The genus Micranthes (Saxifragaceae)

Micranthes oreganaMeyers, California

I. Organism

The genus Micranthes (Saxifragaceae) is found primarily in temperate, Arctic, and alpine regions. Micranthes is one of the largest genera in Saxifragaceae with ~75 species, and the highest diversity of taxa is found in North America[1,2]. Species span from sea level in northern latitudes (e.g., M. nudicaulis) to 5300 m in the Himalayas (e.g., M. melanocentra)[2,3]. Some plants are narrow endemics (e.g., M. eriophora) while others are circumpolar (e.g., M. nelsoniana)[4]. Micranthes shows a wide range of ecological diversity; I have collected them in varied habitats including the highest peaks of the Sierra Nevada, sub-tropical forests of China, the deciduous woodlands of Missouri, and the desert mountains of Arizona. This ecological diversity is reflected in the morphological variation seen within Micranthes and many of the traits associated with certain taxa are indicative of its habitat (e.g., densely hairy plants in cold habitats). 


Micranthes melanocentra, Sichuan, China


The full potential of this group for answering significant evolutionary questions has not been achieved in the past. This is in part because previous phylogenetic research has been plagued by poor phylogenetic resolution and low internal support, likely reflecting recent, rapid radiation. Previous studies employed too few genes and limited taxon sampling, without investigation into probable underlying phylogenetic conflicts (e.g., hybridization) [1,5-7]. Additionally, it has previously been speculated that hybridization has been a driving force of speciation in this group reflected in a wide range of reported chromosome counts and incongruent placements in previous studies [1,2,4,8] However, through our first round of high-throughput sequencing—targeting 596 putatively single copy nuclear genes and 88 plastid genes and spacers, and greatly increased taxon sampling—we have established a much-improved phylogenetic framework. 

Micranthes rufidula, Cone Mtn, ORegon

III. Taxonomy

In the most comprehensive look at the group, Webb and Gornall (1989) remarked that Micranthes is the “largest and potentially most confusing group of saxifrages.” This is largely attributable to the extreme locations of many species and rampant putative hybridization. The taxonomic history of this group is, at best, convuluted. Between being incorrectly subsumed under the wrong genus (i.e., Saxifraga) for almost a century to vast confusion about specific epithets, teasing apart the true taxonomy of this group is a task all of itself. There have been many days when I have found myself reading early 20th century botanical literature in Latin or German looking for the ever elusive basionym. Luckily, I enjoy this kind of thing and have been able to develop these skills working on treatments for both the Flora of North America and a revision of Cronquist's Manual of the Vascular Plants of Northeastern United States and Adjacent Canada.