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Oregon, of which two are old historical records that are probably no longer extant. Most of <br /> the known populations in Oregon (19 EOR's) are within the west Eugene area. <br /> Habitat Description: Throughout its range, Aster curtus is a species of native prairie <br /> remnants. In Oregon, populations are found in both wet prairie and upland prairie <br /> communities, as well as in open situations in oak savannas. At Rickreal Ridge in Polk Co., <br /> the species grows on an open rocky ridgetop. Prior to alteration of native prairies by <br /> settlers, A. curtus may have been a widespread, if not common, species of native prairie <br /> habitats in the Willamette Valley. However, most extant sites in west Eugene are in wet <br /> prairies. Soils of the wet prairie sites are mapped as the Dayton and Natroy series. Soils of <br /> upland prairie sites are mapped as Nekia, Pengra, Philomath, Stayton, and Witzel series. <br /> Growth habit: Strongly clonal, rhizomatous perennial herb, 1 -3 dm. tall, usually simple and <br /> unbranched up to a close terminal cluster of heads, glabrous except for scabrous- ciliolate <br /> margins of leaves. This species can form large colonies with numerous shoots (ramets), but <br /> the numbers of genets in such populations is probably to be much less than the number of <br /> ramets, often by several orders of magnitude. <br /> Leaves: 2.5 -3.5 cm. long, 5 -9 mm. wide, oblanceolate, tapering to the essentially sessile <br /> base. <br /> Flowers: Rays 1 -3, typically 2, 1 -3 mm. long, whitish, shorter than pappus; disk flowers <br /> few, mostly 9 -21, pale yellowish with purple anthers <br /> Fruit: Achenes with pappus. In Washington populations, only about 20% of seeds contained <br /> endosperm and thus were considered to be "filled" seeds ( Clampitt 1987). <br /> Seed germination rate, seed bank persistence: Clampitt (1987) found that a high <br /> percentage of filled seeds germinated, under a variety of treatments. The seeds apparently <br /> require light to germinate. The highest average germination rate (96 %) and most rapid <br /> germination occurred with seeds that had been stratified for 45 days at 5 degrees C. <br /> Unstratified seeds germinated at an average rate of 66 %, and took considerably longer to <br /> germinate. <br /> Phenology: Shoots appear in mid spring, and are evident for field surveys beginning at least <br /> in May, but flowering is in mid to late summer, mostly July and August in the southern <br /> Willamette Valley. Fruits mature and disperse in August and September. <br /> Reproductive biology and breeding system: Reproduces both clonally (by spreading <br /> rhizomes) and by seed. Insect visitors are necessary to effect pollination. Flower heads are <br /> protandrous (stigmas expand through the connate anthers several days after anthesis), an <br /> adaptation typical of obligate outcrossing species ( Clampitt 1987). However, hand <br /> pollination experiments to determine whether or not the species is self - compatible have not <br /> been done. <br /> 4 <br />