An understanding of cold tolerance and intolerance in plants is becoming increasingly important as global climate change causes weather patterns to shift and extreme temperatures to become a more common occurrence. To further understand the genetic basis for cold intolerance phylogenetic relationships between species of cold intolerant yucca were investigated through DNA sequence comparison and cold tolerance testing. Over the course of 7 weeks, chloroplast DNA extractions were performed on 11 species of cold tolerant and cold intolerant yucca, followed by polymerase chain reaction (PCR) amplification of the trnT-trnL intergenic spacer non-coding region and the intergenic spacer region (ITS). The regions of amplified DNA were then sequenced and the nucleotide sequences of each yucca species compared, revealing the locations of base mutations and the percent similarity between species. Tissue heat and cold tolerance was then investigated in 6 of the cold intolerant yucca species using vital staining to detect living cells. With the successful gene amplification of a greater number of yucca species it will be possible to employ the phylogenetically independent contrast (PIC) method and develop a phylogenetic tree based on nucleotide sequences in conjugation with cold tolerance data and leaf and root characteristics. The phylogeny will offer insight into the evolution and speciation of yuccas and the development of cold tolerance as well as other potentially adaptive traits.