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COSEWIC Assessment and Update Status Report on the Scouler’s Corydalis in Canada

Biology

Scouler’s corydalis is a long-lived perennial, rhizomatous herb. Little is known of the species’ biology, specifically its longevity, methods of long-distance terrestrial dispersal, and interspecific interactions.


Life Cycle and Reproduction

Scouler’s corydalis reproduces asexually to form large clones, as well as sexually, with each flower in the raceme of 15–20 flowers having two carpels containing many seeds. Seeds are short-lived and desiccate quickly (Hartwell and Paige 2004).

Scouler’s corydalis begins flowering after four or more years of age. Flowering takes place in May and June in the Nitinat River watershed, and the plant becomes dormant by late summer. Both anthers and stigma are enclosed by the determinately shaped and arranged petals of Scoulers. Liden (1986) reports that most of the species in the tribe Corydaleae (to which Scouler’s corydalis belongs) are strongly self-sterile; Ryberg (1960) speculated that Scouler’s corydalis is very likely self-sterile, since the cultivated specimens from which he obtained ripe seeds did not produce fruits until individuals from two different clones were planted together. However, it is known that sometimes only the terminal flower of the raceme develops (Hitchcock et al., 1969), and this would severely compromise seed production. The species reproduces very well asexually by underground rhizomes and it is capable of sexual reproduction by seed.

Scouler’s corydalis produces annual stems apically from thick rhizomes that may also form horizontal stolons in older plants (see Ryberg 1960 for further details).

A number of pollinators visit Scouler’s corydalis, indicating that cross-fertilization probably occurs; however, recalling that few flowers develop, this may well not be an effective means of reproduction for the species.


Herbivory

Little is known about herbivory or grazing on Scouler’s corydalis. However, clipped stems, most likely the result of grazing by elk or deer, were observed occasionally during site visits by the authors in 2003. The presence of alkaloids in Scouler’s corydalis may reduce herbivory (Ownbey 1947). Few Corydalis species are eaten by deer, even in cultivated gardens where deer herbivory is high (D. Fraser pers. obs. 2006).


Physiology

The range of climatic conditions that Scouler’s corydalis can withstand is unknown. The successful method of asexual reproduction employed by Scouler’s corydalis may explain the species’ ability to dominate large areas of shady floodplains. The species appears to be highly shade tolerant and does not seem to have specific edaphic requirements. It thrives in cultivation without specific treatment other than moisture and shade; however, limiting factors in the wild may constrain habitat suitability.


Dispersal

Periodic flooding may facilitate seed or rhizome dispersal, and may play a critical role in dispersal, as evidenced by the appearance of clustered subpopulations along streams and rivers. In addition, the obovoid, bicarpellate seed capsules separate elastically when jarred even slightly, which can scatter seeds up to two metres.

Ants are likely a viable short-range dispersal agent for seed of Scouler’s corydalis. The seeds of Corydalis species, including Scouler’s corydalis, have appendages called elaiosomes that contain lipids, proteins, sugar, and vitamins, a valuable nutritional source for ants. Although there is no known research on Scouler’s corydalis dispersal, Ohkawara et al. (1997) report dispersal of seeds by ants for C. ambigua , and Hanzawa et al. (1985) report this for C. aurea as well. Ohkawara et al. (1997) found that the mean dispersal distance of Corydalis ambigua seeds by ants was up to about 80 cm. Hanzawa et al. (1988) demonstated that dispersal by ants of Corydalis aurea seeds can increase population growth rate. In an earlier paper, Hanzawa et al. (1985) reported that the elaiosomes on the seeds of Corydalis aurea are attractive to ants, but repulsive to the deer mouse(Peromyscus maniculatus ), a seed predator. This mouse is also found on Vancouver Island.


Interspecific Interactions

Interspecific interactions other than pollinators and dispersers for Scouler’s corydalis are unknown.


Adaptability

Scouler’s corydalis’ adaptability is not known, although it can be raised horticulturally given the appropriate shade and moisture conditions. The species appears to be well adapted to flooding disturbance due to its proximity to the rivers and channels of the Nitinat, Klanawa and Carmanah river valleys. It may even require periodic flooding to maintain or create habitat as well as to aid in dispersal. Scouler’s corydalis’ tolerance to other types of disturbance and degradation is unknown. However, plants at the Cowichan-Nitinat junction are growing, and flowering, within a metre of the heavily used roadway. In addition, several populations near roads can be covered in thick layers of dust, as observed by the authors in 2003, and show no noticeable loss of vigour. Other populations are growing in roadside ditches that are periodically cleared to improve drainage. Such clearing could either create habitat or become a threat to the population depending on how often the ditch clearing was done.

It is not known why this species has such a limited distribution on Vancouver Island.