Scouler’s corydalis (Corydalis scouleri) COSEWIC assessment and status report: chapter 2

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Species Information

Scouler’s corydalis is a tall perennial herb with thick rhizomes. Stems are hollow, simple or somewhat branched above and 40–120 cm tall. The blue-green, glaucous (white to blue waxy powder) leaves are usually three in number, from near or above the middle of the stem. The lower one is often 20–30 cm long. The terminal inflorescence, appearing in May and June, is usually a compound raceme (an elongated inflorescence with youngest flowers at the tip) of 15–20, spurred, rosy-pink flowers.

Distribution

Scouler’s corydalis occurs west of the Cascades Mountains (mostly coastal) from north-western Oregon northward through Washington’s Olympic Peninsula to south-western Vancouver Island. In Canada, C. scouleriis found only in south-western British Columbia. Sites are limited to the Carmanah Creek (new since the 2000 status report), Cowichan Lake, Klanawa River and Nitinat River drainages. The Canadian populations are located about 80 km north of the Washington populations of the Olympic Peninsula. Since 2000, the extent of occurrence has increased from 250 km²to 275 km² due to additional search effort. However, due to limited road access to potential habitat for this species, a significant area of potential habitat remains unsearched at this time. The estimated further potential extent of Scouler’s occurrence is an additional 825 km² if potential habitat in the Walbran and Cowichan Lake drainages is considered.

Habitat

Lush stands of Scouler’s corydalis are found in wet, cool habitats associated with watercourses – ranging from large rivers to small tributary streams. Elevations range from sea level to almost 200 m on southwestern Vancouver Island, British Columbia. The species occurs on gradually sloping alluvial floodplains and river terraces within early seral mixed or deciduous forest habitat and rarely in coniferous stands. Of the Alnus rubra stands surveyed in the Nitinat River Valley of approximately 30 years old and older, all were found to contain C. scouleri. Scattered individuals are also found on road edges, ditches, clearings and other human-modified habitats.

Biology

Scouler’s corydalis is a perennial herb producing annual stems apically from thick rhizomes. Seedlings have a rather thick taproot, which probably remains at least until the plant reaches flowering age, and very likely much longer. Older specimens have only annual adventitious roots that originate in the spring just below the aerial part of the shoot.

Population Sizes and Trends

There are presently 24 known populations where Scouler’s corydalis has been observed in British Columbia within the last six years (1997 to 2004). Since 2000, new inventory has increased the number of known stems from 117 395 to 848 000 stems. Due to the nature of the growth habit of this species, it is not known how many stems make up an individual. For individual populations, stem numbers range from one up to 462 000. Seven of the populations have stem numbers over 20 000, which represent over 95% of all the stems in British Columbia. The extent of stems at the sites varies greatly in size from just a few square metres to 3.4 ha. Eight of the populations are over 0.5 ha in size. The total area currently occupied by these populations is 0.10 km².

Limiting Factors and Threats

Current potential threats to Scouler’s corydalis, from logging, road and bridge building, recreational use and natural flooding are probably minor. These threats will have less impact on the total populations of Scouler’s corydalis since there are now known to be over 800 000 stems over a 275 km² area. As well, Wildlife Habitat Areas prohibit logging, road and bridge building within the designated wildlife areas which protect over 400 000 stems. Road building and bridges have damaged some Scouler’s corydalis populations in the past; however, the total percentage of the population removed has been low (less than 2%). Some riverbank damage occurs when recreationalists have easy access to the rivers, but this is very minor at this time. Natural flooding, from time to time, removes riverbanks and floodplain populations resulting in only temporary population reduction because the flooding creates new habitat and could possibly provide a dispersal mechanism.

Special Significance of the Species

Scouler’s corydalis, along with a number of other Corydalis species, is well known in the horticultural trade. In addition, the alkaloidal properties of a large number of members of both the Fumariaceae and the closely related Papaveraceae (poppy family) are of great interest to plant taxonomists, plant chemists, and agronomists.

Existing Protection or Other Status

Scouler’s corydalis could be a candidate for protection in British Columbia under the provincial Wildlife Amendment Act 2004 as it is currently blue-listed by the provincial Conservation Data Centre and on the federal Species at Risk Act Schedule 1. The species was assessed as Threatened by COSEWIC in 2001. Three of the Scouler’s corydalispopulations in British Columbia are protected by the Provincial Park Act since they occur in two Provincial Parks and an Ecological Reserve covered by the Ecological Reserves Act. The Forest and Range Practices Act (FRPA) of British Columbia identifies conservation and management issues, including Wildlife Habitat Areas. Scouler’s corydalis is presently listed under the Identified Wildlife Management Strategy under the Government Actions Regulation of FRPA. Wildlife Habitat Areas have been officially designated under the British Columbia Forest and Range Practices Act for eight of the populations in the Nitinat River drainage. This includes sites with approximately 437 100 stems protected through this means. These Wildlife Habitat Areas are to be managed for Scouler’s corydalis. Although not stated in the original status report, populations of the species occur within a Provincial Park (44 850 stems) and an Ecological Reserve (less than 15 stems).

Under the Forest and Range Practices Act, larger fish-bearing streams such as the Nitinat, Klanawa and Carmanah-Walbran are managed under a default standard that requires a Riparian Reserve zone associated with a Management zone. As such, licensees can be encouraged to leave the management zones intact and associate their wildlife tree retention to help protect and buffer potential habitat for Scouler’s corydalis within these areas.

In addition, both Western Forest Products and Teal Jones have recorded the British Columbia Conservation Data Centre information for Scouler’s corydalis in their GIS systems and have referred to the data for tree harvest planning.