Ecological variation in Aconogonon weyrichii was studied at 3 sites. Comparisons of morphological characteristics were done at an open highland site, an open lowland site and an alder-forest site, Biomass and resource allocation comparisons were done at the open lowland site and the alder-forest site. Both open sites had oligotrophic mineral soil with low vegetation cover, whereas the forest site had eutrophic organic soil with high vegetation cover. Morphological characters were relatively similar at both open sites, and A. weyrichii populations had the same life-cycles. At the forest site, A. weyrichii was much larger in size and biomass than that at the lowland open site. The open site type had very deep vertical rhizomes which produced aerial shoots at the same locations every year. The forest site type had very dense and dynamic horizontal rhizomes which had many dormant buds, and actively produced large, dense ramets. The open site type allocated much resource expenditure to flower production, whereas the forest site type allocated much resource expenditure to aerial stems. High resource allocation to aerial stems and rhizome differentiation (vertical vs. horizontal) relative to forest type are adaptations which enable A. weyrichii, originally growing at unstable open sites, to grow in the alder-forest.
