New Western North American Taxa of Arceuthobium (Viscaceae) Frank G. tHaiksworth USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins, Colorado 80526, U.S.A. Delbert Wifens Department of Biology, University of Utah, Salt Lake City, Utah 85112, U.S.A. Daniel L.Department of Plant Biology, Southern IllinoisABSTRACT. Several new names are proposed for ataxonomic revision of the dwarf mistletoes (.-rceu-thobium). Two new species from northwestern Cal-ifornia and southwestern Oregon are described: 1.siskitouense, a parasite of knobcone pine, and A.monticola, a parasite of western white pine. Alsodescribed as new is A. littorum, a parasite of Mon-terey and bishop pines in coastal California. Arcru-thohiurm tsuigens is segregated into two subspecies:subspecies tsugcnse, primarily parasitic on westernhemlock, and subspecies nmertensi(anae, primarilyparasitic on mountain hemlock. In preparing a revision of our monograph ondwarf mistletoes (.Arceuthobium, Viscaceae) (Ilawk-sworth & Wiens, 1972) and for our treatment ofthe Viscaceae for the new Jepson :Iltnuial of theFlowering Plants of Ca!li/ornia, we have continuedto investigate the systematics of this economicallyimportant genus of conifer parasites (Hawksworth& Wiens, 1976, 1977, 1980, 1984. 1989; Nick-rent, 1986, 1987; Nickrent & Butler, 1989, 1990,1991; Nickrent & Stell, 1990; Nickrent et al.,1984). Here we describe three new species thatparasitize pines in Oregon and California, and wealso segregate the hemlock dwarf mistletoe into twosubspecies. Two of the new species are endemic tothe Siskiyou-Klamath Mountains floristic provinceof northwestern California and southwestern Ore-gon, an area well known for its high degree of plantendemism (Smith & Sawyer. 1988). Only brief descriptions of the new taxa, theirrelationships to closely related taxa, and selectedcollections representing the host and geographic dis-tribution of the new taxa are cited here. Additionaldescriptions, illustrations, complete specimen cita-tions, and distribution maps will be presented in ourrevised monograph of the genus, which is nearingcolmpletion. The methods used for our morphologicalNoVON 2: 204 211. 1992.NickrentUniversity, Carbondale, Illinois 62901, U.S.Aanalyses are as described by Hawksworth & Wiens(1972).Arceuthobium siskiyouense Hawksworth, Wiens & Nickrent, sp. nov. TYPE: U.S.A. Oregon: Josephine County, Oregon Mountain Road, 6 mi. SW of O'Brien, parasitic on Pinus attcen-uata, T. 41 S., R. 9., , Sect. 9, 42001'N, 123�46'W, elevation 650 m. 20 July 1987, 1). fie'ns )6756 (holotype, UIS; isotypes, FPF, MO, ORE, OSC, 1C). Plantae 6-10 (8) cm altae; surculi brunnei, parce fla-bellate ramosi; surculi principales basi 2 2.5 mm dian.,internodiis tertiis 6 15 (9) mm longis, 2 niii latis; floresstarninati 3-4-meri; fructus maturi 4 inni longi, 2.5 mmlati; anthesis mense Septembri; fructus maturitas menseSeptembri-Octobri. In Pino attenuata parasiticae. Plants 6-10 (mean 8) cm tall, brownish, flabel-lately branched, predominant shoots 2 2.5 mm diam.at base, third internode from base 6 15 (mean 9)mm long and 2 mm wide; staminate flowers 3-or4-partite; mature fruit 4 mm long and 2.5 mm wide;anthesis in September; fruits mature in Septemberand October; parasitic principally on Pinus atten-Hata. We previously included this dwarf mistletoe underA. campylopoduin (Hawksworth & Wiens, 1972,1984), but noted an anomalous situation near Gas-quet, Del Norte County, California. where a dwarfmistletoe (then presumed to be A. campylood)oum)was conmnon on Pinus attenuatl but rare on as-sociated P. ponderosa (Iawksworth & Wiens,1972). This situation is now readily explained, be-cause the taxon on P. attenuata is .A. sis kii ourtnsenot A. canpyVlopodum. -Arceuthobiurn siskivouense is a local endemicrestricted to the Siskivou-Klamath Mountains ofsouthwestern Oregon (Curry and Josephine counties)
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