Title

Functional ecology of gender change in {\it Arisaema triphyllum\/}: An interdisciplinary approach

Date of Completion

January 1997

Keywords

Biology, Botany

Degree

Ph.D.

Abstract

Arisaema triphyllum is a diphasic (gender-switching) geophyte that is common in New England forests. It is commonly understood to be female when large and male when smaller. The smallest individuals are usually vegetative. A reciprocal transplant experiment was set up to determine if local differentiation for the gender switch-point has occurred between local populations in Connecticut. We found that stem diameter is a better predictor of gender than is leaf size. Using stem diameter as the measure of size, we have been able to determine that there is some evidence of local differentiation. The functional relationship between size and gender relationship is further complicated by the architecture of this species, which reveals a morphological basis to the lag effect. The lag effect refers to the finding that size and reproductive status in one year, may have a significant effect on size and reproduction in subsequent years.^ Preformation of inflorescences is likely to be common in spring-flowering geophytes. Initiation of leaves and reproductive organs in the year prior to expression may allow such species to emerge and flower before canopy closure, as well as before competition for light among herbaceous species becomes a factor on the forest floor. Arisaema triphyllum has preformed inflorescences which may be either male or female. Plants emerge and flower in mid-May to early June. Initiation of the next year's reproductive apex occurs in mid- to late June or early July. Male and female inflorescences can be distinguished by mid-July. All floral primordia are fully initiated by mid-August. At this point, the above-ground shoot has finished flowering and female shoots are provisioning the developing embryos. Seeds on the current aerial shoot mature in mid-September. Thus, reproductive decisions for the following year are made just after flowering and prior to seed set. Shoots of the current year have no internodal elongation, and the basal portion is expanded into a corm. This corm is absorbed as the current aerial structures expand. In reproductive plants, a new corm is produced sympodially in June, prior to the initiation of new floral axes. ^