Geological Influence on the Distribution of Pink and Yellow Lady’s Slipper Orchid
One of the first plant distribution patterns I learned was that pink lady’s slipper orchid (Cypripedium acaule) grows on acidic substrate, like granite rock and derived soils, and yellow lady’s slipper orchid (Cypripedium parviflorum) grows on calcareous substrate, like limestone rock, and derived soils (Photo 1).
Photo 1: The general observation that pink lady’s slipper orchid (Cypripedium acaule) grows on acidic substrate, like granite, and yellow lady’s slipper orchid (Cypripedium parviflorum) grows on calcareous substrate, like limestone.
Orchid Distribution
Consider the distribution of these orchids in eastern Ontario (Photo 2; iNaturalist data, Sept 2020). Most C. acaule are located north of the heavy line, where as most C. parviflorum occur south that line. The separation is not perfect, but the general pattern is suggestive.
Photo 2: The distribution of pink lady’s slipper orchid (Cypripedium acaule), on the left, and yellow lady’s slipper orchid (Cypripedium parviflorum), on the right, based on data from iNaturalist, September 2020. Most C. acaule are located north of the heavy line, where as most C. parviflorum occur south that line. The separation is not perfect, but the general pattern is suggestive.
Simple Bedrock Geology of Southeastern Ontario
There is a coarse geological influence on the distribution of these two orchids. Let us consider the general geology of eastern Ontario (Photo 3). The rocks that under areas “A” and “B” are part of the Canadian Shield. These ancient rocks are considered to be “acidic” in floristic systems.
Photo 3: General bedrock geology of eastern Ontario. Area “A” is the Canadian Shield, which consists of range of rock, many of which are considered to be acidic (pink, red, and brown colour on the image). Area “B” is also part of the Canadian Shield, but marble rocks are common (blue) Marble is a limestone that was cooked deep below the Earth’s surface. Area “C” consists of limestone, dolomite and shale rocks (blue, pale yellow and pale green colour on the map). Note, there is a small area limestone and dolomite rock, similar to the rocks in southern Ontario, but located in the Temiskaming Shores area, Area “C” consists of younger limestone, dolostone, and shale rocks that occur mainly in southern Ontario, with a small area located around Temiskaming Shores. Area C rocks are considered to be limy, calcareous rocks. The general geology from Ontario Geological Survey, OGSEarth on-line geological data.
Area “B” is also part of the Canadian Shield, but there is a lot of ancient marble in the package of rock. Marble is limestone that was cooked and squeezed deep below the surface of the Earth. Marble, like limestone and dolostone, is a limy, calcareous rock. Because of the abundant marble, the vast parts of substrate of Area “B” differ from that of Area “A”. Area “B” is calcareous, whereas Area “A” is considered to be mostly acidic.
Area “C” consists of younger limestone, dolostone, and shale rocks that occur mainly in southern Ontario, with a small area located around Temiskaming Shores. Area “C” rocks are limy, calcareous rocks. Note that rocks typical of those found in Area “C” also occur in the James Bay and Hudson Bay lowlands, not illustrated on this figure.
Bedrock Geology and Orchid Distribution
Most vast areas underlain by limestone and dolostone rocks occur in southern Ontario and in the Hudson Bay and James Bay lowlands. BUT, there are exceptions!
Exception “1”: C. parviflorum occurs in the Temiskaming Shores area, where limestone and dolomite rock are common (see tiny blue area marked limy on Photo 3). The Temiskaming Shores area geologically resembles southern Ontario. There are other exceptions across northern Ontario, some of which may be, or can be, attributed to the presence of local soils composed of calcareous clay and other glacial deposits derived from the limestone rocks of the James Bay lowlands. The Fraserdale area, in northern Ontario, is an example of the influence of glaciation on the limy nature of glacial deposits.
Exception “2”: C. acaule occurs in the Pinery Provincial Park area, where limestone rock is common adjacent to Lake Huron. Wasyl Bakowsky reminded me that the Pinery area is dominated by sandy pine woods. Conifer needle litter leachate is acidic, which creates an acidic, upper soil layer, despite the calcareous sands. I suspect that other exceptions in southern Ontario are also attributed to local acid leachate.
Summary
Some broadly regional geological patterns influence the location and distribution of some plants. The broadly regional distribution of acidic rock, like granite, and limy calcareous rock, like limestone and dolostone, influences the distribution of Pink Lady’s Slipper (Cypripedium acaule), which tends to grow on acidic substrate and Yellow Lady’s Slipper (Cypripedium parviflorum), which tends to grow on limy, calcareous substrate.
Sept 13/21; Nov 16/21