Astragalus pycnostachyus species complex

Astragalus pycnostachyus A. Gray (Fabaceae) is a short-lived perennial herb found primarily in marsh habitats along the California coast. It is split into two described varieties: coastal milkvetch (var. pycnostachyus) is listed as rare and found in San Mateo, Marin, and Humboldt Counties of northern California, and the endangered Ventura marsh milkvetch (var. lanosissimus Rydb. (Munz & McBurney)) is now found only in a few highly managed sites in Ventura County and Santa Barbara Counties. Here, we use genomic data (ddRADseq) to 1.) assess phylogenetics of the A. pycnostachyus species complex, and whether taxonomy reflects monophyletic groupings, 2.) quantify genetic difference within and between A. pycnostachyus var. pycnostachyus and var. lanosissimus. And finally, 3.) determine genetic diversity of the nine maternal lines employed in var. lanosissimus conservation at North Campus Open Space (NCOS) in Goleta, California, one of two localities where it is managed. Our phylogenetic and genetic structure analyses reveal that Astragalus pycnostachyus is composed of two main genetic groupings, which correspond to the currently recognized varieties. Furthermore, the northern variety is split into two genetic groups which correspond to geographic location, one group of Bay Area samples and the other of Humboldt County samples. Pair-wise genetic differentiation between the southern California variety, and the northern Californian genetic groups show that there are significant barriers to gene flow between them (FST=0.59-0.76). In addition, our results show that despite the limited number of maternal lines of var. lanosissimus plants utilized in restoration out plantings at NCOS, they harbor moderate amount of genetic diversity (Pi =0.061) but will require strategic management to protect that existing diversity. We also recommend that the southern variety and the two northern Californian genetic groups are managed as separate genetic entities, but that within these groups, effort is made to support factors that facilitate gene flow and a healthy population size. This study of the phylogeography, population structure, and genetic health of Astragalus pycnostachyus is the first using next gen sequencing technology and data to provide information for future management plans for this species.