Visual signals attractive to friends may also attract enemies. The bright colors of anthers and pollen have generally been thought to attract pollinators. We hypothesize that visual crypsis of anthers, and particularly pollen, should be favored in flowering plants because protection from pollen collectors reduces the loss of male gametes.To understand adaptive strategies relating to the color of pollen, we measured the color of pollen, undehisced anther sacs, and their background, the corolla, with a spectrometer for 104 insect-pollinated flowering species from a natural community in Hengduan Mountains, southwest China.The colors of anthers, pollen and corollas were diverse in these species. The color diversity of exposed pollen was significantly higher than that of concealed pollen (i.e. where anthers are enclosed or shielded by corollas). The color contrast between pollen and corolla was significantly smaller in species with exposed pollen than in those with concealed pollen. Unlike anther color, exposed pollen color tended to match its background corolla color.Our phylogenetic comparative analysis showed contrasting effects of pollen color patterns between flowers with exposed pollen and those with concealed pollen, revealing a strategy of hiding pollen from pollen thieves via visual crypsis.

A great diversity of flower morphology in orchids has long been thought to be selected by diverse pollinators. Habenaria Willd. (Orchidaceae) species are generally characterized by long nectar spurs and pollinated by long‐tongued insects (Lepidoptera), the mechanical fit between the spur and pollinator proboscis length being supposedly caused by “arms race” reciprocal selection. Here, we report that flowers of Habenaria aitchisonii Rchb. f. with nectar spurs (approximately 9 mm) were pollinated by three species of settling noctuid moths whose proboscises varied in length from 10 to 16 mm. When a settling moth crawled on the spikes and probed the flowers for nectar, pollinia were placed on the moths’ legs rather than on other body parts. Our 5‐year survey of pollinia movement and 3‐year supplemental pollination experiments indicated that fruit and seed production in this orchid were not often pollen‐limited at flower level. In a natural population in Shangri‐La, Southwest China, the proportions of pollinia removal and deposition on stigmas by moth legs were 93.8% and 83.5%, respectively. This finding of efficient pollen transfer by the pollinators’ legs in H. aitchisonii adds a new example of diverse pollinia placement on pollinators (here settling moths) in the Orchidaceae.

Nectar, the most common floral reward, is generally used to determine whether an orchid species involves deceptive pollination. Estimates of the deceptive pollination systems with nectarless flowers have ranged from one quarter to one third of the nearly 30 000 species of orchids. These estimates, however, are biased towards temperate-zone, usually terrestrial, orchids. Here we investigated nectar production and property in 34 epiphytic orchid species of the Southeast Asian genus Dendrobium. Twenty-one species were observed producing nectar. The amount and sugar concentration (in bagged flowers) of 12 species varied from 0.45 to 2.78 μL and from 8.1% to 31.1%. The nectar was sucrose-dominant, typical of bee-pollinated flowers. Reconstruction of phylogenetic relationship indicated that transition of nectar secretion occurred in the genus. Spur length was positively correlated with flower size but species with relatively long spurs tended to produce small volume of nectar. Nectar production was strikingly variable among and within individuals in some species, suggesting that a vital measurement of bagged and fresh flowers is needed. Given that the quantitative measurement of nectar or floral reward in orchid species remains scarce, an estimate of deceptive pollination systems awaits further survey in diverse genera.