| Valerianaceae (Asteridae, Dipsacales) contains about 300–350 species that have been traditionally placed in 14–17 genera. Like other Dipsacales, Valerianaceae have opposite leaves, sympetalous corollas, and inferior ovaries and like the related Morinaceae and Dipsacaceae, are basically herbaceous plants. They are further characterized by small, often asymmetric flowers, and a distinctive secondary chemistry, including a variety of valepotriate compounds. Members of this group occur in a wide variety of ecological settings throughout the Northern Hemisphere and the Andes of South America, where they are often found at mid- to high-elevations. Triplostegia and Nardostachys, for example, are found exclusively in the Himalayas. Likewise, several species of Valeriana and Patrina are endemic to the high mountains of Asia and Japan. Throughout their range in South America, the species of Valerianaceae are especially abundant and diverse in the paramo, scattered along the crests of the highest ranges in the northern Andes or on isolated mountaintops from 3000 to 5000 meters. Paramo is divided into several vegetation zones, defined by altitude, the soil types, and the plant growth forms found. The species of Valerianaceae occur in all of these vegetational zones and exhibit a wide range in growth forms, from rosette plants (V. rigida), microphyllous shrubs (V. microphylla), to annual vine-like species (V. chaerophylloides).; Data presented here suggest that, although the Valerianaceae form a well supported clade, the species that occur in South America do not. Species of Plectritis (that occur in North America) appear to be more closely related to the South American valerians than they are to other North American species. Estimates of the timing of the arrival to the South American continent vary greatly depending on the method used. However, all methods suggest that the South American valerians dispersed to South America prior to the formation of the Isthmus of Panama. Regardless of the age of the species, this group still appears to be an example of a group showing tremendous morphological diversity and occupy a wide range of habitats. |
