Slippery flowers as a mechanism of defence against nectar-thieving ants.

BACKGROUND AND AIMS: The great diversity of floral characteristics among animal-pollinated plants is commonly understood to be the result of coevolutionary interactions between plants and pollinators. Floral antagonists, such as nectar thieves, also have the potential to exert an influence upon the selection of floral characteristics, but adaptation against floral antagonists has attracted comparatively little attention. We found that the corollas of hornet-pollinated Codonopsis lanceolata (Campanulaceae) and the tepals of bee-pollinated Fritillaria koidzumiana (Liliaceae) are slippery to nectar-thieving ants living in the plant's habitat; because the flowers of both species have exposed nectaries, slippery perianths may function as a defence against nectar-thieving ants. METHODS: We conducted a behavioural experiment and observed perianth surface microstructure by scanning electron microscopy to investigate the mechanism of slipperiness. Field experiments were conducted to test whether slippery perianths prevent floral entry by ants, and whether ant presence inside flowers affects pollination. KEY RESULTS: Scanning electron microscopy observations indicated that the slippery surfaces were coated with epicuticular wax crystals. The perianths lost their slipperiness when wiped with hexane. Artificial bridging of the slippery surfaces using non-slippery materials allowed ants to enter flowers more frequently. Experimental introduction of live ants to the Codonopsis flowers evicted hornet pollinators and shortened the duration of pollinator visits. However, no statistical differences were found in the fruit or seed sets of flowers with and without ants. CONCLUSIONS: Slippery perianths, most probably based on epicuticular wax crystals, prevent floral entry by ants that negatively affect pollinator behaviour. Experimental evidence of floral defence based on slippery surfaces is rare, but such a mode of defence may be widespread amongst flowering plants.

Floral structure and development in Nartheciaceae (Dioscoreales), with special reference to ovary position and septal nectaries.

We present a comparative study of the floral structure and development of Nartheciaceae, a small dioscorealean family consisting of five genera (Aletris, Lophiola, Metanarthecium, Narthecium, and Nietneria). A noticeable diversity existed in nine floral characters. Analyses of their respective character states in the light of a phylogenetic context revealed that the flowers of Nartheciaceae, whose plesiomorphies occur in Aletris and Metanarthecium, have evolved toward in all or part of Lophiola, Narthecium, and Nietneria: (1) loss of a perianth tube; (2) stamen insertion at the perianth base; (3) congenital carpel fusion; (4) loss of the septal nectaries; (5) unilocular style; (6) unfused lateral carpellary margins in the style; (7) flower with the median outer tepal on the abaxial side; (8) flower with moniliform hairs; and (9) flower with weak monosymmetry. We further found that, as the flowers developed, the ovary shifted its position from inferior to superior. As a whole, their structure changes suggest that the Nartheciaceae flowers have evolved in close association with pollination and seed dispersal. By considering inferior ovaries and the presence of septal nectaries as plesiomorphies of Nartheciaceae, we discussed evolution of the ovary position and septal nectaries in all the monocots.

Endosperm development in the Araceae (Alismatales) and evolution of developmental modes in monocots.

The Araceae, a basal-most family of Alismatales that basally diverged subsequent to Acorales in monocot phylogeny, are known to have diverse modes of endosperm development: nuclear, helobial, and cellular. However, the occurrence of nuclear and helobial endosperm development has long been debated. Here, we report a (re-)investigation of endosperm development in Lysichiton, Orontium, and Symplocarpus of the Orontioideae (a basal Araceae), in which nuclear endosperm development was recorded more than 100 years ago. The results show that all three genera exhibit a cellular, rather than nuclear, endosperm development and suggest that the helobial endosperm development reported as an "unmistakable record" from Ariopsis is likely cellular. Thus the Araceae are very likely characterized by cellular endosperm development alone. An extensive comparison with other monocots in light of phylogenetic relationships demonstrates that a plesiomorphic cellular endosperm development is restricted to the three basal monocot orders Acorales, Alismatales, and Petrosaviales, in which evolutionary changes from cellular to nuclear endosperm development occurred twice as major events, once within Alismatales and once as a synapomorphy of the eight remaining monocot orders, including Dioscoreales, Liliales, Asparagales, and Poales, and that helobial endosperm development, which is known for many monocot families, evolved as homoplasy throughout the monocots.