Some of the oldest extant angiosperm species display floral characteristics that have biologists confused. These plants produce red flowers that bloom early in the spring and exude musky, unpleasant odors. In contrast, most co-blooming spring perennials have light-colored flowers with sweet odors. What is more surprising is that these unusual red-flowered relict species might be exhibiting a form of specialization. By studying these flowers, we hope to determine whether they demonstrate a novel pollination syndrome, of if their unusual combination of floral characteristics evolved to attract a general group of insects. From here, potential inferences may be allowed about the origins of angiosperm-pollinator mutualisms.
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Three of the ancient red-flowered species in our study can be found growing in the Georgia Southern Botanical Garden.
Florida anise (Illicium floridanum) is an evergreen shrub that grows in the understory of wooded ravines from the Florida panhandle up through Louisiana. Fossil records give evidence for the long history of this species, which has existed for some 40+ million years, and was once far more abundant throughout Asia and North America. While the leaves of I. floridanum smell strongly of anise, its deep red flowers, which bloom in early spring, emit odors akin to fish. Very little is known about the pollination of this ancient species.
Calycanthus floridus is a woody evergreen shrub native to eastern North America. It ranges from Florida north to New York, where it thrives in the understory of moist forests. Similar to the genus, Illicium, the leaves of this plant smell strongly medicinal, and for this reason, C. floridus is commonly referred to as sweet shrub or Carolina allspice.
Asimina triloba, the common paw paw, represents the northernmost range of a group of tropical angiosperms (Annonaceae). This species grows as an understory shrub from Illinois to New York, south to Florida and west to Texas. Its flowers bloom in early spring and produce a large, edible fruit which ripens in the fall and is known for its custard-like texture. Each of the red-flowered species that we study has relatives in the same genus which bear white, sweet smelling flowers and tend to bloom in the late spring. We use these white-flowered species for comparison, with the hypothesis that there is a functional significance for the difference in color, odor, and phenology between white and red-flowered species. Based on our understanding of pollinator preferences for floral color and odor, we expect these red flowers to attract different insect pollinators than their white-flowered relatives. If true, the evolution of these floral patterns may be a mechanism for carving a functional niche in the pollination scheme.
From top, Illicium floridanum and its white-flowered relative, Illicium anisatum, can both be found at the Georgia Southern Botanical Garden. Also look for Calycanthus floridus and its white-flowered counterpart, Sinocalycanthus chinensis (middle row). Lastly, the red-flowered Asimina triloba can be found among the specimen at the G.S. Botanical Garden, but the white-flowered Asimina reticulata is restricted to regions of central and southern Florida.
