BAGGS, JOANNE E.* and JOYCE MASCHINSKI. The Arboretum at Flagstaff, 4001 S. Woody Mountain Rd., Flagstaff, AZ, 86001. - Detecting morphological and growth rate differences of a confusing Purshia complex using a common garden study.
Purshia subintegra (Kearney) Henrickson is a rare soil endemic
found in 4 populations across central Arizona. In the Verde Valley,
the range of P. subintegra overlaps with the more common
cliffrose, Purshia stansburiana (Torr.) Henrickson, and
introgression or hybridization occurs. Because P. subintegra
was federally listed as an endangered species in 1984, understanding
the dynamics of the hybrid complex is critical to the management of
P. subintegra as well as understanding the factors that limit
the distribution of P. subintegra. In a common garden study, we
examined the morphological and growth differences of P.
subintegra, P. stansburiana, and the introgressed form
across a soil gradient. The soil gradient consisted of soil from 3
habitats: undisturbed limestone outcrops where P. subintegra
grows, disturbed limestone roadsides where the introgressed forms
grow, and a wash where P. stansburiana grows. In a greenhouse,
we established plants from stem cuttings in 1 gallon pots using
amended soils from the 3 habitats and measured morphological
characteristics after 80 weeks. Using discriminant function analysis,
we could distinguish P. subintegra and P. stansburiana
but introgressed forms showed more phenotypic variability. Genetic
individuals of the introgressed forms also showed more variability
across the soil gradient than individuals of P. subintegra and
P. stansburiana. Using the same experiment, we measured
aboveground biomass after 84 weeks. Using analysis of variance, the
aboveground biomass was significantly different between species and
soil types. P. stansburiana grew the largest compared to P.
subintegra and the introgressed forms which had similar
aboveground biomass. Each species grew best in the soil from its
habitat. P. subintegra and the introgressed form grew best in
both undisturbed and disturbed limestone soils while P.
stansburiana grew best in soil from the wash.
Key words: common garden study, hybridization, limestone soil endemic, Purshia stansburiana, Purshia subintegra