. The Canadian field-naturalist. 460 The Canadian Field-Naturalist Vol. 87 Vegetative Distinctions in Canadian Species of Mitella and Tiarelld Abstract. Petiole hair characters serve to separate foliage of Mitella diphylla (miterwort) and Tiarella cordifolia (foam flower), help to separate the five species of of Mitella in western Canada, and demon- strate introgression between Tiarella laciniata and T. trifoliata more clearly than does leaf shape. The host plants of rust fungi are often not reliably determined. Sometimes the specimens are collected late in the season when flowers or fruit are
. The Canadian field-naturalist. 460 The Canadian Field-Naturalist Vol. 87 Vegetative Distinctions in Canadian Species of Mitella and Tiarelld Abstract. Petiole hair characters serve to separate foliage of Mitella diphylla (miterwort) and Tiarella cordifolia (foam flower), help to separate the five species of of Mitella in western Canada, and demon- strate introgression between Tiarella laciniata and T. trifoliata more clearly than does leaf shape. The host plants of rust fungi are often not reliably determined. Sometimes the specimens are collected late in the season when flowers or fruit are scarce; but often the collector, through over- confidence in his diagnostic ability, simply omits flowers or fruit that may occur. In a current re- vision of some rusts of Saxifragaceae I found reason to doubt the names applied to various Mitella and Tiarella specimens. The leaves of phanerogamic specimens of the species in ques- tion were accordingly examined in a search for new characters. The petiole hairs proved to pro- vide such characters. The findings are presented here as an aid to mycologists, ecologists, or others who may need to identify vegetative material. In eastern Canada Mitella nuda is confined to the boreal forest. Thus the only serious problem is to distinguish M. diphylla and Tiarella cordi- folia, which have a broad ecogeographic overlap in the hardwood forests. The leaves of T. cordi- folia tend to have more rounded teeth and to con- tain more anthocyanin than those of M. diphylla; but these variable characters are of little help if the plants are not associated. Examination of numerous sheets of both species from Ontario and Quebec, and of shorter series from the rest of their ranges, showed that their petiole pubes- cence is consistently distinct. Adjacent to the blade the distinctions are not always sharp, but near the middle of the petiole they are strong and constant. The hairs of Tiarella cordifolia grade imper- ceptibly from sessile or subsessile r
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