Alkali Marsh Butterweed, Alkali Marsh Ragwort, Great Swamp Groundsel, Water Groundsel, Water Ragwort: Senecio hydrophilus (Synonym: Senecio hydrophilus var. pacifica)

The photo above shows a close-up of one cluster of flower heads of great swamp groundsel as seen near French Glen, OR (southeastern Oregon)..........July 30, 2004. Note the narrow disks and the several short ray flowers.

Great swamp groundsel is a hollow-stemmed perennial arising from 40-200 cm in height from stout rootstocks. The stout stems arise singly or in small clusters. The herbage is smooth and often glaucous or bluish tinged. The succulent leaves are thick and firm with entire to serrate margins. The lower leaves are long-petioled with a long, narrowly elliptic blade from 10-20 cm long and 2-5 cm wide. The stem leaves are reduced in size and become sessile. They 4-10 stem leaves are narrowly lanceolate and taper gradually to the tip (as seen in the photos on this page) upwards on the stem.

The flower heads are numerous and crowded, forming either a tight cluster or a broad corymbiform panicle. The flower heads may be entirely disk flowers, or may consist of both ray and disk flowers. When present, the 5-10 rays are yellow and 4-8 mm long. The disk is narrow. The involucre is 5-8 mm tall with 17-21 narrow, black-tipped bracts.

Great swamp groundsel is found in wet, swampy places at low elevations which often dry by mid-season. It is tolerant of alkali conditions.

Great swamp groundsel is found from British Columbia to California, and east to Montana, South Dakota, and Colorado.

In the Columbia River Gorge, it is found at river level from west of Bonneville Dam.

Alkali marsh butterweed as seen in the vernally inundated meadows at Panakanic in western Klickitat County..........May 17, 2013 (left) and June 17, 2013 (right). Note the fleshy leaves in the photo at left.

Close-up views of the upper stem, seed heads and stem leaves of alkali marsh butterweed as seen from the shores of the Columbia River near Dalton Pt.........October 1990 for the photo at left and August 19, 2009 for the three photos at right.

The basal leaves of alkali marsh butterweed as seen on a sandy point along the Columbia River shoreline about one-quarter of a mile west of the Dalton Point boat landing............October 8, 2012.

The photo above shows a cluster of great swamp groundsel as seen near French Glen, OR (southeastern Oregon)..........July 30, 2004. Note the glaucous cast to the leaves and the long petioles and broadly elliptical blades of the lower leaves.

The photo above shows several of the lower leaves of great swamp groundsel as seen near French Glen, OR (southeastern Oregon)..........July 30, 2004. Note the glaucous cast to the leaves and the long petioles and broadly elliptical blades of the lower leaves. The lightly toothed margins can also be seen.

The photo above shows a stem leaf of great swamp groundsel as seen near French Glen, OR (southeastern Oregon)...........July 30, 2004. Note the sessile base, minutely toothed margin, and that the blades are widest at the base, tapering gradually to the tip.