Comments: Grows in damp to wet soils, a habitat preference which it has in common with other Rorippa species (Stuckey 1972). Populations have been observed near all types of bodies of water, including the Columbia River, intermittent snow-fed streams, permanent lakes, snow-fed lakes, internally-drained lakes which may be dry for extended periods of time, wet meadows, irrigation ditches and roadside ditches. A common feature of known sites is inundation for at least part of the year. Individuals are usually found in open, high light habitats, with low vegetative cover. The species grows on a wide variety of soil types including clay, sand, gravel, sandy silt, cobblestones and rocks. 1200-1800 m. Descriptions of habitat at a selection of specific locations follow.
Populations along the Columbia River are currently located on stretches of river that are relatively free-flowing, although flows are impacted on a hourly, daily and seasonal basis by upstream dam operations (Scherer 1991; Pam Camp, personal communication; Lynn Cornelius, personal communication; Gehring, personal observation). Population sites on the lower Columbia below Bonneville Dam experience unpredictable inundation by the river due to (1) dam operations, (2) tides and (3) water flow from the Willamette River at Portland (Scherer 1991; Gehring, personal observation). In most years, they are above water for only two to three months during the growing season (Scherer 1991). At Pierce Island, most of the populations are on cobblestone beaches and banks, although the beach on the north side of the island has a layer of sandy silt on top of the cobblestones. Many of the plants are found in a linear zone of two to three meters, parallel to the river. One population on Pierce Island is growing in sandy silt in a slough that contains water only when the river is relatively high (Cornelius, personal communication; Gehring, personal observation). This population has high vegetative cover (Gehring 1990); the most frequent associated species in 1991 included Deschampsia caespitosa and Equisetum spp. (Gehring, personal observation). Plant species found growing frequently with Rorippa columbiae on the cobblestone banks and beaches of Pierce Island in 1984 included Artemisia lindleyana, Rorippa curvisiliqua, Aster subspicatus, Polygonum persicaria, and Salix fluviatilis (Cornelius 1985). The cover and frequency of Artemisia lindleyana and Helenium autumnale have increased dramatically on the cobblestone beaches since 1984 (Lynn Cornelius, personal communication). Plants at the mouth of Hamilton Creek on Pierce National Wildlife Refuge are located on the rocky north bank of the river. Associated species include Coreopsis atkinsonia, Helenium autumnale, Artemisia lindleyana, Mentha arvensis, and Salix fluviatilis (Harris 1992). Populations have also been observed in open, bare gravelly habitat with little vegetation on Ives Island (Washington Natural Heritage Information System) and on Hamilton Island (Lois Kemp, personal communication). On the river bar at the old mouth of the Sandy River, Rorippa columbiae occurs with Arabidopsis thaliana, Draba arabis, Cerastium nutans, Cerastium viscosum, Scleranthus annuus, Veronica arvensis, Chenopodium botrys, Poa annua, Aira caryophylla, and Marsilea vestita (Oregon Natural Heritage Program Data Base).
There are also numerous populations on the Hanford Reach of the Columbia River. The visual habitat features of populations on the Hanford Reach appear to be similar to those of the populations downstream of Bonneville Dam. Plants only grow below the high water level of the river where vegetative cover is sparse (Sauer and Leder 1985). They are inundated frequently during the growing season (Camp, personal communication; Gehring, personal observation). On the Hanford Reach, Rorippa columbiae grows on wet silty soil beneath a layer of gravel (Sauer and Leder 1985; Camp 1992; Gehring, personal observation), sand with cobbles (Baird 1984; Schuller 1984; Camp 1992), and sandy silt without rocks (Camp 1992; Gehring, personal observation). Associated species include Artemisia lindleyana, Machaeranthera canescens, Salix exiqua, Salix spp., Coreopsis atkinsoniana, Agrostis spp., Helenium autumnale, Plantago major, Melilotis alba, Rorippa spp. (Schuller 1984), Lindernia anagallidea, Veronica spp. (Baird 1984), Apocynum spp. (Camp 1992), Morus alba (Camp 1992; Gehring, personal observation), Phalaris arundinacea, Verbena bractata, Veronica anagalis-aquatica, and Cyperus aristatus (Sackschewsky, personal communication, 1992a).
In south-central Oregon, populations are known from Malheur Lake (Harney County), an internally-drained basin. Water levels at Malheur Lake began increasing in 1982, peaked in 1987 to a height not recorded since settlement by Europeans, and have been rapidly receding since 1987. The lake is expected to be dry in 1992 (Nora Taylor, personal communication). Associated species include Sarcobatus vermiculatus, Artemisia tridentata, Hordeum jubatum, Heliotropium curassavicum, and Potentilla anserina (Kaye and Massey 1991). Populations on the eastern/southeastern shore of Malheur Lake are or were located near the 4100 foot contour line, which was the high water level of the lake in the 1980's (Kaye and Massey 1991). The soil at these sites is now dry (Nora Taylor, personal communication). A number of small populations were found in 1988 after Malheur Lake began receding (Oregon Natural Heritage Program Data Base; Nora Taylor, personal communication); these populations were unknown before lake levels increased in the early 1980's (Nora Taylor, personal communication). Kaye and Massey (1991) were able to relocate only a third of these populations in 1990. The remaining populations were in microsites that retained moisture (Kaye and Massey 1991); for example, plants were found at the bases of large Artemisia tridentata and Sarcobatus shrubs, along the edges of flood debris such as pieces of barn siding, and in open but low-lying sites with standing water, including on an infrequently used road (Kaye and Massey 1991). The plants on the northeastern shore of Malheur Lake are also near the 4100 feet contour line (Kaye and Massey 1991; Oregon Natural Heritage Program Data Base, 1992). The plants are growing on ridges parallel to the lake shoreline; the ridges have clay on the surface (Nora Taylor, personal communication).
