Yellow montane violet (Viola praemorsa) COSEWIC assessment and status report: chapter 6

Biology

General

There is relatively little published literature on the biology of yellow montane violet. The following section draws heavily upon unpublished data from the author’s ongoing phenological study of yellow montane violet in British Columbiaexcept where otherwise noted. There is no information available on pharmacological or ethnobotanical uses of this species.

Life cycle and reproduction

Shoot dormancy begins to break in March when the soil begins to warm up with the spring weather. Plants are fully leafed out by late April or early May. Foliage begins to wither by mid- to late June and the shoots die back by mid- to late July as the summer drought deepens.

Plants may become large enough to flower within 2 years under favourable conditions, but more often they grow for several years before reaching flowering size. The average age of mature plants in Canada is unknown, but probably lies between 3-6 years. Chasmogamous flowering (flowers open for cross-pollination) occurs in late April and May and cleistogamous flowering (flowers remain closed and self-pollinate) occurs somewhat later. Chasmogamous flowers are rarely produced in late May or June but cleistogamous flowers continue to develop as long as the plants remain green. Most flowering plants produce 1-3 chasmogamous flowers and 0-5 cleistogamous flowers. Fruit dispersal occurs in June and July and all seeds are released by late July. The drying capsules rupture abruptly as they dry out, explosively dispersing seeds as much as 1 metre. Capsules produce an average of 8.8 seeds. Most early-developing seeds are well-formed and preliminary observations suggest that seed viability appears to be quite high. The seeds are hard and shiny and bear pale terminal fat bodies (elaiosomes) at either end. Pale, unfilled seeds are often present, especially in late-maturing capsules (pers. obs.).

The production of both chasmogamous and cleistogamous flowers may be a bet-hedging technique. Chasmogamous flowers enable a higher degree of recombination that may limit inbreeding depression. Cleistogamous flowers, which form later in the season when unpredictable rains may extend the life of a plant, may greatly increase fecundity by avoiding the high resource and time demands involved with the production of showy flowers.

The arrangement of the flower parts is such that most flowers are fertilized with pollen from other flowers, either on the same plant or from another (Baker 1935, Beattie 1969). Yellow montane violet is probably pollinated by the same species that pollinate closely related violets: flies, butterflies, solitary bees and thrips (Baker 1935, Beattie 1974 and Davidse 1976).

The elaiosomes are attractive to ants, which have been shown to disperse seeds of similar violet species over distances of 50 cm or more. Ant dispersal increases the overall dispersal distance of seeds (Ohkawara and Higashi 1994) and seeds in ant nests tend to have significantly higher germination rates (Culver and Beattie 1980). In another violet species, seeds from cleistogamous flowers tended to have slightly lower fitness than those from chasmogamous flowers but this is balanced by the much lower cost of production (Berg and Redbo-Torstensson 1999).

Yellow montane violet is incapable of clonal growth by asexual reproduction.

Herbivory

Insect herbivory is often observed on the leaves of British Columbia plants but damage is usually slight. Chasmogamous flowers are also sometimes damaged by insects (pers. obs.).

Livestock and wildlife grazing does not seem to cause a significant amount of direct damage. Grazing may reduce competition from taller-growing herbaceous and shrubby species but also appears to facilitate invasion by non-native grasses and forbs. Yellow montane violet avoids high competition environments by growing in areas with low biomass and/or by completing much of its life cycle before the biomass of more competitive species peaks.

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