December 2012 Number 1 - Utah Native Plant Society

Utah Native Plant Society
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Family 7
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Family 11
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PRINCIPAL COMPONENT 2
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PCA 2
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One Individual
Two Individuals
Three Individuals
Four Individuals
Five Individuals
PRINCIPAL COMPONENT 1
Figure 4. Scores on the first two axes from Principal Components Analysis of AFLP (amplified fragment length
polymorphism) data for greenhouse-grown individuals belonging to 15 half-sib familes collected from the P. argillacea
Tucker population in 2004. Point size reflects number of individuals with identical AFLP genotypes.
argillacea indicated that individuals tended to group
together by year much more than by population. These
data suggest a persistent seed bank, which means a fraction
of the seeds not only remain in the soil, but are viable
for at least one year after production (Thompson
and Grime 1979). A site characterization study of P.
argillacea supported this hypothesis by suggesting that
the seed bank reservoir contains an accumulation of
seeds from many different years (Armstrong 1992).
Preliminary results from a long term seed retrieval study
with P. argillacea also support the existence of a longlived
seed bank in this species. Few or no seeds have
germinated in the field during the first two years, and
most are still in a state of primary dormancy (Meyer
unpublished data). This type of seed bank structure has
also been reported in Phacelia secunda. Seeds from P.
secunda were collected and allowed to germinate, and
after three years a considerable fraction of the seeds remained
viable but ungerminated (Cavieres 2001).
PCA also suggests that collections from a single year
and population of P. argillacea would depict a very narrow
genetic diversity within the organism. A persistent
seed bank can function as a genetic memory by accumulating
seed genotypes from different years (Cabin et al.
1998). In the case of the rare annual Clarkia springvillensis,
analysis of seed bank samples illustrated significantly
higher within-seed bank genetic diversity when
compared to the adult population (McCue and Holtsford
1998). The same could be true for P. argillacea, as evidenced
by the pattern seen in the PCA (Figure 3). The
seed bank must have a higher genetic diversity than the
established plants in any one year, because of the wide
range of diversity seen when comparing years. A similar
situation was found in Phacelia dubia, which has small
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