Woody plants of characteristics appearance yet of widely variable form, most of them trees of diverse dimensions, some of them erect shrubs, others climbers, all with woody rather than herbaceous stems, usually not branched, and stiff persistent leaves mostly forming a crown at top of plant. Genera upward of 140 and species several thousand, many of which are yet imperfectly understood. Inhabitants of tropics around the world, extending into warm-temperate regions. Many kinds are planted in the warmer parts of the United States, but the botany of them is obscure. (Bailey 163).