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A new species, Lasianthus konchurangensis V.S.Dang, T.B.Tran & T.D.Ha (sect. Lasianthus), is described and illustrated from Kon Chu Rang Nature Reserve, Gia Lai Province, the Central Highlands of Vietnam. Lasianthus konchurangensis resembles L. foetidissimus but differs in having larger leaves, more secondary veins, larger calyx and purple corolla. Photographs, vernacular name, preliminary conservation assessment, and a table comparing L. konchurangensis with L. foetidissimus are provided.

Lasianthus kbangensis V.S.Dang, Vuong & Naiki, a new species belonging to Lasianthus sect. Nudiflorae of Rubiaceae from the Central Highlands of Vietnam, is described and illustrated. This new species is similar to L. oblongilobus H. Zhu, but differs in having larger leaves, longer petioles, smaller calyx (calyx lobes) and corolla, and the color of ripen fruits. A table comparing the new species to closely related species is provided.

Two new species, Lasianthus fansipanensis V.S. Dang & Naiki and Lasianthus sapaensis V.S. Dang & Naiki (sect. Nudiflorae), were discovered in the Hoang Lien National Park of northern Vietnam and are here described and illustrated. Colour photographs, preliminary conservation assessment, and tables comparing these two new species against two closely related species are also presented.

Lasianthus honbaensis V.S. Dang, Tagane & H. Toyama sp. nova (Rubiaceae) is described and illustrated from Hon Ba Nature Reserve, Khanh Hoa Province, southern Vietnam. It resembles L. inodorus and L. inodorus subsp. pubescens in leaf morphology, but differs from them in having shorter stipules, calyx tubes and corolla, and orange fruits. It is also similar to L. latifolius and L. calycinus in deeply disected calyx lobes and orange fruits, but differs from them by having persistent bracts and shorter calyx tubes. A table comparing the new species with its closest allies is provided.

Two new species of Lasianthus (Rubiaceae), L. thuyanae V.S. Dang & Naiki from Ba Vi National Park, Ha Noi City, northern Vietnam, and L. tamdaoensis V.S. Dang from Tam Dao National Park, Vinh Phuc Province, northern Vietnam, are described and illustrated. Lasianthus thuyanae is closely related to L. curtisii but differs from it by having larger stipules and corollas, and a differently coloured calyx. Lasianthus tamdaoensis resembles L. filipes and L. longipedunculatus but differs from them by having longer petioles and larger corolla lobes.

A new species, Lasianthus bidoupensis V.S. Dang & Naiki (Rubiaceae) is described and illustrated from Bidoup Nui Ba National Park, Lam Dong Province, southern Vietnam. It resembles L. yaharae which was recently discovered from Mt. Hon Ba and L. dalatensis which is endemic to Dalat, southern Vietnam. However, L. bidoupensis differs from them by having larger leaves and bracts, longer petioles, stipules, calyx and corolla tubes, and deep-red mature fruits.

Heterostyly is a genetically controlled sexual polymorphism promoting outcrossing by animal pollinators. The occurrence of heterostyly in angiosperms was investigated, and 199 genera in 28 families in 15 orders were recognized as taxa that contain heterostylous species. A correlation between the occurrence of heterostyly and ploidy level was found in some limited groups in Primulaceae and Rubiaceae. In such taxa, individuals with a lower ploidy level tended to have heterostyly and individuals with a higher ploidy level tended to have monomorphic flowers. It appears reasonable that the first step of the breakdown of heterostyly was the recombination of the supergene in a diploid heterostylous plant, and then poyploidization incidentally occurred. Polyploidization itself does not necessarily appear to have direct effects on the breakdown of heterostyly.

Somatic chromosomes were observed in 661 individuals of 14 taxa, nine species and five varieties, of Damnacanthus (Rubiaceae). Chromosome numbers are reported for the first time for 13 taxa. Diploid (2n = 22) and tetraploid (2n = 44) counts were obtained. Distyly is reported for the first time for four species, D. angustifolius, D. henryi, D. labordei, and D. officinarum. A strong correlation exists between chromosome number and occurrence of distyly. Regardless of taxa in Damnacanthus, distylous populations are diploid, and monomorphic populations are tetraploid. Flowers of the monomorphic populations observed have a long style and short stamens with few exceptions. Polyploidization may have caused the breakdown of distylous to monomorphic flowers. In D. indicus, leaves from the tetraploid populations tend to be larger than those from the diploid populations. Populations of tetraploid D. indicus were distributed in more northern areas than those of the diploid. Three types of sympatric distribution were found for the varieties of D. indicus in Japan: diploid and tetraploid, two diploids, and two tetraploids. Based on the present chromosome number study, the taxonomy of the varieties of D. indicus should be revised.

Herein, Mussaenda recurvata, a new species from Hon Ba Nature Reserve, southern Vietnam, is described and illustrated. This species is morphologically similar to M. longipetala, distributed from southern China to northern Vietnam, in having recurved stipules and densely pilose and puberulent hairs throughout, but differs in its strongly recurved calyx lobes, a shorter corolla tube, and ovate corolla lobes. The species is morphologically heterostylous and it appears to be functionally dioecious. An updated key to Mussaenda species in Vietnam, Laos, and Cambodia is also provided.

The floral morphology and reproductive ecology of a scandent shrub species, Mussaenda parviflora Miq. (Rubiaceae), were studied on Iriomote and Amami Ohshima Islands, Japan. The morphological study demonstrated that M. parviflora was gynodioecious. Crossing experiments, however, revealed that it was functionally dioecious. The flowers were visited mainly by butterflies in the daytime and mainly by crepuscular hawkmoths in the evening. Dioecy in this species is thought to have evolved from distyly. Dioecy of this species, which is pollinated by long-tongued Lepidoptera, is unusual as the evolution of dioecy from distyly in plants with long corolla tubes is thought to have been triggered by a pollinator shift from long- to short-tongued insects. In this species, however, two floral morphological features may have caused the evolution. The first feature is the presence of many upward-facing hairs covering the inner surface of the upper part of the corolla tube; these hairs appear to have impeded pollen flow from long- to short-styled flowers. The second feature is the overlap in anther height between the two types of flowers, which may have reduced seed set by clogging stigma with incompatible pollen grains. Accordingly, male sterility in long-styled plants may have evolved.

We document distyly in Damnacanthus (Rubiaceae) and investigate pollen morphology in the genus. Within nine taxa in Japan (four species, four varieties and one form), five show distyly. Non-distylous taxa of Damnacanthus always have a long style and short stamens. We examined the pollen morphology of all taxa of Damnacanthus in Japan. The pollen grains of Damnacanthus are 3- to 5-orthocolporate or sometimes loxocolporate. Polymorphic pollen is sometimes observed even within a single flower. Pollen dimorphism is associated with distyly; pollen grains from short-styled (thrum) flowers are significantly larger than those from long-styled (pin) flowers, and the muri are smooth in pin flowers whereas the pollen grains of thrum flowers have minute granules on the top and/or on the sides. In non-distylous taxa, in which the style is longer than stamens, the muri are always provided with minute granules. Interestingly, the pollen grains with granules in the non-distylous taxa contrast with the pollen of the distylous taxa, because granulate pollen grains are found only in thrum flowers. Although Damnacanthus is a stenopalynous genus, the number of colpi is useful for delimiting taxa. Based on palynological characters, we conclude that Damnacanthus should be revised.