Ferns (Southern Illinois University Press, 1999), by Robert H. Mohlenbrock, will help readers to gain information about ferns and their growing habits. Gardeners may find useful information for the ferns growing in their area, especially those living in some other Midwestern states. Learn about the climates and soils that draw ferns to specific areas.
Limestone outcroppings are most common along the major water ways in Illinois. As one proceeds south along the Mississippi River, for example, from JoDaviess County to Cairo, one may observe a more or less continuous range of limestone cliffs. These cliffs may come to the water’s edge, or they may be a distance of several miles from the river. The same situation obtains along the Ohio River and, to some extent, along the Illinois River. The ferns which inhabit these limestone cliffs are usually confined to calcareous situations; one species-the walking fern (Asplenium rhizophyllum) -seems equally adapted to sandstone rocks. Pellaea glabella, Asplenium rhizophyllum, and Cystopteris bulbifera may be found on limestone throughout the state; Cryptogramma stelleri is restricted to northern Illinois; Ophioglossum engel mannii, Pellaea atropurpurea, and Asplenium resiliens are only in the southern half of the state. Cheilanthes feei, which is pre dominantly southern, is known also from two northern counties.
Sandstone outcroppings are more abundant in Illinois than are limestone outcroppings. They form the extensive Shawnee Hills, extending across extreme southern Illinois from near the Mississippi River to near the Ohio River; they are conspicuous in north ern Illinois, for example, in LaSalle and Ogle counties. There is generally a distinct fern community on the exposed sandstone rocks or cliffs and on the heavily shaded rocks and cliffs. Only Woodsia obtusa seems equally at home under both extremes of moisture availability.
The sandstone bluff tops regularly sup port the growth of nine species of ferns and fern-allies. Only W oodsia ilvensis is confined to the northern counties, while Woodsia obtusa ranges throughout the state. Lycopodium fla belliforme is known naturally from one northern and one southern county. The remaining six species are confined to the Shawnee Hills of southern Illinois. These are Cheilanthes lanosa, Asplenium pinnatifidum, Asplenium X trudellii, Asplenium X ken tuckiense, Asplenium bradleyi, and Isoetes butleri. This last named species occurs only in moist depressions in the sandstone bluff tops.
Except for the moist woodlands, the shaded sandstone provides the habitat for the most species of ferns and fern-allies in Illinois. Lycopodium dendroideum, Dryopteris X triploidea, and Dryopteris X boottii, each known only from a single station, so far are restricted to northern Illinois; Trichomanes boschianum, Dennstaedtia punctilobula, Polypodium polypodioides var. michauxianum, Asplenium X ebenoides, and Asplenium trichomanes are restricted to southern Illinois. In ad dition, the three species of Osmunda in Illinois, while occupying swampy areas and lowland woods in the northern half of the state, are usually confined to moist sandstone ledges in the ex treme southern counties. The majority of the moist sandstone species may be found in both northern and southern counties. These are Lycopodium porophilum, Lycopodium lucidulum, Polypodium vulgare var. virginianum, Polystichum acrostichoides, Dryopteris carthusiana, Dryopteris intermedia, Dryopteris mar ginalis, Asplenium rhizophyllum, and Woodsia obtusa.
Under this heading are discussed moist, shaded woodlands and open, usually dryish, woodlands. Species listed under the shaded sandstone ferns may be found occasionally in the moist wood lands where they are not associated with rocky outcrops. These species generally are excluded from the discussion in the follow ing paragraph.
