Occurrence and phylogeny of the endangered Texas endemic Echinocereus fitchii subsp. albertii

Summary: Echinocereus fitchii subsp. albertii (L.D.Benson) W.Blum & Mich.Lange, also known as Echinocereus reichenbachii var. albertii L.D.Benson, is a south Texas, USA endemic. The plant, commonly called black lace cactus, is listed as a federally endangered species in the United States. The objectives of this study are to 1 – survey populations of black lace cactus to determine current occurrence status, 2 – examine habitat and morphological features of black lace cactus across occurrences and 3 – examine the phylogeny of the E. reichenbachii-fitchii species complex to decipher the closest evolutionary relatives of black lace cactus. We photo-documented E. fitchii subsp. albertii individuals and confirmed extant populations in Kleberg, McMullen, and Refugio counties, Texas. Our study identified additional populations extending the sub-species' distributional range into Atascosa and La Salle counties, Texas. Flower colour of E. fitchii subsp. albertii is characteristic of the E. fitchii group. Central spines are absent to rare in E. fitchii subsp. albertii individuals in most populations, with only plants growing in the Kleberg Co. population commonly exhibiting central spines. We used genome skimming and assembly of nuclear ribosomal regions and nearly complete chloroplast genomes to examine phylogenetic relationships of fifteen taxa of Echinocereus. The most significant finding emerging from this phylogenetic study is that two distinct chloroplast genome lineages can be distinguished in E. fitchii subsp. albertii. One lineage includes individuals from Refugio Co. and McMullen Co. populations which are most closely related to E. reichenbachii subsp. caespitosus. The other lineage includes individuals from Atascosa and Kleberg Cos., which are most closely related to E. fitchii subsp. fitchii. These two lineages are not defined by geographic proximity.