Ageratina Spach (1841), in the family Compositae, contains around 290 species, mainly in South America, formerly included in Eupatorium L.. Description Shrubs to 5m or more, or perennials. The leaves are usually opposite, often sweetly scented, leathery, and toothed. The flowerheads are small and white to pinkish-purple, in dense, flat clusters. Phyllaries in 2 or 3 rows, usually narrow. Ray florets usually absent. Stamens 5. Ovary inferior, with 1 cell and 1 ovule; style 1, forked, the branches often long and conspicuous. Pollination is presumed to be by insects, especially butterflies. The fruits are
1-seeded, topped by a pappus of rough bristles. Key Recognition Features The often sweetly scented, sticky leaves and large, flat heads of small, pinkish or white, scented flowers. Evolution and Relationships Ageratina and Bartlettina R. King & H. Robinson were formerly part of Eupatorium L., which is now confined to tall perennials such as the European E. cannabinum L., hemp agrimony, and the American E. purpureum L., the Joe Pye weed. Bartlettina includes some large shrubs from South America, which are similar to Ageratum L.. Ageratina differs from Eupatorium
in having the pappus of 1 row of bristles rather than hairs. Ecology and Geography In scrub; most of the shrubby species are in Mexico and South America, and the North American species are mostly herbaceous. Comment Ageratina ligustrinum (DC) R. King & H. Robinson is often cultivated in mild climates for its aromatic leaves and late flowering; in frosty areas it can be grown as a herbaceous perennial. |
