Studies on the Reproductive Characteristics of Cimicifuga nanchuanensis (Ranunculaceae), an Endemic Endangered Species to China

Aspects of the reproductive biology of Cimicifuga nanchuanensis Hsiao have been studied to shed light on the endangerment of this species, endemic to Jingfo Mountain in Sichuan Province of China. The only one population of C. nanchuanensis includes 6 000 ~ 8 000 individuals, in which adult blooming plants accoum for 19%. Inflorescence is panicle,flowering period lasts from mid August to early October and fruits ripe in mid or late November. C. nanchuanensis is dichogamous and the stigmas mature 7 days after withering of flower. In natural conditions the rate of seed-setting is 5.8% ~ 7.0% in average. However, hand pollination can raise the rate greatly to 28.0%. Endosperm type is nuclear and embryos are just at the globular stage when seeds shed from their maternal plants. Pollen limitation is one of the reasons for this species endangerment.     

Male and female booths with separate entrances in the tiny flowers of Guazuma ulmifolia (Malvaceae–Byttnerioideae). I. Structural integration

In spite of their tiny dimensions (3×5 mm²), the strongly honey-scented flowers of Guazuma ulmifolia (Malvaceae–Byttnerioideae) provide six sexual chambers. A central female unit is surrounded by five interconnected male compartments. At the onset of anthesis the strap-shaped odoriferous petal appendages form an open star with the female chamber in the centre. Hereafter, they wilt, intermingle and finally lock access to the stigma. Meanwhile, wilting sepals liberate new entrances from the back between the petal claws. They give way to nectar-offering male chambers. In each of them a well-lit (but closed) window lures the visitor into a standard position for passive pollen uptake. Finally, the insects have to back out of one of the rear entrances. It remains unknown how the minute visitors (maximum height ca. 0.5 mm) – if ever – overcome the distance to another Guazuma tree.     

3种雌雄异熟樟科植物开花动态的比较研究

为了解樟科植物雌雄异熟的繁育系统特点,对3种樟科植物阴香(Cinnamomum burmannii)、紫楠(Phoebe sheareri)和浙江楠(Phoebe chekiangensis)雌雄异熟花的开花动态进行了比较研究。结果表明,3种植物雌性功能期的开始时间、雌性功能期和雄性功能期的时间分配有差异。3种植物的主要传粉者均为中华蜜蜂,在雌性功能期和雄性功能期均有访花;在雌性功能期第四轮退化雄蕊蜜腺和雄性功能期第三轮花丝基部的蜜腺分泌花蜜,不同开花阶段的花蜜蜜量和含糖量没有显著差异;柱头可授性和花粉活力在雌性和雄性功能期均较高;雌性功能期和雄性功能期均有自然花粉落置;座果率均是异交补粉自然套袋,表明都存在一定的传粉限制。因此,樟科植物雌、雄性阶段时间分配的不同,可能与退化雄蕊蜜腺和第三轮雄蕊附属蜜腺的分泌节律有关。     

Breeding system and bumblebee drone pollination of an explosively pollen‐releasing plant,Meliosma tenuis (Sabiaceae)

• Explosive pollen release is a mechanism used by some angiosperms that serves to attach pollen to a pollinator's body. It is usually adopted by species with zygomorphic tubular flowers and pollinated by birds and bees. The tree genus Meliosma (Sabiaceae, Proteales) has unique disc‐like flowers that are externally actinomorphic, but internally zygomorphic, and release pollen explosively.
• To elucidate the adaptive significance of explosive pollen release, we observed flowering behaviour, the breeding system and pollinator visits to flowers of the Japanese species Meliosma tenuis in a temperate forest. Flowers bloomed in June and were nectariferous and protandrous. Explosive pollen release was triggered by slight tactile stimuli to anther filaments or staminodes in male‐stage flowers.
• Because pollen cannot come into contact with the pistils enclosed by staminodes, M. tenuis is functionally protandrous. Artificial pollination treatments revealed that M. tenuis is allogamous. The dominant flower visitors were nectar‐seeking drones of the bumblebee species Bombus ardens (Apidae). The drones’ behaviour, pollen attachment on their bodies and fruit set of visit‐restricted flowers suggest that they are the only agent triggering the explosive pollen release mechanism, and are the main pollinator of M. tenuis.
• The finding that bumblebee workers rarely visit these flowers suggests that the explosive pollen release has another function, namely to discourage pollen‐harvesting bumblebee workers.