The extensive hardwood forests and forest edges create excellent habitat for many different species of fern and fern-like plants. They differ from flowering plants in that they produce dust-like spores that are the "seeds" by which ferns are propagated. The spores come from sporangia grouped under the fronds on ferns. Ferns drop millions to billions of spores during their lifetime, but few of these find a spot suitable for growth. Ferns are one of the oldest plant forms and have been around for more than 300 million years. The ferns ruled the plant kingdom during the Carboniferous Period (the age of ferns) as the dominant vegetation of that time period. Ferns and their allies can be divided into four classes and the Lakeshore has representatives of three of these classes including the equisetums or horsetails; the clubmosses; and 25 species of the true ferns.