Resolving taxonomic complexity in the genus Boechera (Brassicaceae) using the Boechera Microsatellite Website: a case...

The genus Boechera (rock cress) comprises ∼75 sexual diploid taxa and >355 genetically distinct hybrid lineages, many of which reproduce asexually through apomixis. This complex reproductive landscape poses substantial challenges for taxonomy, similar to those encountered in genera such as Taraxacum, Hieracium, Poa and Rubus. The Boechera Microsatellite Website (BMW) offers an extensive database and analytical tools that are proving instrumental in resolving these difficulties. Here, we demonstrate the utility of the BMW through analysis of Boechera bodiensis, a rare and poorly understood species endemic to the western Great Basin of the USA.

First described as Arabis bodiensis by Rollins in 1982, this taxon is sparsely represented in herbaria and has long been considered a candidate for protection under the Endangered Species Act. However, its taxonomic identity has remained uncertain owing to morphological similarities with other 'Arabis' (Boechera) taxa. We integrate microsatellite DNA data from the BMW with morphological analyses to provide a clearer understanding of the taxonomic status, distribution and evolutionary origins of B. bodiensis.

Pollen studies reveal that B. bodiensis is a diplosporous apomict. Microsatellite genotyping of the holotype confirms it to be triploid, containing three subgenomes derived from Boechera cobrensis, B. fernaldiana and B. sparsiflora. Expanded microsatellite surveys detect this triploid genotype at 22 additional sites, primarily in Mono County, CA, USA. Morphological analyses of genetically verified specimens identify a consistent set of characters that distinguish B. bodiensis from co-occurring congeners.

The BMW enables high-resolution analyses of genome composition, reproductive mode and hybrid origins, making it a powerful tool for resolving taxonomic complexity in Boechera. Our case study of B. bodiensis highlights the effectiveness of combining molecular and morphological data to clarify species boundaries, inform conservation assessments and refine nomenclatural understanding in this notoriously difficult genus.