We have noted that carnivorous plants occur mainly in acid, freshwater wetlands. As is the case with all generalizations, this one has an exception or two. Drosophyllum luscitanicum, a native of Portugal and parts of Morocco, which will therefore not concern us further in this volume, occurs in semiarid regions. Of concern to us is a pitcher plant, Sarracenia purpurea, which can occasionally be found in alkaline marl bogs of the northeast as well as in its usual home in acid bogs.
Now we are going to make a quick tour of major sections of North America and take an overview of broad areas where categories of carnivorous plants can be found in suitable locations within the various areas.
Fig. 1-3. Sarracenia purpurea, a pitcher plant, with a tubular leaf trap of the pitfall type.
Fig. 1-4. Drosera capillaris, a sundew, with traps of the "flypaper," or adhesive, type. The entire flattened rosette is about 5 cm across. Note the numerous gland hairs with sticky secretions at their tips.
In the eastern two-thirds of Canada and the northeastern quadrant of the United States, carnivorous plants are most often found in the classic acid sphagnum bog with which even the weekend naturalist is likely familiar. A northern sphagnum bog is usually an ancient glacial lake that has matured into a bog by becoming partially filled with undecayed plant detritus. It is then overgrown by large masses of various species of Sphagnum and other mosses, all tending to produce a very acid growing medium. As the bog further matures, or ages, other small plants, followed by larger woody plants, gradually move in toward the center of the former lake until finally a northern forest results. Carnivorous and other bog plants are then crowded out.
But while the bog is relatively young, one can often find the pitcher plant Sarracenia purpurea growing in profusion along with various sundews (Drosera) and some bladderworts (Utricularia), the latter either in the sphagnum or in the open acid water often found in the center of a bog. Many bogs are still basically large lakes or ponds with more open water than sphagnum mat, and in such areas the carnivorous plants grow along the lake margins. In more sandy, open places along the shores of large lakes and the Great Lakes, butterworts (Pinguicula) may be found.
We mentioned briefly the marl bog. This is a special area in which the seepage of spring water over a flat surface causes calcium carbonate to percolate up from limestone deposits. The alkaline marl results in conditions just the opposite from those of the sphagnum bog. But marl bogs do otherwise have some of the features that allow the growth of carnivorous plants, among them diminished nitrogen and other salts, constantly wet conditions, and the absence of many other plants that might become competitors. The presence of the normally acid-loving pitcher plant Sarracenia purpurea in some of these areas indicates another form of adaptation that is not completely understood. A sundew, Drosera linearis, is adapted to marl bogs around the Great Lakes, where it is found almost exclusively. On the other hand, many other carnivorous plants will not colonize marl bogs. One final point on the ecology of the northeastern region is that it has been repeatedly glaciated, and after each ice flow retreated, plants have moved north again to repopulate suitable sites. Thus, plant populations in this region have been stable for relatively short geologic periods.
Progressing a little south, we come to the remarkable New Jersey Pine Barrens, which is a gross misnomer since to the eye of a naturalist they are anything but barren. But the early colonists did not find the broad, sweeping, sandy hills conducive to farming, so they declared them barren, and only timber and mining interests were able to utilize the region to any extent. Here there are many acid bogs along and in old lakes, slow streams, and sluggish springheads. The pitcher plant Sarracenia purpurea is quite abundant, and the kinds of sundews (Drosera) and bladderworts (Utricularia) become much more diverse; but butterworts (Pinguicula) are absent.
In the southern Appalachian Mountain chain from Pennsylvania south to its terminus in Alabama, there are occasional relic bogs that have survived ancient geologic activity that created these mountains from a peneplain (an almost level plain). The bogs are very much like the acid sphagnum type of the far north in general appearance, but they are most often found at a confluence of springheads or beside a stream rather than around the edges of maturing glacial lakes, which are not present in these areas. The kinds of carnivorous plants found in these mountain bogs are limited: the pitcher plant Sarracenia purpurea, a sundew (Drosera), a few bladderworts (Utricularia), and two other pitcher
plants that are unusual cases and will be discussed in Chapter 3. More bogs are found as the mountains recede into the eastern foothills and piedmont sections of the southeastern states, and the diversity of carnivorous plants increases as we approach the coast.
The last general area to consider in the east is the southeastern coastal plain, which runs as a great arc from eastern Virginia south and west to eastern Texas, including all of Florida. This area was suboceanic before the coastal uplift, and it is probable that the rich carnivorous plant life there is ultimately descended from plants of the former peneplain which has now been replaced by mountains and piedmont. The plants apparently migrated down rivers to habitats more similar to their ancestral locations. Since then, further cross migrations and evolution have undoubtedly occurred. The few forms adaptable to mountain climates were able to stay behind and evolve still further, some probably not adapting at all to coastal habitats, and some adapting to both mountains and plain.
The southeastern coastal plain is our richest area for both the number of species and the total population of carnivorous plants; about ninety per cent of the species to be discussed in this book can be found there. Many, such as the Venus' flytrap (Dionaea muscipula), are found there exclusively. While sphagnum bogs of the streamside or springhead type are found in this
Fig. 1-5. A typical Appalachian Mountain bog. Note the background trees and mountaintop. The bog is grassy with a ground layer of sphagnum moss. There is water 2-3 cm deep in most places. This is a confluent spring bog, and the drainage stream is seen in the lower right-hand corner.
Fig. 1-6. A southeastern coastal plain savannah. The trees are lightly scattered among grasses and sedges. Some pitchers of Sarracenia flava can be seen above the grass in the foreground.
region in abundance, the most characteristic habitat is a savannah, or grass-sedge bog. This is a low, flat or slightly sloping, sandy area with high water table and supporting predominant stands of grasses, sedges, and rather widely spaced longleaf pines. A healthy savannah is quite moist and acid.
Traveling rapidly across the continent, there is a paucity of carnivorous plants in the mid-plains and prairie: one species of sundew (Drosera) in wet pockets of the southern plains, and some bladderworts (Utricu-laria) in scattered aquatic sites. The deserts and eastern Rocky Mountains are devoid of carnivorous plants.
Parts of the Pacific mountain slopes are a different matter, particularly from northern California into Oregon. Again there are sphagnum bogs alongside or heading mountain streams, as there are in the eastern mountains. Curiously, there are several of the same kinds of sundew (Drosera) and bladderworts (Utricu-laria) that are found in the east, and a butterwort (Pinguicula) can also be found there. Quite unique is the California pitcher plant, Darlingtonia californica, a member of the same family (Sarraceniaceae) as the eastern pitcher plants but ranked in its own genus.
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