. The Canadian field-naturalist. 164 The Canadian Field-Naturalist Vol. 94. Figure 1. Selected locations of Isoetes eatonii showing typical range of distribution for this species (see Appendix for collection data). Towards the end of the growing season the yellow- ing leaves become limp and lie flat on the substrate, losing their upright, quillwort appearance. In late fall the leaves break away from the plant easily, differing from some other species in eastern Canada (/. echi- nospora and /. macrospora) which tend to have some green leaves that remain with the plant during the winter. Where l
. The Canadian field-naturalist. 164 The Canadian Field-Naturalist Vol. 94. Figure 1. Selected locations of Isoetes eatonii showing typical range of distribution for this species (see Appendix for collection data). Towards the end of the growing season the yellow- ing leaves become limp and lie flat on the substrate, losing their upright, quillwort appearance. In late fall the leaves break away from the plant easily, differing from some other species in eastern Canada (/. echi- nospora and /. macrospora) which tend to have some green leaves that remain with the plant during the winter. Where leaf morphology can be variously and some- times very severely affected by environmental factors, such as water depth, or water flow, spore characters are the most reliable features in determining some species of Isoetes. The sculpture of the megaspore of this species in the original description of Dodge (1897) is given as "labyrinthiform-convolute" and later described by Pfeiffer (1922) as "with irregular commissural ridges and with faces marked very irregularly by crowded short meandriform elevations, sometimes with round- ed ; With the aid of the SEM (Scanning Electron Mic- roscope) the megaspores are seen to have an appear- ance of brain coral, with short ridges and mounds (Figure 2A), all of even height, closely crowded and having a secondary texture of fine spines on these ridges or mounds (Figure 2B). These features compare well with SEM results of type material (Figure 2C) and with other material of /. eatonii from the north- eastern United States. The microspore walls appear variable from almost smooth to slightly papillose or even with low widely spaced, thick-based spines (Figure 2D). In the standard manuals used for species identifica- tion (Fernald 1950; Gleason 1968; Wherry 1972) Isoetes spores are always represented by drawings which, at times, are subject to the artists' own interpre- tations of the spore coat sculpturing, resulting in d
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