This week, the molecular ecology lab took a field trip to Marin County to visit more wild populations of our focal plant species, Mimulus guttatus(=Erythranthe guttata).


On Tuesday, September 24, 2019 at 1:00PM, the class left in two passenger vans, and headed to Red Rock Spring, Marin County.  The site is located at a gravel pull-out on the east side of Highway 1, just South of Stinson Beach.


After getting lost on a Google-maps detour, we found the gravel parking lot and joined the rest of the class. We observed a natural spring, flowing out of PVC pipes from the hillside, and the population of Mimulus guttatus growing in the spring-fed puddle.  The population had many more flowers on display than we had seen at the populations from the Lab 3 field trip, two weeks prior.  All of the flowers appeared to have closed stigmas, suggesting that they had been pollinated.  The habitat was a steep, disturbed hillside that had been carved away to make room for Highway 1.  The population, although fed, seemingly perennially, by the stream, was in full sun, and we can vouch for the heat stress.


After leaving this population, the vans left and headed south along Highway 1, eventually turning east and arriving at the Redwood Creek Trailhead.  The trail crosses Redwood Creek, a perennial creek that flows through Muir Woods, all the way to Muir Beach.  The class followed the trail until we got to an old wooden bridge that crosses the creek.  We veered to the right, down the horse bypass trail.  Once we got to the creek, we followed it upstream, searching for Mimulus guttatus.  The creek is surrounded by a dense riparian corridor, a continuous canopy, and characterized by a gravelly, sandy substrate in the creek bed.


By now, the class recognized the familiar habitat, and expected to see our monkey flower growing near the waters’ edge.  After ducking under vegetation, crossing log bridges, and only a few submerged shoes, I spotted a population of Mimulus on a dry gravel bar along the edge of the creek.  The individuals were numerous, small, vegetative rosettes.  About 100 ft further upstream, the class found another populations of small Mimulus rosettes.  These populations had not yet flowered.  We considered the likelihood of these plants flowering before winter storms drown them out or wash them away.  We also pondered the movements of pollinators, and how that might affect gene flow between the populations we’ve seen in the field.


Eventually we made our way back along the creek, and headed back to campus.


Note: Sorry about the absence of photos, my phone was dead before arriving at the first population.