/accessions using amplified fragment length polymorphism (AFLP) and micromorphology methods. Based on AFLP data, all the controversial ‘Morelos’ accessions can be con- sistently placed into a single A. cruentus species clade, which is clearly separated from the A. caudatus species clade. The AFLP-based phylogenetic relationship of ‘Morelos’ and delimitation of A. cruentus and A. caudatus are further supported by micromorphology, showing that the combination of these techniques can provide more reliable data for germplasm identification than each method used alone. Abbreviations: AFLP – amplified fragment-length polymorphism; RAPD – randomly amplified polymor- phic DNA; RFLP – restriction fragment length polymorphism; SEM – scanning electron microscopy Introduction Three ancient cereal Amaranthus species, A. cau- datus L., A. cruentus L. and A. hypochondriacus L., are nowadays studied and cultivated worldwide because of their exceptional nutritional value of both seeds and leaves (Brenner et al. 2000). Addi- tionally, the species are widespread ornamentals and they have a potential as forage crops and as a source of red food colorants (Cai et al. 1998). Studying the herbarium specimens held in the National Arboretum (NA) and the corresponding Genetic Resources and Crop Evolution (2006) 53:1625–1633 Ó Springer 2006 DOI 10.1007/s10722-005-0036-3