Ambrosia chamissonis Asteraceae

The morphological variation within the complex is reflected in the number of taxonomic descriptions (ca. 20) that have been published defining species, subspecies. 

The Geography of Phytochemical Races, Springer Science+Business Media B.V. 2009 

Although these data suggest relationships, clear-cut phylogenetic connections among the various populations must await the application of macromolecular techniques. In addition to providing insight into the evolutionary relationships, such data would also likely provide an idea of when colonization might have occurred. 

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