Date of this Version
Prairie Naturalist ((March 1979) 11(1).
Extrafloral nectaries (EFNs) are glands on a plant, not involved in pollination, that produce solutions containing sugars (and other compounds). Long noted by morphologists, EFNs have recently been observed to be part of ant-plant mutualisms. The function of EFNs appears to be to attract aggressive insects, especially ants, which by disturbing or preying upon herbivores, reduce damage to the plant (Janzen, 1966a,b; Elias and Gelband, 1975; Keeler, 1975, 1977; Bentley, 1976, 1977a,b; Schemske, 1978; Tilman, 1978; Inouye and Taylor, 1979; Pickett ad Clark, 1979). Furthermore, they constitute an unusual plant defense against herbivores: at EFNs plants employ ants as a "bodyguard."
Zimmermann (1932), Schnell et al. (1963) and Elias (1979) have analyzed the distribution of EFNs in flowering plant taxa. From their work, it is clear that EFNs are worldwide and represented in varied vascular plants. At least 73 angiosperm families have species which possess EFNs. A few fern species also have EFNs, apparently an advanced character (see Bentley, 1977a). The number of species with EFNs cannot yet be meaningfully estimated, but 907 are known to me.
This paper reports for the first time the proportion and taxonomic distribution of EFN-bearing plants in the flora of a single area. Only from information about distribution of EFN-bearing species will it be possible to identify the selection pressures affecting the geographic and taxonomic presence or absence of EFNs.