Fifty ferns have been recorded from Grey and Bruce counties, two thirds of the fern flora of Ontario and only two fewer than the number found in the British Isles. Although the number is not great, people find them difficult to identify since they are all green and have no flowers.
The first identifying feature to view is the shape of the frond (leaf). In a few ferns the fronds are entire. A good example of this is the Hart’ s Tongue Fern. This is globally rare as, in North America, it is only found in any quantity in this area of Ontario, especially along the escarpment. There are a few remnant populations in the States. It is related to the much more common Hart’s Tongue found in Europe but, separation for thousands of years – probably by glaciation – has caused the North American population to develop into a separate sub-species.
In the picture of the Hart’s Tongue Fern, another fern can be seen just left of the centre which has the blade of the frond divided into leaflets. In ferns, these are called pinnae (singular – pinna). We refer to these ferns as once divided. This is the Northern Holly Fern so called because the pinnae are stiff and feel prickly. Another example of a once divided fern is the Polypody. This is not too common in this area as it flourishes in more acid situations but it will grow on a rock if it is covered with a good layer of humus and mosses.
The Walking fern is also an example of a fern with an undivided frond. In this case, they are very tapered and have the ability to root at the tip. Consequently, it forms dense clones. These are only found on the top of large dolostone blocks in this area.
In the Sensitive Fern the pinnules are indented but not quite divided into sub-leaflets. The Sensitive Fern is named because it is extremely sensitive to frost so that its fronds are one of the first to die and shrivel up at the beginning of autumn. In some ferns the second division is complete and the pinnae are divided into pinnules. We refer to these as twice divided. The Silvery Glade Fern is an example of this and so is the Virginia Chain Fern.
In some ferns the pinnules are further sub-divided into lobes and these are said to be thrice divided. A common example of this type of lacy fern is the Spinulose Wood Fern found in swampy forest. The Evergreen Wood Fern is similar but is found on drier forest floors, especially at the base of trees. Its fronds stay green all winter, even under the snow. The Lady Fern is also thrice cut. It is difficult to separate them until you turn them over and look at the way the sporangia (spore producing organs) are housed in the indusia. In the Spinulose and Evergreen wood ferns the indusia are little dots, in the Lady Fern they are slits which form chevrons. In the photo of the Virginia Chain Fern we are looking at the underside of the frond and we can seen the indusia tightly packed along the midrib.
There is a great deal of variation in the spore bearing organs of ferns. In some cases, like the Cinnamon Fern on the front cover of The Ferns of Grey and Bruce , the fertile frond is a totally different structure from the sterile fronds. The Cinnamon Fern is so named because the colour of the spores makes the fertile frond look like a cinnamon stick. The Sensitive Fern also has a different kind of fertile frond which remains erect and shedding spores all through the winter after the sterile fronds are long dead. In some cases, the fronds are part sterile and part fertile. The Rattlesnake Fern is an example of this. The fertile portion can be seen rising above the low-lying sterile parts.
These variations provide a means of separating the different species so that they can be identified. It is challenging but The Ferns of Grey and Bruce explains this fully and the illustrations, frond silhouettes and colour pictures facilitate this. There are only 50 species! Hunting for ferns will lead you into a variety of interesting habitats and give you a different view of the natural world.
Author: Owen Sound Field Naturalists
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