Oral Paper

         Systematics

A new hypothesis for the origin and species relationships of the scaly-bracted green leaf manzanitas (Arctostaphylos)

Presenting Author
Tito Abbo
Description
Arctostaphylos (manzanitas), the most diverse woody genus within the California Floristic Province, is regarded as a taxonomically and evolutionarily complex system. High diversity and hybridization pose challenges for both species delimitation and morphological identification. A key debate in developing a classification system for manzanitas that accurately reflects evolutionary relationships is whether taxa that share morphological traits derived those traits from descent or homoplasy. The taxa that I am calling the SBGL (scaly-bracted green leaf) manzanitas all share the combined traits of scale-like inflorescence bracts and shiny green leaves. In manzanitas, bracts can be leaf-like, scale-like, or fleshy, and leaves can be green, gray-green, or glaucous. Munz and Roof considered many low-growing SBGL manzanitas to be aligned with A. uva-ursi and erect SBGL manzanitas to be aligned with A. pungens. Wells, on the other hand, considered Central Coast SBGL manzanitas as subspecies of A. hookeri. Markos et al. (1998) using nuclear ITS and 26S loci found limited but sufficient phylogenetic resolution to conclude that A. hookeri was paraphyletic without direct evidence of alignment with A. uva-ursi nor A. pungens. This suggested that the SBGL phenotype was derived multiple times independently. However, using reduced representation genomic sequencing (ddRADseq), I present evidence that SBGL manzanitas are not independent but rather are associated due to hybridization. The hybrid origin of SBGL manzanitas appears to be associated with one or more hybridization events involving two very distantly related manzanita lineages (the two ITS clades), which were thought to have sufficiently diverged to develop reproductive isolation. Herein, I present the hypothesis that the Central Coast is a large hybrid zone which has led to the origin of several narrow endemic SBGL manzanita lineages. Further, I present evidence for numerous hybrid origins of the taxa morphologically identified as A. benitoensis and A. parryana ssp. parryana.