Final answer:
The best method to determine if two plant species share a recent common ancestor is by comparing 1) DNA sequences. Sequence homology and the use of molecular clocks offer a precise approach to establish relatedness and evolutionary timelines, supported by both morphological and molecular evidence.
Step-by-step explanation:
To determine whether two plant species share a recent common ancestor, examining DNA sequences is the most effective method. Sophisticated computational tools and databases like GenBank enable scientists to compare DNA sequences to estimate the evolutionary distance and time elapsed since a common ancestor was shared. This approach, referred to as molecular phylogenetics, looks at the percentage of sequence identity or homology. Sequence homology reflects shared evolutionary pathways, a concept substantiated by the observation that organisms with more similar DNA are typically more closely related.
When it comes to identifying similarities between species, morphologic and molecular evidence are critical. Homologous structures, which are physical features that share both morphological and genetic overlap, often indicate common ancestry. However, DNA analysis provides a clearer and more precise picture than morphological comparisons alone, especially with advancements in molecular biology and computational analysis. Moreover, molecular clocks, which use DNA sequence data to estimate relatedness and divergence times, augment the information from the fossil record to establish a more accurate evolutionary timeline.