In Lake County, Oregon, populations are known from Featherbed and Foley Lakes, which are flat, shallow basins (Kaye and Massey 1991). Featherbed Lake normally contains water year-round, but was dry in 1978, 1990 and 1991 (Kaye and Massey 1991; Ginger King, personal communication). Foley Lake is fed by an intermittent stream from Featherbed Lake and usually has water only in the spring (Ginger King, personal communication). At both lakes, the plants are growing in silty clay and sandy soils and the populations are located in open, high light sites (Ginger King, personal communication). Associated species at Featherbed Lake include Monolepsis nuttalliana (20-25% cover), Artemisia arbuscula (20%), Arnica chamissonis (20%), Camissonia tanacetifolia (4-5%), Sitanion hystrix (trace), Bromus tectorum (trace), and Juncus sp. (trace). The Arnica and Sitanion were largely confined to the upper, drier, more rocky portions of the monitoring plots, and the Camissonia and Monolepsis were restricted to the lower, more moist portions of the plots (Kaye and Massey 1991. At Foley Lake, associated species include Camissonia tanacetifolia and Phacelia thermalis (Kaye and Massey 1991). Plants are also known from Binkey Lake (Kaye and Massey 1991). In 1983, associated species there included Camissonia tanacetifolia, Downingia spp., Iva axillaris, and Muhlenbergia richardsonis. Plants are also known from Silver Lake, from a Scirpus acutus marsh. In 1985, associated species at Silver Lake included Potentilla newberryi, Camissonia tanacetifolia, Epilobium paniculatum, Hordeum jubatum, and Rumex crispus. There were also small populations in a roadside ditch near Paulina Marsh in 1985 (Oregon Natural Heritage Program Data Base). They were observed growing in a wet meadow community with Hordeum jubatum, Camissonia tanacetifolia, Potentilla newberryi, Carex athrostachya, and Ranunculus cymbalaria.
In Klamath County, Oregon, plants occur in an intermittent stream bed on the northeast flank of Stuckel Mountain. The stream flows through a ponderosa pine, juniper and sagebrush community at approximately 5000 feet (Oregon Natural Heritage Program Data Base). The stream is fed by snowmelt and flows in the spring, but if there is little snowpack (as in 1991 and 1992), then it may not flow at all or only for a short period of time (Lou Whiteaker, personal communication). The substrate is sand and gravel on a slope of 1 to 2% (Oregon Natural Heritage Program Data Base).
In California, Siskiyou County populations occur at two lakes in the Shasta-Trinity National Forest: White Deer Lake and Dry Lake. White Deer Lake is a small meadow depression at 4590 feet in elevation that floods in wet years (California Natural Diversity Data Base). The lake has been dry for several years and lodgepole pine is invading the lake bed (Julie Nelson, personal communication). The population occurs in sandy soil in a small artificial pond constructed as a stock pond (California Natural Diversity Data Base; Julie Nelson, personal communication). The plants grow in clusters in an open, high light environment. Rorippa columbiae is found growing near Eryngium aristulatum, Juncus balticus (California Natural Diversity Data Base) and Oenothera tanacetifolia (Julie Nelson, personal communication). Dry Lake, where plants occur on the eastern margin,.is sandy with a hard soil pan near the surface. Normally, it is flooded for three to four months with the water level sometimes above three feet. Associated species include Pinus contorta, Arnica spp., Camissonia spp., Lupinus selinus, Penstemon shastensis, and Juncus balticus (Julie Nelson, personal communication).
Populations are also known from the shores of Clear Lake Reservoir in the Klamath Basin National Wildlife Refuge (Modoc County, California). Clear Lake is at 4480 feet in elevation and water levels decline seasonally (California Natural Diversity Data Base). In 1992, stems of Rorippa columbiae were scattered around the margins of the lake and up Willow Creek, which drains into Clear Lake (Mary Paezel, personal communication). The plants are growing in wet areas near the water's edge, on pumice sand, on higher mud flats of the old lake shore (due to drought, the water levels in the lake have decreased over the last several years) (Mary Paezel, personal communication), and among volcanic boulders in the inundation zone (California Natural Diversity Data Base). In general, plants are found away from competing species in open, high light sites (Mary Paezel, personal communication). Associated species include Psilocarphus spp., Allocarya spp., Polygonum spp., and Juncus balticus (California Natural Diversity Data Base).