. The Canadian field-naturalist. Natural history. 568 The Canadian Field-Naturalist Vol. 116 energies into the rapid production of sexually pro- duced propagules. Whetlier, like some Tolypellas, it can also behave as a winter annual is not known. Its growth in ephemeral habitats as individual scattered plants arising from a single rhizoidal node also sug- gests its annual nature. No evidence of clonal growth has yet been noticed. Distribution Nitella macounii was first collected at Niagara Falls, Ontario, in 1882, and including Crum's (1975) reports, only 12 collections were known until the fo
. The Canadian field-naturalist. Natural history. 568 The Canadian Field-Naturalist Vol. 116 energies into the rapid production of sexually pro- duced propagules. Whetlier, like some Tolypellas, it can also behave as a winter annual is not known. Its growth in ephemeral habitats as individual scattered plants arising from a single rhizoidal node also sug- gests its annual nature. No evidence of clonal growth has yet been noticed. Distribution Nitella macounii was first collected at Niagara Falls, Ontario, in 1882, and including Crum's (1975) reports, only 12 collections were known until the four reported in this paper. The general distribution is centered in three major areas, the Great Lakes of southern Ontario, northern Iowa/north-eastern South Dakota, and south-central Saskatchewan as illustrat- ed in Figure 3 (G. Allen 1954; Crum 1975). Current records from Saskatchewan are in excess of 800 km from the closest South Dakota collections and 1900 km from the nearest Canadian site. In this study and also that of Crum (1975) C. braunii is very often a companion of N. macounii. Assuming equal dispersal capabilities, why then are the ranges of the two species so different? C. braunii occurs right across the continent from southern Canada to Mexico, whereas N. macounii is restricted to a small region of the north-central continent. One part of the answer, no doubt, is that C. braunii has a broader ecological tolerance to biotic and/or abiotic conditions, but exactly what these are is not known at present. Another conjecture is that A^. macounii is a relatively recent disjunct immigrant from South America, the result of an uncommon long distance dispersal event, and is now undergoing adaptation and dispersal in its new Figure 3. Distribution map of N. macounii. Each number refers to the number of individual collections from the region. A third possibility, highly probable, is that N. macounii is in fact more widely distributed across the continent than
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