Date of Award

Winter 1983

Project Type

Dissertation

Program or Major

Botany

Degree Name

Doctor of Philosophy

Abstract

Ruppia maritima L. populations in coastal and estuarine tidal marshes in New Hampshire exhibit considerable variation in morphology, reproductive strategy and pollination ecology in response to a range of environmental conditions. Variation among the populations correlates with seasonal changes in environmental conditions recorded at various sites. A comparison of coastal and estuarine habitats of Ruppia has shown them to differ significantly with respect to such factors as: origin and development, substrate, epibiota, floristic and faunistic components and seasonal patterns in water depth, temperature and salinity. The three varieties Ruppia maritima L. occurring in New Hampshire are phenotypically plastic in response to the seasonal environment in ecologically distinct habitats. Phenotypic plasticity, however, accounts for only a part of the variation exhibited by Ruppia populations. Genotypic differentiation has occurred and populations characterized by a particular reproductive strategy and morphology may be genetically discrete. The adaptive significance of phenotypic plasticity and genetic variation relative to seasonal periodicity and phenological phenomena in Ruppia populations is discussed. A reciprocal transplant field study and a controlled environment greenhouse experiment contribute to an assessment of autecological data. Morphological variation in vegetative organs, reproductive parts and in the pollen was observed.

Coastal and estuarine populations were examined and compared for several ecological, phenological and reproductive criteria. Coastal populations are biennials or short-lived perennials producing relatively little seed; pollination occurs at the surface of the water facilitating an out-crossing strategy. Estuarine populations are for the most part annuals producing abundant seed; an underwater pollination mechanism promotes selfing. The physiology of the underwater pollination mechanism is documented by anatomical evidence and time-lapse cinemicrography. The sediments in most of the study areas contain a seed bank although the seed concentration is higher in the estuarine habitats. A seed bank provided for the reestablishment of large populations of Ruppia at several locations which had been devoid of plants for one or two years. Chromosome numbers, however, indicate polyploidy in the coastal populations where 2 n = 28 while the estuarine populations were found to be 2 n = 14. Implications of variation and reproductive biology in Ruppia relative to its taxonomy are discussed.

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