Population biology and floral variation in Lythrum salicaria, a heterostylous colonizing weed.

Lythrum salicaria (purple loosestrife) is a Eurasian weed that was brought to eastern North America during the early 1800s. It is a perennial herb with tristylous flowers. Tristyly involves three reciprocal arrangements of stamens and styles: where the stigmas are respectively above (long-style), between (mid-style), or below (short-style) the two whorls of stamens. Tristyly in association with biochemical self-incompatibility promotes outcrossing in this species. The reproductive potential should be maximized when plants of the three flower morphs are present in equal proportions in a population. Seventy four populations of L. salicaria were surveyed from Windsor, Ontario, to the Gaspe peninsula in Quebec. Anisoplethy (unequal frequencies of the three morphs) was documented in 67% of these populations, including ten completely monomorphic or dimorphic populations. Morphometric analysis of flowers was conducted on samples collected from 49 populations. Traits studied included the length of calyx, length and width of petal, and lengths of stamens and pistil. Results indicated significant variability among genets, flower morphs and sites. Controlled field experiments were conducted using cloned genotypes of each of the three morphs, in transects of each of four soil moisture levels and each of three nutrient levels to test the effect of these two factors on patterns of clonal growth and reproductive morphology. Clonal growth was measured in terms of the number of ramets per clone, clone diameter and total length of ramets; an index of reproduction was recorded as the total length of infructescence per clone. The results demonstrated a highly significant effect of flower morph on clonal growth and on the index of reproduction. Significant effects of both soil moisture and nutrient level were observed on clonal growth. Soil moisture had a significant effect on the absolute dry mass of flower parts, but not on their pattern of proportional allocation. A controlled pollination experiment was conducted to test maternal and paternal success among flower morphs and genets. Factorial hand pollinations were carried out in a greenhouse, using four genets of each of the three flower morphs. Pollinations involved flowers with stamens and stigma of similar height (i.e., legitimate crosses), stamens and stigma of dissimilar heights between different morphs ( illegitimate intermorph crosses), between individuals of the same flower morph (intramorph), and stamens and stigma of the same flower (self). Legitimate pollinations yielded significantly greater seed set than any other pollination types. The three flower morphs differed significantly as maternal parents but not as paternal parents. However, there was also significant variation among genets as either maternal or paternal parent. The results showed weakest self-incompatibility in the mid morph, and strongest in the short morph. The effect of L. salicaria colonization on a native wetland species, Typha angustifolia, was tested in a field competition experiment using a modified replacement design. The experiment showed long-term superior competitive ability of L. salicaria, and suggests that caution should be taken before drawing long-term predictions from short-term competition studies. (Abstract shortened by UMI.)Dept. of Biological Sciences. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1996 .M35. Source: Dissertation Abstracts International, Volume: 59-08, Section: B, page: 3848. Adviser: Jon Lovett Doust. Thesis (Ph.D.)--University of Windsor (Canada), 1996