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Gyrocheilos is a small genus of Gesneriaceae endemic to hight altitude mountains in Southwest China and Guangdong Province, with only five species. This genus is characterized by laterally bending style, which curves 90° at the top of the style and the stigma right at the mouth of floral tube. This unusual floral trait may have special evolutionary and adaptive mechanisms. In this paper, three Gyrocheilos species, i.e. G. chorisepalus, G. retrotrichus, G. microtrichus were examined to figure out the developmental patterns of floral lateral bending. Breeding systems, floral syndrome and pollination processes were also studied in G. retrotrichus at Dawuling Mountain, Guangdong Province, to explore its pollination adaptations. The results were as follows: (1) G. microtrichus had only left-bending style, while right-bending style were observed in several flowers (2%-3% of the total flowers) of G. chorisepalus and G. retrotrichus, although the individuals and populations were dominated by left-bending style. (2) Pollination observation found that style lateral bending occurred at the early stage of floral bud in G. retrotrichus, with two fertile stamens were anther-united and hidden at the middle of the floral throat, and there was no left and right mirror symmetry relationship with the lateral style. (3) The pollen-ovule ratio（P/O）was (456.98±15.55), belonging to facultative outcross breeding system. G. retrotrichus had a certain pollen limitation and self-pollination, but the germination rate of outcross seeds was higher, and there might be inbreeding decline. (4) There were few floral visitors and the frequency was low of G. retrotrichus. The main floral visitors were Halictidae, Bombus and Syrphidae. Bombus were large, and they landed on the bent style and the lower lip of the petals when visiting flowers. The side and lower part of the chest could effectively contact the stigma. (5) The detected reflected lights of flowers were composed of purple and blue-purple lights and the lower lips and outer floral tube with the highest reflection intensity, more likely to attract bees to land on the corolla's lower lip. Molecular phylogeny indicated that the closest genus of Gyrocheilos was Didymorcarpus, which was characterized by style downward bending and mirror-image flowers, suggesting the style lateral bending in Gyrocheilos probably evolved from either of these conditions. In conclusion, the lateral bending style might provide landing platform for pollinators and the stigma above the lower lips increase contact probability the floral visitors, which is an adaptation to the very low insect visitation due to fragmented and foggy habitats in high altitude areas.

Gyrocheilos is a small genus of Gesneriaceae endemic to hight altitude mountains in Southwest China and Guangdong Province, with only five species. This genus is characterized by laterally bending style, which curves 90° at the top of the style and the stigma right at the mouth of floral tube. This unusual floral trait may have special evolutionary and adaptive mechanisms. In this paper, three Gyrocheilos species, i.e. G. chorisepalus, G. retrotrichus, G. microtrichus were examined to figure out the developmental patterns of floral lateral bending. Breeding systems, floral syndrome and pollination processes were also studied in G. retrotrichus at Dawuling Mountain, Guangdong Province, to explore its pollination adaptations. The results were as follows: (1) G. microtrichus had only left-bending style, while right-bending style were observed in several flowers (2% -3% of the total flowers) of G. chorisepalus and G. retrotrichus, although the individuals and populations were dominated by left-bending style. (2) Pollination observation found that style lateral bending occurred at the early stage of floral bud in G. retrotrichus, with two fertile stamens were anther-united and hidden at the middle of the floral throat, and there was no left and right mirror symmetry relationship with the lateral style. (3) The pollen-ovule ratio (P/O) was (456.98 ± 15.55), belonging to facultative outcross breeding system. G. retrotrichus had a certain pollen limitation and self-pollination, but the germination rate of outcross seeds was higher, and there might be inbreeding decline. (4) There were few floral visitors and the frequency was low of G. retrotrichus. The main floral visitors were Halictidae, Bombus and Syrphidae. Bombus were large, and they landed on the bent style and the lower lip of the petals when visiting flowers. The side and lower part of the chest could effectively contact the stigma. (5) The detected reflected lights of flowers were composed of purple and blue-purple lights and the lower lips and outer floral tube with the highest reflection intensity, more likely to attract bees to land on the corolla's lower lip. Molecular phylogeny indicated that the closest genus of Gyrocheilos was Didymorcarpus, which was characterized by style downward bending and mirror-image flowers, suggesting the style lateral bending in Gyrocheilos probably evolved from either of these conditions. In conclusion, the lateral bending style might provide landing platform for pollinators and the stigma above the lower lips increase contact probability the floral visitors, which is an adaptation to the very low insect visitation due to fragmented and foggy habitats in high altitude areas. [ABSTRACT FROM AUTHOR]

Enantiostyly is a floral polymorphism consisting in the presence of two floral morphs that differ in the deflection of the style to the right or left in the populations. Monomorphic enantiostyly consists in plants showing both morphs within an individual and is thought to promote pollen transference between morphs, reduce levels of self-pollination and geitonogamy and avoid damage to floral parts during pollinator’s visit. In this study, we examined the function of this floral polymorphism in a group of plants with non-typical enantiostylous characteristics, the family Vochysiaceae. In particular, we evaluated how floral morphology (both sexual organ separation and the match between complementary sexual organs in the morphs) is related to pollen deposition on the pollinators’ body and to patterns of pollen flow among individuals. For this, we used floral morphometrics, insect captures and fluorescent powder dyes. We confirmed that monomorphic enantiostyly increased pollen transference between morphs compared to non-enantiostyly. Moreover, pollen flow occurred only between flowers of opposite morph. We also observed that pollen deposition on the insect’s body depended on their body shape rather than floral morphology. In fact, an intertegular distance slightly larger than the anther–stigma distance in the flowers increased pollen transference because anthers filaments and stigmas are flexible, which facilitated pollen brushing on insects’ body when approaching the flowers. Since the species are self-incompatible, we further discuss the role of mirror flowers in the reduction of geitonogamy and inbreeding depression. [ABSTRACT FROM AUTHOR]

