Within Apocynaceae, interactions with pollinators are highly structured both phylogenetically and biogeographically. Variation in transition rates between pollination systems suggest constraints on their evolution, whereas regional differences point to environmental effects such as filtering of certain pollinators from habitats. This is the most extensive analysis of its type so far attempted and gives important insights into the diversity and evolution of pollination systems in large clades.

Although Ceropegia species are well known for their complex pitfall flowers that temporarily imprison their pollinators, various aspects of their pollination ecology are still unknown. This study investigated flowering phenology, functional floral traits, and insect visitation in a natural population of a rare endemic lithophyte, Ceropegia thaithongiae Kidyoo. Flowering of C. thaithongiae was not synchronous but staggered. Anthesis lasted mostly 1–2 days, but its duration was shorter in flowers with a pollinium inserted into the stigmatic chamber. Several different insects visited flowers, but only chloropid and milichiid flies were effective pollinators. At anthesis, the epithelial osmophores on the corolla lobes emitted a floral scent that was simple in composition. Nectar of high viscosity was exuded from the nectaries hidden behind the guide rails. When transported by an insect, the pollinarium was attached to bristles on the mouthparts. Size and shape of the thin pellucid margin of the pollinium enable it to fit into the stigmatic chamber in a lock-and-key arrangement. The pollen transfer efficiency was 6.8%. The plant’s staggered flowering and pollination-induced ending of anthesis are advantageous in decreasing competition for pollinators when flower-visiting insects are scarce.

In the insect-pollinated dioecious rattan Calamus castaneus Griff., nectar and pollen rewards, together with visual and olfactory cues, attract insects to male flowers. Pistillate flowers are apparently rewardless. Here, we aimed to clarify the mechanisms assuring visitation and pollination of female flowers. We studied features of flowering phenology and floral biology that affect pollination success of plants of both sexes. The results show that C. castaneus features a striking system of mimicry, quite different from those studied previously in other dioecious plants. The population of C. castaneus was not significantly male biased and no intersexual difference in number of inflorescences per plant was detected. However, male plants began their blossoming earlier and flowered longer than female plants. There was thus an excess of male floral display. This excess should increase the frequency of insect-mediated transport of pollen from male to female plants. Furthermore, on female plants each pistillate flower is accompanied by a sterile staminate flower that appears to contribute to insect attraction. Quite similar in morphology and function to fertile staminate flowers, they produce similar visual and olfactory cues, but less rewards (nectar but no pollen). C. castaneus thus ensures pollination success by intersexual phenological differences and by floral mimicry.Résumé : Chez le rotin (Calamus castaneus Griff.) une espèce dioïque pollinisée par les insectes, les compensations sous forme de nectar et de pollen ainsi que des signes visuels et olfactifs attirent les insectes vers les fleurs mâles. Les fleurs pistillées n'offrent apparemment aucune compensation. Les auteurs ont cherché à clarifier les mécanismes assurant la visite et la pollinisation des fleurs femelles. Ils ont étudié les caractères de la phénologie et de la biologie florale affectant le succès de la pollinisation, chez les plantes des deux sexes. Les résultats montrent que le C. castaneus affiche un système de mimé-tisme frappant, assez différent de ceux étudiés auparavant chez d'autres plantes dioïques. La population du C. castaneus n'est pas significativement biaisée du côté mâle et on n'observe pas de différences intersexuelles dans le nombre d'inflorescences par plante. Cependant, les plants mâles commencent à fleurir plus tôt et fleurissent plus longtemps que les fleurs femelles. Il y a donc un excédent de présentation des fleurs mâles. Cet excès devrait augmenter la fréquence du transport du pollen des plantes mâles vers les plantes femelles via les insectes. De plus, chez les plantes femelles, chaque fleur pistillée s'accompagne d'une fleur staminée stérile semblant contribuer à l'attraction des insectes. Assez semblables morphologiquement et physiologiquement aux fleurs staminées, elles portent des signes visuels et olfactifs similaires, mais moins de compensations (nectar, mais pas de pollen). Le C. castaneus assure ainsi le succès de sa pollinisation par des différences sexuelles phénologiques et un mimétisme floral.

The identity of Ceropegia hirsuta in Thailand has been questioned. Although this plant is quite similar to the original C. hirsuta from India, being entirely hirsute, with yellowishshaded flowers, a curved, funnel-shaped corolla tube, and broad corolla lobes shorter than the corolla tube, there are several clear differences in morphological traits between the materials collected in Thailand and the type and further specimens collected in India. Moreover, C. hirsuta s.s. is restricted to Peninsular India. In this study, using molecular phylogenetic analysis based on DNA sequence data for ITS (nuclear) and trnT-L, trnL, and trnL-F (all cpDNA) markers, and classical morphology-based delineation, we demonstrate that the plant from Thailand represents a species on its own clearly separated from C. hirsuta s.s. as well as from all other known congeners. Therefore, we here describe it as a new species, C. citrina.A detailed description, illustrations, and photographs are provided, together with a comparison of morphological traits of C. citrina, C. hirsuta and another Thai species, C. foetidiflora. We also provide characterization of floral volatile compounds and pollinators.Our study emphasizes that morphological convergence may lead to errors in taxonomic treatment within the genus Ceropegia, and that phylogenetic relationships are largely congruent with geographic distribution.

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