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Bidens amplissima in Washington State

Peter Zika of Washington Sate has found Bidens amplissima in Washington State near a historical site in Everett.  Good going Peter!  Contact info: Peter Zika (2004)

Bidens amplissima at Rithet's Bog

Submitted by Sharon Hartwell  August 12, 2004

In the fall of 2002, at Rithet's Bog in Victoria, as part of a restoration project with Ducks Unlimited, several hectares of willow were cleared from the Chatterton field, and a weir was installed at the outlet to the bog. As a result, there is a seasonal wetland on the Chatterton field, and the Dalewood field (north side of the bog forest) also stays wet for a longer period of time, although the standing water does not persist, with mudflats appearing by April.

Last year [2003], B. amplissima had spread throughout the entire Chatterton field, primarily on the peripheral areas where the water first dropped, but the main concentration of plants was still in the pond area to which it had formerly been restricted. Almost 500 plants were counted. Only B. cernua was found on the Dalewood fields.   This year, due to the late rains in May and last week, we have quite a different situation. The water levels are much higher, and 20% of the Chatterton field still has standing water. There are some large and vigorous B. amplissima,but they are restricted to the periphery of the field. The former Bidens pond area is still full of water.

However, the Dalewood field is a different story. It has been disappointing to bird watchers because the open mud flats became vegetated, and it was no longer a hot spot for shorebird viewing. What you see now is dense stands of Bidens amplissima, forming a sea of yellow over several patches, the largest of which is ca. 100 metres by 8 metres, and is almost all B. amplissima, mixed with some B. cernua. There are thousands of plants, the most robust of which are over 5 feet tall. It actually forms what you might call an annual wetland community. A series of smaller patches also exist, some of which are B. cernua, some pure B. amplissima, and some mixed. If hybridization occurs, then there are bound to be some hybrid plants as well.  Many of the plants in these smaller patches are heavily infested with a small leaf beetle, Calligrapha californica ssp. coreopsivora (Matt Fairbarns noted this beetle at Somenos Marsh last year) B. cernua seems to be most heavily infested, to the point of total defoliation. In many cases it is difficult to tell the cernua from the amplissima.  The infested plants are much smaller - only 18" tall in most cases.   This is such a dramatic change in the size, location and composition of the [Bidens amplissima] population, and a graphic illustration of how rapidly annual species can exploit new habitat! Also illustrates the need for annual monitoring (both senses of annual!).