In my last post I offered a brief introduction to Abronia biogeography, and highlighted some of the problems facing those who study this group. Here, I’d like present the interesting case of A. matudai and A. smithi. My hope is to draw some attention to an overlooked taxonomic quandry, and perhaps stimulate readers to consider Abronia for their future work in Mexico!
Both A. matudai and A. smithi are chronically understudied. They are endemic to the Sierra Madre de Chiapas mountains, and each is known from fewer than 10 localities rangewide. Both exemplify the archetypal dragon-like image that people sometimes associate with Abronia—bright green in color and often with enlarged supra-auricular scales or “horns” behind their ears. Although based strictly on morphological evidence (published DNA sequence data is available only for A. matudai), both are considered members of the Auriculabronia clade. This is one of six currently recognized groups within the genus.
Perhaps the most obvious external difference separating these two species is that A. smithi has dramatic spine-like supra-auricular scales, while in A. matudai the supra-auriculars are only somewhat protuberant and not pointed like spines. A handful of other external features separate them, but it could be argued that these two taxa are not strongly differentiated morphologically. In their classic monograph published a quarter-century ago, Drs. Jonathan Campbell and Darrel Frost first elevated A. smithi from within A. ochoterenai (a story for another day!). Those authors examined a total of ten A. smithi specimens and four A. matudai specimens in making their taxonomic determination. Since then, novel material attributed to both species has trickled into a few museums, but no detailed data on these specimens has ever been published. It is thus an open question whether analysis of this new material would support, or soften, the presumed morphological divergence between these two taxa. Based on my collaborative recent work with other members of the genus, the latter option might be more likely.
A close look at regional geography raises further questions. Currently, A. matudai is known to occupy an elevational range of ca. 1540–2700 m, while A. smithi is reported from 1580–2800 m elevation. Both species inhabit “cloud forest,” a rather nebulous term that can encompass a wide diversity of forest types. While perhaps an oversimplification given that elevation is not a perfect proxy for Abronia habitat, one might reasonably assume the existence of a low-elevation barrier to dispersal between these two taxa. The deep entrenchments of the Río Coatan and Río Huixtla, at first glance, appear to fit the bill. However, in reality a narrow montane corridor in excess of 1900 m spans the headwaters of these rivers, connecting the escarpments occupied by A. matudai to the east and A. smithi to the west. As such, there is no obvious geographic barrier to gene flow.
So, is A. smithi valid? Or could it perhaps represent a clinal extreme of A. matudai? And could there be one or more cryptic, undescribed lineages clouding the issue?
Just some of the many Abronia questions waiting to be answered…please comment below with any feedback!
Biology of Mexican Herps 
I’ve wondered this about a few anguid taxa, especially given their propensity for ridiculous morphological variation. When taxonomic decisions are based on such limited sampling then it must be very difficult to come to a firm conclusion on taxonomic status.
I look forward to hearing more about Abronia ochoterenai (and A. leurolepis if you’re up for it) in the future. Based on my (dated) investigations, there were a lot of open questions as to their validity and even whether the localities from the descriptions were accurate. Those problems are a tough hurdle to resolve.
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Yes, Campbell and Frost were laudably open and transparent about how their taxonomic decisions (including their recognition of A. ochoterenai and A. leurolepis) were based on limited material—a problem that plagues virtually all Abronia research. But they put forward clear and testable taxonomic hypotheses. My intent with this post is to emphasize that no taxonomy is written in stone, and also to offer a reminder that as new material becomes available for understudied taxa, it creates an opportunity to revisit prior taxonomic decisions. This is something that I find quite enjoyable and fulfilling about working in Mexico: serendipitous sampling of little-known species can, when properly contextualized, lead to substantive advances in our understanding of diversity and natural history.
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Let us know where to send the tissue! You’re likely right on matudai and smithi.
We followed a similar train of thought with A. ochoterenai, and stopped short of writing up a rediscovery/redescription as the extent of the taxonomic disaster came into focus. Good luck!
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Thanks!
If high-quality collection data is available for each sample, including accurate GPS coordinates, then I imagine Dr. Adrián Nieto-Montes de Oca and the MZFC-HE would gratefully accept the Abronia material you have.
Bummer about the A. ochoterenai situation. Because I have seen the social media announcements of a rediscovery of A. ochoterenai, I was hoping that a formal publication was in the works with details regarding its distinctiveness from A. lythrochila (or lack thereof).
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