Hardiness is the ability of a plant to withstand an area's climate year round. It can refer to the tolerance of low temperatures without protection or to the resistance to drought. For example...

Habitat: Alpine plants that grow in rock crevices have deep, widespread roots in order to take up water and nutrients, and the roots are insulated beneath the rocks. In spring, alpine plants bloom early so that they can disperse seed and become dormant before the cold weather returns. To cultivate these plants, one needs to use free draining soil with little nutrients. The plants also need shelter from high winter rainfall. On the other hand, desert plants are adapted to store water. During the dry season, these plants may lose up to seventy percent of their water content. They may also experience extreme cold. The plants bloom after a rain. To cultivate in a cool, wet climate, one must use a heated greenhouse or grow them as houseplants with little watering.

Climate: In a continental climate, most of the rainfall and heat occurs in the summer while winters are cold and dry. This allows the maturation of woody growth. Cell walls become tough but flexible, allowing the plant to withstand extreme cold. Maritime climates have rainfall occurring year round. There are no temperature extremes because of the large bodies of water nearby. Fluctuation of temperature in the summer prevents the maturation leaving the plants susceptible to cold damage. Excess rain in the winter will cause rot in the roots of dormant plants, and mild weather in the spring causes premature growth that is susceptible to damage from even light frosts.

From "The American Horticulture Society A-Z Encyclopedia of Garden Plants"