Please refer to the diagram below. If we assume that the common ancestor of all living rubber boas is the dwarf form, then the umbratica lineage is morphologically closest to the ancestral form among all of the lineages of living rubber boas. The common ancestor of the Northwestern subclade and Sierra Nevada subclade is also likely to be the dwarf form, since the dwarf form is found in some populations of the Sierra Nevada subclade, and especially since these dwarf populations are also geographically closest to the San Bernardino Mountain populations of umbratica. This would be a classic case of budding evolution (or peripatric speciation), if the rubber boa lineages are considered different species. But since the dwarf form is part of the Sierra Nevada mtDNA lineage, splitting the species Charina bottae into two species would result in two morphologically undefinable species. Again, this is what the cladists are forced to recognize in order to practice Hennigian taxonomy.

The rubber boa appears to consist of an ancestral dwarf form which is found in southern California and in Kern County. A second geographic race of apparently derived large morph is found from coastal Monterey County north to Canada and east to Washington, Utah and states adjacent to these, but this race is absent from the Sierra Nevada range. A third race of large morph, which appears to have evolved independently of the coastal form, inhabits the Sierra Nevada range generally north of Kern County. There are no consistently definable morphological differences between the coastal and the Sierra Nevada races, except in their mtDNA. And the fact that they most likely evolved independently makes it untenable to consider them to be the same subspecies despite the fact they are both large morphs. Hence it is not possible to split C. bottae into a dwarf subspecies (or species) and a large morph subspecies (or species). Since there is also no evidence that any of these races are reproductively isolated from one another, it would be best to recognize but one species of rubber boa, without recognizing any subspecies.

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