Caladiums are aroids that grow from a tuber which is a subterranean round to elongated fleshy rhizome which serves as a storage organ.  These tubers are incorrectly called a "bulb". We grow them for their large, colorful, and very showy leaves.  Caladiums have no stems!  Technically they grow on long petioles that rise directly from the tuber. The petioles are attached to the leaves at or near the center, rather than at the end. The leaves have a large variety of shapes, sizes and color mixture variations.  There are literally thousands of selections.  At least one thousand named Caladium cultivars exist, mostly with lance or heart shaped leaves. 

Both hybrids and species prefer damp shaded conditions and few if any will tolerate direct sunlight. The caladium inflorescence (flower) is normally about 9 inches long with a greenish white spadix and spathee (the fleshy upright spike and "bloom").  The majority you today are hybridized forms and are grown in the Tampa Bay region of Florida where there are farms that grow nothing other than caladiums.  

The Missouri Botanical Garden website TROPICOS lists almost 200 known species.  Wild plants grow naturally in tropical South American rain forests and on some Caribbean islands such as Trinidad.   The plants prefer well drained very humus rich soil that is slightly acidic.  Don't add lime to your caladium beds or pots which serves only to raise th pH.  There are also plants in the Xanthosoma family which closely resemble Caladiums and are often difficult for non-scientific types to identify correctly.