The Mimulus washingtonensis complex is a group of morphologically similar
species centered in the Pacific Northwest. All are rare, and most are under
consideration for listing as endangered. Morphometric and pollination data were
used in developing a revised taxonomy for the group. Five species and two varieties
are recognized. Mimulus pulsiferae Gray is the most widespread, occurring from
southern Washington to northern California. Mimulus hymenophyllus Meinke and
M. jungermannioides Suksd. are cliff species endemic to river drainages in northern
Oregon. Mimulus washingtonensis Gand. occurs in east-central Oregon and western
Idaho, represented by the var. washingtonensis and var. ampliatus (Grant) Meinke
comb. et stat. nov., respectively. Mimulus patulus Pennell is resurrected from
synonymy and differentiated from M. washingtonensis on the basis of morphology,
distribution, and pollination biology. This autogamous species includes var. patulus,
occurring in the Snake River drainage, and var. montanus Meinke var. nov.,
primarily from the northern Rocky Mountains.
Mimulus evanescens Meinke sp. nov. is described from an extant population
in Lassen County, California, and historic collections from widely scattered stations
in Oregon and Idaho. The new species is morphologically intermediate between M.
breviflorus Piper and M. latidens (Gray) Greene. Calyx and leaf morphology also
suggest an affinity to M. grayi Grant, M. inconspicuus Gray, and M. acutidens
Greene, of cismontane California. Mimulus evanescens should be considered
critically endangered, because of its limited numbers and habitat degradation.
Mimulus washingtonensis is pollinated by small native bees, primarily two
species of Dialictus (Halictidae). These bees were specific to Mimulus flowers but
did not distinguish between flowers of M. washingtonensis and M. guttatus DC., a
related species that increases with habitat disturbance. Experiments showed that
mixed pollen loads diminish seed set in M. washingtonensis, since the thigmotropic
stigma of that species closes permanently after any amount of conspecific pollen is
applied. Although M. washingtonensis has a low pollen/ovule ratio (29.9), it is
considered facultatively xenogamous based on floral morphology, stigma sensitivity,
and autogamous seed set levels. Populations occurred in small, edaphically
restricted patches, and they exhibited seed set reductions related to outcrossing
distance. Substrate disturbance may limit reproduction in M. washingtonensis by
changing population structure, threatening pollinators, and increasing competition for
pollination by promoting growth and flowering of M. guttatus. / Graduation date: 1992
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/36809 |
| Date | 08 May 1992 |
| Creators | Meinke, Robert James |
| Contributors | Chambers, Kenton L. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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