four species of carnivorous bladderworts (Utricularia), and saprophytic species like burmannia (Burmannia biflora) and nodding-nixie (Apteria aphylla). Some baygalls and hanging bogs are no more than a small pool, while others can be a mile across. One author states that the Jack Gore Baygall Unit of the BTNP, at 12 square miles, is the largest baygall in the world. Flats (aka: palmetto-oak flats; wet forests; palmetto-hardwood flats): Dense stands of dwarf palmettos (Sabal minor) are an indicator of this ecosystem and it can have an exotic and tropical look with epiphytes draping from the trees, like Spanish moss (Tillandsia usneoides) and resurrection fern (Pleopeltis polypodioides). Some of the most extensive and well preserved palmetto-oak flats are found around Pine Island Bayou and Little Pine Island Bayou, the area known as the "Traditional Thicket" or "Hunter's Thicket". Flats, often several miles wide, are old river channels and floodplains and their associated bars and levees, filled with centuries of sediments and alluvium deposits. They are some of the flattest and lowest areas in the Big Thicket. Flats are typically poorly drained areas with very deep calcareous soils of a high clay content having vertisols properties, meaning the soil moves, shrinking and swelling with moisture content. Palmetto-oak flats alternate between flooded and dry conditions, with a few inches of water standing for days, weeks, even months after rains, to dry periods in which the soils dry, leaving large and deep cracks in the hard baked surface. The canopy is made up of several hardwoods species of which the swamp chestnut oak or basket oak (Quercus michauxii), laurel oak (Quercus laurifolia), overcup oak (Quercus lyrata), swamp post oak (Quercus similis), and cedar elm (Ulmus crassifolia) are dominant species. Other trees and shrubs filling in the canopy and understory include sweetgum (Liquidambar styraciflua), Carolina ash (Fraxinus caroliniana), blueberry hawthorn (Crataegus brachiacanthua), and arrowwood viburnum (Viburnum dentatum). The shade of the canopy and the severity of the wet and dry conditions limit the species that grow in the understory. However the dwarf palmetto (Sabal minor) thrives, typically growing to about , although occasional specimens can be found up to tall. Some regard the larger specimens as a different species or variety, the Louisiana palmetto (Sabal louisiana), others do not recognize it a valid species. Other understory species found on the flats are creeping spot-flower (Spilanthes americana), Missouri ironweed (Vernonia missurica), lance-leaved water-willow (Justicia lanceolata), and inland