. The Canadian field-naturalist. Natural history; Sciences naturelles. 176 The Canadian Field-Naturalist Vol. 120 shadow effect prevails in this area due to the pres- ence of the Coast-Cascade Mountains to the west. Within this region, CoUomia tenella occurs on an eroded, steeply-sloped, southeast-facing section of a sandy ridge (Figure 3). The sandy ridge, formed by flu- vial processes during recent glaciation, consists of fine- textured sands. The eroded sections of the slopes are sparsely vegetated with about 20% cover. The vegeta- tion consists of a variety of herbs and shrubs including Ar
. The Canadian field-naturalist. Natural history; Sciences naturelles. 176 The Canadian Field-Naturalist Vol. 120 shadow effect prevails in this area due to the pres- ence of the Coast-Cascade Mountains to the west. Within this region, CoUomia tenella occurs on an eroded, steeply-sloped, southeast-facing section of a sandy ridge (Figure 3). The sandy ridge, formed by flu- vial processes during recent glaciation, consists of fine- textured sands. The eroded sections of the slopes are sparsely vegetated with about 20% cover. The vegeta- tion consists of a variety of herbs and shrubs including Arrow-leaved Balsamroot {Balsamorhiza sagittata). Timber Milk-vetch {Astragalus miser). Narrow-leaved CoUomia (CoUomia linearis). Thread-leaved Phacelia {Phacelia linearis). Silky Lupine {Lupinus sericeus). Saskatoon (Arnelanchier alnifolia), Dalmation Toad- flax (Linaria genistifolia ssp. dalmatica), Cheatgrass (Bromus lectorum), and Bluebunch Wheatgrass (Pseu- doroegneria spicata). Scattered Douglas-fir (Pseudot- suga menziesii) and Ponderosa Pine (Pinus ponderosa) also occur on the ridge (Figure 3). Biology There is no information available on the biology and ecology of CoUomia tenella in the literature. Since it is an annual plant it appears to be absent in some years if environmental conditions for seed germination and/ or seedling survival are not favourable. Other annual members of the genus are self-compatible and self- pollinating (Wilken 1993). Seeds may be dispersed by animals since they are sticky when moistened. Population Attributes The single population of CoUomia tenella, covering an area of less than 60 m-, was discovered in 1997 in the Similkameen River valley, west of Princeton, British Columbia (Figure 2; Douglas et al. 1998a). Counts for the population in 1997, 2000, 2002, 2003 and 2004 were 10, 1,0, 127 and 0, respectively. In 2003, the area occupied was ca. 56 square metres, with plants in four groups of 56, 67, 1 and 3 plants. These fluctuations indicate t
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