The utility of pollination syndromes in predicting pollinators has been controversial. Flowers of Guihaiothamnus acaulis are tubular and vivid in color, indicating that butterflies might be the dominant pollinators of this species, based on the theory of pollination syndromes. To test this prediction, observations on the floral biology, pollinator behaviors, and breeding system were carried out in two wild populations. The results showed that diurnal and protandrous flowers of G. acaulis could last 7-10 days, and this species was self-incompatible. Thus, the fruit set was pollinator-dependent. In addition, pollen-consuming hoverflies and halictid bees were identified as the major pollinators of G. acaulis; butterflies were recorded as visiting the flower only once. The expanded corolla throat, massive pollen per flower, and high floral longevity suggest that G. acaulis had experienced the process of pollinator shift. Our results indicated that the actual pollinating fauna of plants were determined by complex factors including floral syndromes, the availability of pollinators, and historical adaptation to habitat. Pollination syndromes should be used carefully to predict pollinators of a particular flowering plant species.
Pollen morphology of 27 species, eight subspecies and one variety of Wendlandia was studied using scanning electron microscopy (SEM). Wendlandia pollen are monads, radiosymmetric, small in size, tricolporate (rarely tetracolporate or bicolporate) and spheroidal (rarely subprolate or suboblate) in equatorial view. The compound aperture consists of ectocolpus, mesoporus and endocolpus. In addition, reticulate sexine and granular nexine were observed. The pollen wall ultrastructure of two Wendlandia spp. was examined by transmission electron microscopy (TEM). The exine consists of the tectum, columellae, foot layer and endexine. The endexine is thickened into a costa around the aperture. The intine forms a protruding oncus at the aperture. The palynological characters show a remarkable uniformity among the Wendlandia spp. Differences with Rondeletia, the main genus of tribe Rondeletieae, exist in the exine pattern, the endoaperture and the pollen wall structure. Our observations indicated that the endoaperture type and the structure of the pollen wall of Wendlandia were similar to those of the Gardenieae-Pavetteae-Coffeeae-Octotropideae clade, which provided palynological evidence for a closer relationship of Wendlandia to subfamily Ixoroideae and the transfer of Wendlandia out of Rondeletieae.
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