| Summary: | The study of plants growing on unusual geologies has provided much insight
into evolutionary biology. Examination of models of speciation shows that edaphic
factors can serve as environmental triggers for models of speciation. The study presented
here investigated morphological, biochemical physiological, and ecological attributes of a
species that may have evolved under edaphic influence. Lasthenia califomica is a spring
annual endemic to California. Previous studies documented the existence of two races
(type-A and -C) based on flavonoid pigments, achene morphology, allozyme banding
patterns, and flowering time differences. These two races coexist in a population found
on a serpentine outcrop at Jasper Ridge Biological Preserve, California. Studies lasting
15 years have disclosed that the two races maintain a sharply-defined boundary on this
ridge. The ridge top is populated by type-C plants, and ridge bottom, by type-A plants.
Studies were conducted to determine if edaphic factors play a role in
maintaining this distribution pattern. Analyses of soil samples revealed significant
differences in the physical and chemical features of the soils harboring each race.
Analyses of plant tissue indicated that tissue concentrations of various elements in the two
races are significantly different. Multivariate tests indicated that certain soil (pH, Mg, Na)
as well as plant tissue (Na, Mg, Ca/Mg) characteristics are reliable in predicting each race.
Examination of soil and plant tissue samples from 22 populations agreed with several
patterns observed at Jasper Ridge. One of the most intriguing observations of the study
was that the concentrations of sodium found in type-A plants are over three times those in
type-C plants. Greenhouse studies revealed that the two races show differential responses in
germination, survival, growth, and phenology to ridge top and bottom soils, indicating
that edaphic factors are important in rrwintaining the distribution on this outcrop.
It is suggested that type-A plants are possibly more tolerant of edaphic
stresses than type-C plants. The role stress tolerance may have played in the evolution of
the species is discussed. It is implied that the two races of L. californica may qualify as
true edaphic races and that further studies are needed to determine if the races deserve
taxonomic recognition.
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