. The Canadian field-naturalist. Natural history. Figures 13-16. Distributions of vascular plants in southern Ontario (based on herbarium specimens) in relation to lime- stone plains (shaded). 13. Gewn triflorum. 14. Bouteloua curtipendiila. 15. Carex crawei. 16. Ranunculus fascicu- laris. slacks as suggested by their southern Ontario distri- butions. Geranium carolinianum (Figure 17), Draba reptans (Figure 22), and Myosotis verna (Figure 18) grow on sandy flats and strands as well as on alvars. A less frequent alternative habitat is cliffs, particu- larly of dolomite and marble, which are the
. The Canadian field-naturalist. Natural history. Figures 13-16. Distributions of vascular plants in southern Ontario (based on herbarium specimens) in relation to lime- stone plains (shaded). 13. Gewn triflorum. 14. Bouteloua curtipendiila. 15. Carex crawei. 16. Ranunculus fascicu- laris. slacks as suggested by their southern Ontario distri- butions. Geranium carolinianum (Figure 17), Draba reptans (Figure 22), and Myosotis verna (Figure 18) grow on sandy flats and strands as well as on alvars. A less frequent alternative habitat is cliffs, particu- larly of dolomite and marble, which are the alterna- tive habitats of species such as Euphorbia commuta- ta (Figure 21) and Pellaea atropurpurea (Figure 19). Since more or less flat limestone shorelines exceeding 50 m in width and above the high water level are accepted as alvars here, a few species such as Hypericum kabnianum and Solidago spathulata are included within the group of confined species, but would be excluded if the definition was limited to only inland sites or more extensive shoreline exposures. Species with approximately 50% of their occur- rences on alvars, such as Bromus kabnii (Figure 6), Castilleja coccinea (Figure 8), , Rhus aromatica, Saxifraga virginiensis (Figure 4), and some species with less than 50% of occurrences on alvars such as Juniperus communis var. depressa, Shepherdia canadensis and Viburnum rafmesquianum, are nev- ertheless closely associated with the alvar landscape. In general, these species are frequent on alvars but also occur in other habitats that are common within or near to some of the alvar landscapes, such as fens, limestone rock exposures, granite balds with calcare- ous overburden, open calcareous sands, and open calcareous seepage slopes. Widespread species associated with the alvar landscape range from those that are locally abundant or even dominant on alvars such as Senecio pauper- cuhts (Figure 7) and Sporobohis heterolepis (Figure 12) to some that are uncommon and ge
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