Pollination ecology of Clerodendrum indicum (Lamiaceae): first report of deceit pollination by anther-mimicking stigma in a bisexual flower

Clerodendrum indicum (Lamiaceae) is a medicinally important shrub. We have studied the details of its pollination ecology which was hitherto unknown. The work was done during three consecutive years 2012-2014, based on 118 plants occurring in three widely separated wild populations in West Bengal, India, together with 25 individuals grown in an experimental plot. Details of flower structure and dynamics of floral events, pollen production and pollen dispersal, visitors and pollinators, floral attractants and floral rewards and pollen transfer mechanism have been worked out by standard methodologies with a 10x high resolution hand lens (IRL), a Leica WILD M3B Stereo-binocular microscope (Switzerland) and a Leica DMLB compound bright field light microscope (Germany). The tubular flower of four-day longevity attracts its visitors by visual cues. Flowers are visited regularly by ten species of insects. On the basis of the visitor behaviour, these can be classified into three distinct categories, viz., visitors belonging to Category-I act on cushion and trichome nectaries of calyx and corolla respectively, those of Category-II act on the dehisced anthers and trichome nectaries of corolla while those of Category-III act on dehisced anthers as well as receptive stigma. Majority of the visitors belong to either Category-I or Category-II. They visit only the 2nd day flowers and never visit a 3rd day flower when the stigma assumes receptivity. Therefore, they are not regarded as pollinators but, act as pollen and/or nectar robbers. Those are discriminated by offering secretions from extra-nuptial nectaries of the flower. Visitor species of Category-III, represented by a species of Trigona, constitute the legitimate pollinator of the plant and thereby, making the plant monophilic. Pollen presentation from the bisexual, dichogamous and protandrous flower takes place on the 2nd day, while the stigma assumes its receptivity on the 3rd day of flower opening. Pollen transfer to the body of the pollinator by a 2nd day flower in its male phase is achieved by offering edible pollen grains. On the other hand, a 3rd day flower at its female phase is devoid of the reward (pollen grain). The yellow shiny receptive stigma of such a flower strikingly mimics the freshly dehisced anthers and the pollinators being lured by such a stigma inadvertently transfer pollen onto it. C. indicum is so far the only known species of flowering plants where deceit pollination occurs by anther-mimicking stigma in a bisexual flower.

Ecología y evolución de la polinización por engaño

In this work we reviewed the biology of deceit pollination from an ecological and evolutionary perspective. Species pollinated by deceit are characterized because a percentage of their flowers do not produce rewards, and therefore these species get the advantages derived from pollinators without paying the costs. In this review, we first described the different types of deceit occurring in nature, as well as the selective pressures involved on its evolution. We then reviewed and discussed the theoretical framework of deceit pollination and the relevant aspects of its main components: frequency-dependent se lection, flower resemblance, and the sensorial capacities of pollinators.

Phylogenetic analysis of Andinia (Pleurothallidinae; Orchidaceae) and a systematic re-circumscription of the genus

Most of the species studied in this paper have previously been placed in either Pleurothallis or Lepanthes. However, at one time or another, members of the group have also been placed in the genera Andinia, Brachycladium, Lueranthos, Masdevalliantha, Neooreophilus, Oreophilus, Penducella, Salpistele and Xenosia. Phylogenetic analyses of nuclear ITS and plastid matK sequences indicate that these species form a strongly supported clade that is only distantly related to Lepanthes and is distinct from Pleurothallis and Salpistele. Since this clade includes the type species of Andinia, A. dielsii, and it has taxonomic precedence over all other generic names belonging to this group, Andinia is re-circumscribed and expanded to include 72 species segregated into five subgenera: Aenigma, Andinia, Brachycladium, Masdevalliantha and Minuscula. The required taxonomic transfers are made herein. We hypothesize that convergent evolution towards a similar pollinator syndrome involving deceit pollination via pseudocopulation by Diptera resulted in a similar floral morphology between species of subgenus Brachycladium and species of Lepanthes; hence the prior placement of the species of subgenus Brachycladium in Lepanthes. Species of the re-circumscribed Andinia are confined exclusively to the Andes, ranging from about 1,200 to 3,800 m, from Colombia south to Bolivia, making the generic name very apt. Elevational distributions of the individual clades are discussed in relation to the possible evolutionary diversification of the most species-rich clade, subgenus Brachycladium.

Orchid phylogenomics and multiple drivers of their extraordinary diversification

Orchids are the most diverse family of angiosperms, with over 25 000 species, more than mammals, birds and reptiles combined. Tests of hypotheses to account for such diversity have been stymied by the lack of a fully resolved broad-scale phylogeny. Here, we provide such a phylogeny, based on 75 chloroplast genes for 39 species representing all orchid subfamilies and 16 of 17 tribes, time-calibrated against 17 angiosperm fossils. A supermatrix analysis places an additional 144 species based on three plastid genes. Orchids appear to have arisen roughly 112 million years ago (Mya); the subfamilies Orchidoideae and Epidendroideae diverged from each other at the end of the Cretaceous; and the eight tribes and three previously unplaced subtribes of the upper epidendroids diverged rapidly from each other between 37.9 and 30.8 Mya. Orchids appear to have undergone one significant acceleration of net species diversification in the orchidoids, and two accelerations and one deceleration in the upper epidendroids. Consistent with theory, such accelerations were correlated with the evolution of pollinia, the epiphytic habit, CAM photosynthesis, tropical distribution (especially in extensive cordilleras), and pollination via Lepidoptera or euglossine bees. Deceit pollination appears to have elevated the number of orchid species by one-half but not via acceleration of the rate of net diversification. The highest rate of net species diversification within the orchids (0.382 sp sp −1 My −1 ) is 6.8 times that at the Asparagales crown.

Pollination of slipper orchids (cypripedioideae): a review

Cypripedioideae (five genera; ca. 176 species) are widespread in temperate and tropical Asia and America. About a quarter (42) of the species have been studied to determine their pollinators and/or breeding systems. All flowers are one-way traps pollinated by insects of particular types and size. Slipper orchids are selfcompatible and pollinated by deceit. Most Cypripedium species are pollinated by bees, whereas some smallerflowered species are pollinated by flies, and a few are pollinated by both. Most bee-pollinated Cypripedium species appear to be generalized food mimics. The fly-pollinated species have evolved diverse pollination systems that utilize a variety of flies as pollen vectors, including fruit flies, dung flies, and a fungal spore-eating hoverfly (Syrphidae). Most species of the tropical Asian Paphiopedilum and tropical American Phragmipedium are pollinated by hoverflies; flowers of many species in both genera have aphid-like spots that attract gravid female hoverflies that normally lay their eggs in aphid colonies. The more brightly colored Paphiopedilum micranthum and Phragmipedium besseae are pollinated by Hymenoptera. Autogamy is limited but occurs most frequently in Phragmipedium species. About two-thirds of the insect-pollinated slipper orchids (25/37) have evolved highly specialized flowers that are pollinated by a single pollinator or several pollinator species in the same genus. Species belonging to the same taxonomic section usually have the same pollination system. The deceit-pollination system of Cypripedioideae appears to have evolved early in diversification of Orchidaceae.