Dear Doug. Thanks for your report of Orange Jewelweed. I will share your report with the City of Eugene who manages the Delta Ponds. Orange Jewelweed is a non native invasive species that often does not get the attention it deserves. Many mistake it for a native species. I asked Dominic Maize at Portland Bureau of Environmental Services about the status of this plant and here is what he said (with some minor edits by me):

" I. capensis is everywhere. Peter Zika has a paper from 2006, mentioning the interesting history of how this species was considered native; basically confusion with native Impatiens and taxonomy of the genus in general. Here is his paper in a nutshell at BEN (down a bit on the page):
http://www.ou.edu/cas/botany-micro/ben/ben408.html

Confusion still abounds; read this from the BPOTD at Univ. of BC in Canada, written by botany professors (and see Ed Alverson’s comments at the bottom of the page):
http://www.botanicalgarden.ubc.ca/potd/2010/10/impatiens_capensis.php

I see this species in practically every riparian corridor I visit up around the Portland area, which I am new to. Never saw all that much around the mid-Valley but that is likely to change. One exception: I visited Champoeg State Park when I first moved here in 2005 and was blown away by density oft his plant there. The dominant understory along those steep, eroded banks of the Willamette at that park? I. capensis. Bruce Newhouse has an observation from around Eugene from the 90’s, I think. As Zika points out, there are no observations/collections from before the 50’s in the NW; quite unlikely for so charismatic a plant.
So what’s the big deal? This species (and some other congeners) dominates riparian understories, shading out native forbs and outcompeting for pollinator services (as also documented with I. glandulifera in Germany). The big problem is that they are annuals: come fall this massive amount of biomass melts away and exposes bare soil=erosion=reduced water quality, salmonid habitat, etc. "

Thanks again Doug. Keep up the reports!

Tania


Tania Siemens
WISE Program Coordinator (Watershed and Invasive Species Education)
Oregon Sea Grant Extension
Oregon State University
tania.siemens@oregonstate.edu
541-914-0701

Tania Siemens
Aug. 25, 2011, 4:42 a.m.