Native plants are those that have grown in a particular location without human intervention. Under the right conditions, they would grown naturally in the same place that they first evolved. They can be planted in their indigenous area with little maintenance.
Native plants can be defined by a large area or a very particular one. For example, plants can be native to the United States or more particularly can be native to Northeast Pennsylvania. The great variety in climates around a country like the United States makes is most convenient for home gardeners to classify them by small regions. For convenience sake, lists of native plants usually are ordered by the state they occur in.
The appeal of native plants is that they are extremely low maintenance. Since they have naturally adapted to soil conditions in a given area, they can grow easily without expensive soils and fertilizers. They are very hardy and can generally grow even in soil considered poor for other breeds of plants. The natural rain fall of the area is usually enough to support the plant, aside from extreme drought conditions, so extra watering is usually unnecessary.
Beginning home gardeners tend to gravitate towards plants that they find visually appealing without considering the maintenance required for them. Exotic plants are those that are not native to an area. They can be quite difficult to grow and often need water, fertilizer and lots of attention to grow well in a non-native area.
Some exotics are invasive, meaning that they will take over an area that they are planted in with rapid and prolific growth. Sometimes this is helpful like when they are used to recolonize swamp lands and help with hurricane control in the southern region of the United States. In a backyard garden, invasive plants can be a bit more bothersome. English Ivy is often planted to grow up a backyard tree because people think it looks pretty. The adverse effect is that the ivy can block sunlight form the tree and stifle it, leading to its eventual demise if gone unchecked.
The best source to purchase native plants is a local nursery or grower. Seeds are a bit more difficult to come by, but some local growers may offer them for a price. Local nurseries are more likely to specialize in those plants suited to a particular climate than a large national chain store would be.