- Populations of an unknown species of Mimulus, herein
described as Mimulus hymenophyllus Meinke, were located
and studied near Horse Creek, a tributary of the Snake
River in eastern Wallowa County, Oregon. The new species
is differentiated from its apparent closest relative,
Mimulus jungermannioides Suksd., by an annual habit, long
petioles, corollas that are three to four times the length
of the calyx, rounded capsules, and seeds up to 0.85 mm
long. Mimulus hymenophyllus and M. iungermannioides are
members of the section Paradanthus, and are
morphologically allied with Mimulus moschatus Dougl. in
Lindl. and several related taxa. The Mimulus moschatus
complex of species is distinguished within the genus by
having firmly adherent placentae, glandular-sticky foliage
and stems, prismatic calyces with equal to sub-equal
teeth, elongate pedicels, and deciduous, funnelform
corollas ranging in color from canary to lemon yellow.
Mimulus hvmenophyllus is endemic to the steep canyons
of Horse and Cow Creeks in Wallowa County, at altitudes
ranging from 850 to 1300 m. The species is restricted to
the damp crevices of vertical basalt cliffs, often growing
in the shade under overhangs. The surrounding plant
community is dominated by several coniferous species,
primarily Pseudotsuga menziesii, pinus ponderosa, and
Abies arandis. The habitat of M. hymenophyllus is
isolated, and is presently not in danger from human
disturbance. However, the species is currently maintained
as a state and federal candidate for listing as threatened
or endangered, based on limited abundance and narrow
Studies of the seed and seedling biology of Mimulus
hymenophyllus and its Pacific Northwest relatives (i.e.,
M. moschatus, M. floribundus, M. jungermannioides, M.
patulus, M. pulsiferae, M. washingtonensis, and M.
breviflorus) were also conducted. Germination trials
indicated that seeds of M. moschatus, M. jungermannioides,
and M. floribundus are capable of germination immediately
or soon after capsules dehisce, and do not become dormant
upon later exposure to warm or cold temperatures. Seed
lots of M. hymenophyllus and M. breviflorus germinate
rapidly when first mature, but subsequently develop
complete or partial dormancy after prolonged exposure to
late summer temperatures. Dormant seeds of these species,
as well as those of M. patulus, M. Dulsiferae, and M.
washingtonensis which are dormant when capsules dehisce,
will germinate readily after several weeks of cold-wet
Four of the five species lacking innate seed dormancy
develop inflated fruiting calyces that temporarily trap
seeds as capsules dehisce. This prolongs the dispersal
rate of seed crops, thereby minimizing the potential for
catastrophic seedling mortality due to mass germination of
cohorts during unfavorable environmental conditions.
These species retain seed on the parent plant for
significantly longer periods than species with unmodified
calyces. Seed dispersal from parent plants is
accomplished by wind and flowing water, except in M.
hvmenophvllus, where negatively phototropic pedicels
orient ripe capsules towards the darkened cliff substrate
for dispersal directly into crevices.
Two of the rarest species studied, M. hymenophyllus
and M. patulus, were found to co-occur in nature with an
indigenous and rather weedy, unrelated species of Mimulus,
i.e., M. nasutus Greene. Experimental plantings showed
that seedling lots of M. nasutus emerge sooner and over a
shorter period than those of the two uncommon species,
suggesting that M. nasutus may outcompete them and thereby
contribute to their rarity.
Seedlings of M. breviflorus and M. floribundus, which
typically occur in habitats subject to sudden fluctuations
in soil moisture, exhibit adaptations for accelerated
sexual reproduction under experimental drought conditions.
This trait, when coupled with inflated fruiting calyces,
enables these species to exploit unpredictably arid
environments despite the potential disadvantage of
nondormant seeds. Mimulus jungermannioides and M.
moschatus are not adapted for precocious sexual
maturation, and offset their lack of seed dormancy by
having a perennial life cycle and by occurring in more
predictably mesic habitats. Significant differences
between the annual and perennial species were observed in
the timing and amount of seed production during droughtstress.
The information provided in this thesis will be
valuable to systematists and conservation biologists.
Several of the species studied have been promoted for
protection under endangered species laws. The formal
naming of Mimulus hymenophyllus legitimizes efforts for
the management of this unique species, while seed and
seedling biology data will be important to germplasm
studies, phylogenetic assessments, and possible reintroduction
of species or populations should extirpation