Systematic and reproductive studies of Mimulus (Scrophulariaceae) in the Pacific Northwest : implications for conservation biology Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/44558h089

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  • 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.
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