A comparative study of spore germination of some Isoetes species of northeastern North America

Abstract

Germination of megaspores and microspores of five Isoetes species is described. Under laboratory conditions spore samples were subjected to cold, cool, and warm temperatures for 12 weeks to establish the role of these conditions on the subsequent percent germination and the rate of germination. It was found that taxa with higher chromosome numbers (decaploid, I. macrospora; tetraploids, I. tuckermanii and I. riparia) showed higher overall megaspore germination in the 70-day test period, for both cold and control samples. Microspore samples under the same temperature regimes had higher overall germination amongst tetraploid species. Results also showed that I. macrospora and I. tuckermanii megaspores germinated without a cold pretreatment, while I. acadiensis, I. riparia, and I. echinospora required a cold period to germinate. Microspore samples of I. echinospora (diploid) did not need to be treated with cold to germinate but the rate and final percent of germination was greatly increased if the spores were subjected to cold first. Isoetes riparia microspores required a cold period for germination while those of I. tuckermanii and I. macrospora did not. The cold period served to delay germination of microspores of both of these species during the cold period and also for some days afterwards. The germination data on both types of spores in these laboratory conditions showed interesting time correlations of behaviour between the microspores and megaspores of each species.