Molecular and morphological evidence supports a new species in the genus Antiphytum from the Sierra Madre del Sur, in the state of Guerrero, Mexico, here described as A. brevicalyx. This species is unique in the genus by possessing a calyx shorter than the corolla tube at anthesis; it is similar to A. floribundum in inflorescence arrangement, but differs from that species in lacking a basal leaf rosette and having appendages on the corolla throat. According to phylogenetic analysis of nuclear ITS and plastid ndhF-rpl32 sequences representing seven of the eight North American species of the genus besides the proposed new species, accessions of A. brevicalyx form a well-defined clade within Antiphytum, corroborating its distinctive morphology. However, the analyses do not resolve the phylogenetic position of A. brevicalyx within the genus.

Total DNA was isolated from herbarium specimens or fresh leaves dried in silica gel for 53 accessions representing seven North American species of Antiphytum and seven accessions of the proposed new species. Sequences of the nuclear internal transcribed spacer (ITS) and the plastid ndhF-rpl32 spacer were amplified using the primer pairs ITS4 and ITS5 (White et al. 1990) and the newly designed primers rpl32.4R and ndhF.40R.Bor (GAAGTACGYTTTTTTGGAACTGC; ACATAGGAACTGTWAGTGGAAG), respectively. Sequence chromatograms were edited, assembled and manually aligned with PhyDE 0.9971 (Müller et al. 2010); SSRs and polynucleotide regions were annotated in both individual marker matrices and the corresponding aligned positions were used to label the base pair number(s) in the motif codifications. Gaps were coded using simple indel coding according to Simmons and Ochoterena (2000) and microstructural characters were coded according to Ochoterena (2009); both were added to the nucleotide concatenated matrix to build the final matrix for the analysis. The concatenated matrix was analyzed in WinClada to remove non-informative characters prior to analysis. Phylogenetic analyses were performed with the parsimony criterion using TNT 1.1 (Goloboff et al. 2000) alternating the four new technology search (NTS) strategies. The same procedure and analyses were also conducted for each locus separately.

For descriptive comparative purposes, distances among the concatenated sequences of the Antiphytum species were calculated as absolute nucleotide differences using PAUP 4.0a165 (Swofford 2003).