Gesneriaceae is a pantropical family with diverse floral traits and forms a diversification and endemism center in Southwest China. Mirror-image flowers, a highly specialized pollination system, were discussed in Gesneriaceae with an emphasis on its diversity, systematic distribution, and evolution. Mirror-image flowers was found in seven genera in the subfamily Didymocarpoideae, among which three genera have reciprocal mirror-image flowers(Rhabdothamnopsis, Henckelia, Didymocarpus)and other three genera possess nonreciprocal mirror-image flowers(Paraboea, Ornithoboea, Saintpaulia). Subg. Streptocarpella Engler of Streptocarpus contains both reciprocal and nonreciprocal mirror-image flowers. Gesneriaceae was dominated by nonreciprocal mirror-image flowers with united anthers and hidden sexual organs in floral tubes, distinctive from the typical mirror-image flowers in other families. The main pollinators to mirror-image flowers in these species are small-bodied bees such as Amegilla spp. These unusual floral traits suggest the mirror-image flowers in Gesneriaceae probably had experienced distinctive evolutionary history. Phylogenetic relationships indicate that mirror-image flowers are restricted to the subfamily Didymocarpoideae, which is endemic to the Old World. According to molecular phylogenetic studies, at least five independent origins of mirror-image flowers were found. The highly-specialized pollination mechanism associated with mirror-image flowers might facilitate pollination accuracy and consequently accelerate speciation rate of Didymocarpoideae. It is suggested that molecular phylogenetic methods can be used to explore the evolutionary relationship of reciprocal and nonreciprocal mirror-image flowers in Gesneriaceae to determine the possible role of evolutionary transitions of these two types of mirror-image flowers in the family's speciation histories and long-distance dispersal. [ABSTRACT FROM AUTHOR]

• Background and Aims Gesneriaceae is a pantropical plant family with over 3000 species. A great variety of pollination mechanisms have been reported for the neotropical members of the family, but the details of buzz-pollination and enantiostyly for the family have not been described. We investigated the floral biology and pollination ecology of Paraboea rufescens in Xishuangbanna, south-west China, considering three aspects: (1) the type of enantiostyly exhibited; (2) whether the species is self-compatible; and (3) whether pollinator behaviour could enhance the precision of pollen transfer between flowers of contrasting stylar orientation.• Methods Flowering phenology was monitored once a month during vegetative growth, and once a week during flowering both in the field and under cultivation. Pollination manipulations and pollinator observation in the field were conducted.• Key Results Anthesis occurred early during the morning, and flowers remained open for 1–5 d, depending on weather conditions. Controlled pollinations revealed that P. rufescens is self-compatible, and exhibited inbreeding depression in seed set. Plants were pollinator limited in natural populations. The similar stylar deflection among flowers within a plant limits autonomous self-pollination as well as pollination between flowers. Two species of bumble bees (Bombus spp.), Amegila malaccensis and Nomia sp. effectively pollinated P. rufescens. These pollinators visited flowers in search of pollen with almost the same frequency. None of the pollinators appeared to discriminate between left- or right-handed flowers.• ConclusionsParaboea rufescens exhibits monomorphic enantiostylous flowers and a buzz-pollination syndrome. Floral morphology in P. rufescens and pollinator foraging behaviour seems likely to reduce self-pollination and pollinations between flowers of the same stylar deflection. [ABSTRACT FROM AUTHOR]

Enantiostyly is a floral polymorphism in which two floral forms in the same species differ in deflection of the stigma to right or left position. In monomorphic enantiostylous plants, flowers of the two morphs occur within the same individual, usually in the same proportion. In self-compatible species the function of monomorphic enantiostyly is proposed to increase outcrossing rates and offer a reproductive advantage under pollination limitation. Enantiostylous species are usually self-compatible and show heteranthery, with poricide anthers and pollen as pollinator reward; however, there are families, such as Vochysiaceae, that have different characteristics. We analysed the reproductive system and pollination biology of Qualea parviflora and Q. multiflora, two enantiostylous species from the Brazilian Cerrado that have specific morphological and physiological traits. For this, we characterized flower traits, performed hand pollinations and studied floral visitors. We found no differences between morphs in the proportion of flowers, nectar produced or its concentration, pollen quantity and fruit set. Both species were self-incompatible and quite generalist regarding floral visitors. Enantiostyly in self-incompatible plants seems to confer a reproductive advantage by reducing self-interference resulting from stigma clogging. This novel result helps to expand our knowledge on this complex floral polymorphism and opens new avenues for future research on this topic., (© 2020 German Society for Plant Sciences and The Royal Botanical Society of the Netherlands.)