December 2012 Number 1 - Utah Native Plant Society

Calochortiana December 2012 Number 1
Molecular Genetic Diversity and Differentiation in Clay Phacelia
(Phacelia argillacea Atwood: Hydrophyllaceae)
Steven Harrison
Brigham Young University, Provo, UT
Susan E. Meyer,
US Forest Service Rocky Mountain Research Station, Shrub Sciences Laboratory, Provo UT
and Mikel Stevens,
Brigham Young University, Provo, UT
Abstract. Clay phacelia (Phacelia argillacea Atwood) was listed as federally endangered in 1978. It is known from
only two populations in Spanish Fork Canyon, Utah. Samples were taken in each of three years from each of these
two populations. We used AFLP markers to assess the genetic relatedness between the two populations and degree of
differentiation between P. argillacea and three of its congeners. Six AFLP primer combinations resulted in 535 reliable
marker loci of which 124 were polymorphic. Phacelia argillacea is genetically distinct from both its close and
distant congeners. The two P. argillacea populations were not strongly differentiated, suggesting that gene flow between
these populations probably occurred historically. In contrast, cohorts establishing in different years within a
population were often genetically differentiated. Sampling in a single year would seriously underestimate genetic
diversity in this species.
Phacelia argillacea Atwood (clay phacelia) is a narrow
endemic presently known from two locations approximately
8 kilometers apart in the Spanish Fork Canyon,
Utah County, Utah (Figure 1). The genus Phacelia
is the largest in the Hydrophyllaceae. Phacelia argillacea
is a member of the Crenulatae group of section Phacelia,
subgenus Phacelia and is thought to be most
closely allied to P. glandulosa Nutt., a species of wide
distribution in extreme eastern Utah, western Colorado,
Wyoming, eastern Idaho, and Montana (Atwood 1975).
Another apparently closely allied species is the recently
described P. argylensis Atwood (Welsh et al. 2003),
known only from the type location in Argyle Canyon,
Carbon County, Utah (Figure 1). The Crenulatae group
(which consists of approximately 35 species) differs
from other species of Phacelia in producing four-seeded
capsules, faveolate seeds with a central ridge on the
ventral side, and have a chromosome number of n=11
(Atwood 1975).
Recent taxonomic work in the genus Phacelia has
confirmed the placement of P. glandulosa within the
Crenulatae but has not included either P. argillacea or
P. argylensis (Garrison 2007, Gilbert et al. 2005). Our
goal was to examine molecular genetic diversity within
and among the two known populations of P. argillacea
as a necessary step in designing strategies for introducing
new populations of this species on public land. We
also wanted to make a preliminary assessment of the
degree of differentiation between P. argillacea and its
close congeners P. glandulosa and P. argylensis. We
included the more distant congener P. crenulata Torr.
ex S. Wats. as an out group in the analysis.
Phacelia argillacea is an annual or biennial and has
years when few or no actively growing plants are present.
Its seeds germinate from spring to late summer or
early fall and produce a rosette of leaves which grows
during the winter months and bolts in the spring to produce
a flowering shoot (Armstrong 1992, Meyer personal
observation). The species is an edaphic endemic
that is confined to steep hillsides of the Green River
shale formation. Because of its restricted habitat and
small and widely fluctuating population size, P. argillacea
was declared an endangered species in 1978 (US
Fish and Wildlife Service 1978, 1989).
In 1990, The Nature Conservancy purchased the
Tucker site, which at the time was the only known extant
population for P. argillacea, and fenced it to prevent
damage from grazing and trampling by deer and
sheep and from disturbance caused by highway and railroad
construction (Armstrong 1992). The plant was
later rediscovered at the Railroad site, further down the
canyon (Figure 1, inset). This population is on private
land and is not fenced or managed for conservation.
Known impacts to the Railroad site are highway widening
coupled with the construction of a retaining wall,
subsequent erosion, and trailing and grazing of domestic
and native ungulates. P. argillacea may also be threatened
by invasive weeds and drought.
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