If you live in Europe or North America, you are probably familiar with Campanula (bellflowers) and Lobelia (cardinal flower) and think of these as a group of small herbaceous flowers. However, if you live in Africa or Hawaii, you might think first of the spectacular palm-like tree-Lobelias. Both the small garden flowers and tall trees belong to the Campanulaceae, a family of about 70 genera and 2000 species of asterid flowering plants.
Diversity of Form : Above at left, a population of tiny Downingia from a vernal pool in California. Most species are only a few inches tall, and bloom only along the edges of temporary ponds that form in the spring. At right, Lobelia cardinalis (cardinal flower) blooming on a hillside in Mexico. Though much smaller than their African and Hawaiian cousins, these lobelias have the same basic architecture and flower structure. (Click on either of the pictures above for a larger image).
Despite the wide variety of growth forms, it is possible to recognize members of the bellflower family through several simple characteristics. Firstly, the phloem (food-distributing tissue) contains a system of glands that produce latex, a sticky, milky sap that oozes from the plant when it is damaged. The latex discourages many insects and other animals from nibbling on the stems and leaves. Secondly, the ovary of the flower is inferior, or located below the point at which the petals are attached. This means that insects visiting the flower will not eat or damage the immature seeds. Thirdly, members of the family do not have food reserves of starch, as do most other plants, but store it as inulin, another polysaccharide.
Perhaps the most interesting character is one the Campanulaceae shares with the closely related Asteraceae (sunflower family). Inside the flower, the five stamens are arranged closely together around the central female style and are often fused together, thus forming a little cylinder. When they are mature, the stamens release their pollen into the center of the tube they form, where the pollen collects. The style will then grow longer, slowly pushing the mass of pollen out of the tube, where it then falls on the backs of bees that visit the flower for nectar. Once all the pollen is pushed out and the female style is mature, the tip will split open to reveal sticky surfaces where it can receive pollen from other flowers. In other words, the flower will not pollinate itself, because the pollen is released and pushed out of the way before it is ready to be pollinated. However, there are species that take out insurance on pollination by allowing the sticky tips to eventually coil back into the remnants of pollen in the flower, just in case the bees weren't as busy as they're fabled to be.
Two major subfamilies : The bellflower family is divided into three subgroups, but nearly all the species belong to one of two subfamilies: the Campanuloideae, which have flowers with five similar petals (as seen above at left in the flowers of Githopsis from western North America), and the Lobelioideae, whose flowers have a lower "lip" formed by three enlarged petals (as seen above at right in the flowers of Downingia).
The Campanulaceae grow almost everywhere on Earth except the Sahara, Antarctica, and northern Greenland. Many species are grown in gardens for their large colorful flowers, which are usually red, blue, or purple, but sometimes yellow. The blue color is attractive to bees, though other insects may visit the flowers, and some red-flowered species may be visited by birds or butterflies.
Pretty flowers are not the only potential benefit from this group. Many species produce chemical compounds in wide variety. Some of these compounds are highly toxic, but others have been used to treat asthma and other breathing disorders. Perhaps the best known compound is lobeline, a mild narcotic which provides the slight rush and calming effect of nicotine, but which does not appear to be addictive. As such, it can be used as an aid to quit smoking, though its sale is now regulated in some countries.
The only report of fossil pollen from the Campanulaceae comes from the Pliocene of New Zealand (Mildenhall, 1980), which is rather surprising when one considers the many species and global distribution of the family. In fact, some close relatives of the Campanulaceae have fossils in the Oligocene and earlier. Based on the fossil record of these relatives, the group's ancestors must have evolved before the end of the Cretaceous. Perhaps additional seardhing will locate these elusive fossils.
D. J. Mabberley, 1974. The pachycaul lobelias of Africa and St. Helena. Kew Bulletin 29(3): 535-584.
S. Magallón, P. R. Crane, & P. S. Herendeen, 1999. Phylogenetic pattern, diversity, and diversification of Eudicots. Ann. Missouri Botanical Garden 86(2): 297-372.
D. C. Mildenhall, 1980. New Zealand Late Cretaceous and Cenozoic plant biogeography: a contribution. Palaeogeography, Palaeoclimatology, Palaeoecology 31: 197-233.
Jan Muller, 1981. Fossil pollen records of extant angiosperms. The Botanical Review 47(1):1-142.
Thomas J. Rosatti, 1986. The genera of Sphenocleaceae and Campanulaceae in the southeastern United States. Journal of the Arnold Arboretum 67:1-64.