In Indiana there are no clearly defined floral and faunal zones, as the climate is nearly uniform throughout the entire region, and there is no passage from mountain to lowland or from seacoast to interior. Hence, with certain exceptions, the indigenous plant and animal species are distributed fairly generally throughout the State.
The principal regions in Indiana that can be differentiated according to their characteristic plant life are the Ohio River area in the south, the northern lake and marsh region, and the dunes near Lake Michigan. Most of the plants growing in these regions can be found elsewhere in Indiana, and even in the whole north central area of the United States; but a few plants are restricted to each of these limited sections.
Only in the southern counties along the Ohio is the persimmon common; the black gum tree and the southern cypress are seldom found far north of the Ohio. Certain oaks and shrubs are likewise limited to the southern part of the State.
Many know of the northern Indiana swamps (now cleared and drained) largely through Gene Stratton Porter's novels about the great 'Limberlost.' Outstanding among the trees characteristic of marshy regions are the tamarack and the bog willow. The rarest and most exotic residents of the swamps and dune country are two carnivorous plants: the pitcher plant and the round-leafed sundew. The former has a deep-purple blossom and cylindrical leaves, or 'pitchers,' holding water, into which unwary insects are lured and absorbed. The roundleafed sundew exudes onto its leaves a sticky fluid by which its insect prey is caught and held until the leaves fold over slowly and digestion begins. Floating pondweeds, bladderwort, and water milfoil are common water plants in the swampy regions. Before the marshes were drained, crops of cranberries and blueberries were raised in this region, and peppermint is still gathered for its oil.
In the dune region, shifting hills of sand skirt Lake Michigan for miles and merge gradually into rolling prairies and marshes to the south, a juxtaposition of desertland and jungle that fosters a startling variety of plant life. Great white pines and many species of oaks thrive here; the arctic lichen moss and the jack pine, that sturdy tree of the far north, grow near the sassafras, tulip, sour gum, and pawpaw, natives of the semitropics. The same contrast is apparent everywhere. The pricklypear cactus thrives on the sand wastes, bearing beautiful yellow blossoms; within walking distance bloom irises and orchids in shady moist places. The dune regions contain also the typical trees, shrubs, and flowers that are distributed more generally throughout the State.
In his Trees of Indiana ( 1931), Charles Deam reports 134 species. Of these, 124 are native to Indiana, the remaining ten having been successfully introduced. There are 17 species of oak; the black walnut and many species of maple are common. Especially prominent are the beech, lovingly painted by Indiana artists for its mottled trunk and rich autumn colors; the massive sycamore, gleaming white along the banks of streams; and the majestic tulip tree, or yellow poplar, the State tree. Poplars and hickories of many species are numerous, and there are several common types of fruit trees, notably the apple, cherry, peach, and pear.
Among the ten species successfully introduced are the common catalpa and the golden rain tree. The latter was brought from China by William Maclure and first planted at New Harmony; it is a small, round-topped tree producing large panicles of yellow flowers in June.