The deep ravine, generally underlain by sandstone, provides the habitat for the greatest number of fern and fern-ally species in Illinois. Lush canyons in both the north ern and southern counties are ideal areas for the lover and student of ferns. Most of the moist woodland ferns are wide ranging in Illinois and occur in both northern and southern counties. Common species are Botrychium virginianum, Adian tum pedatum, Polystichum acrostichoides, Onoclea sensibilis, Athyrium pycnocarpon, Athyrium thelypterioides, Athyrium filix femina var. rubellum, Asplenium platyneuron, and Cystopteris fragilis var. protrusa. Wide-ranging species of moist woodlands which are found occasionally are Selaginella apoda, Ophioglos sum vulgatum, the three species of Osmunda, Thelypteris hexa gonoptera, and Cystopteris fragilis var. fragilis. Rare species of moist woodlands which are distributed in both northern and southern counties are Thelypteris phegopteris and Thelypteris noveboracensis.
Only two ferns of moist woodlands are restricted to southern Illinois, and each has been found only a single time. These are Dryopteris X clintoniana and Athyrium filix-femina var. asplen ioides. On the other hand, four ferns or fern-allies are restricted to northern moist woodlands-Equisetum scirpoides, Matteuccia struthiopteris, Gymnocarpium dryopteris, and Dryopteris gal diana.
The open woodlands are generally domi nated by species of oaks and hickories. They usually become rather dry during the summer months. Species regularly found in open woodlands are Botrychium virginianum, Botrychium dis sectum var. dissectum, Botrychium dissectum var. obliquum, Botrychium biternatum (from a single southern county), Botry chium multifidurn ssp. silaifolium (from northern Illinois only), Pteridium aquilinum, and Asplenium platyneuron.
Bogs, Shores, and Standing Water
Most species occupying the aquatic or subaquatic habitats are fern-allies, rather than ferns. The genus Equisetum is the most conspicuous group of aquatic fern-allies. Numerous rivers and many lakes and ponds, both natural and artificial, occur in Illi nois, providing much area for aquatic species. A few unique, rapidly disappearing sphagnum bogs remain in the northeastern corner of the state.
Species found in standing water are few in deed. Five native species and one adventive species ( Marsilea quadrifolia) may be termed true aquatics. The native species are Equisetum fluviatile, Isoetes melanopoda, Isoetes engelmannii (from a single station), Azolla mexicana, and Azolla caroliniana (from a single station).
Shoreline and River Banks
Several species of Equisetum are the chief pteridophytic inhabitants of shores and banks. These species are tolerant of periodic flooding, but live most of their lives out of water. These species are Equisetum variegatum, E. X nelsonii, E. arvense, E. hyemale var. affine, E. laevigatum, and E. X ferrissii.
Species of the northern bogs sometimes occur in great abundance. Two common species are Osmunda cinnamomea and Thelypteris palustris var. pubescens. Species collected rarely from these bogs are Lycopodium inundatum and Woodwardia virginica.
Fields and Railroad Right-of-Ways
Plants which occupy fields and railroad right-of-ways often are adventive species in an area. The few pteridophytes occurring in such situations are native members of our flora, however. Common in fields, particularly along roads, is Pteridium aquilinum. In the gravel embankments of railroad right-of-ways regularly may be found Equisetum arvense and E. hyemale var. affine.
How to Identify a Fern or Fern-Ally
Botanists use written devices known as keys to enable them to identify plants. The keys in this book have been written essen tially in nontechnical language in the hope that more people will find them useful. Where technical terms are introduced in the key, they are accompanied by illustrations.
There are two general keys to enable the user to identify the genus of the fern or fern-ally in question. One of these requires that the specimen has sporangia present; the other is designed for use with sterile (vegetative) specimens. Since sporangia! structures generally are much less variable than vegetative struc tures, the key based on sporangia is somewhat more reliable. It begins first with a key to orders, followed by a key to families, followed by a key to genera. Once the genus is ascertained by using one of the general keys, the reader should turn to that genus and use the key provided to the species of that genus if more than one species occurs in Illinois. Of course, if the genus is recognized at sight, then the general keys should be by-passed. The keys in this work are dichotomous-pairs of contrasting statements. Always begin by reading both members of the first pair of characters. By choosing that statement which best fits the specimen to be identified, the reader will be guided to the next proper pair of statements. Eventually, a name will be derived.