Reproductive biology and pollination of Utricularia reniformis A.St.‐Hil. (Lentibulariaceae)

Abstract

Utricularia reniformis is an endemic Brazilian carnivorous plant, most common in high-altitude grasslands. Knowledge of the reproductive biology of U. reniformis is essential for planning conservation strategies, but it is currently poorly understood. Thus, we studied the floral morphology, floral biology, breeding system and pollination of this species. U. reniformis produces and stores nectar in the flower spur, a classic feature of bee-pollinated flowers, and we recorded Xylocopa sp. and Bombus sp. as pollinators. Moreover, although it is self-compatible it is an obligate animal-pollinated species, as the sensitive stigma avoids self-pollination. However, in natural conditions reproductive success is low due to the rarity of visits from pollinators. We suggest that the low reproductive success caused by a deficit of pollinators may affect gene flow, causing loss of genetic diversity in U. reniformis.

Floral ultrastructure of two Brazilian aquatic-epiphytic bladderworts: Utricularia cornigera Studnička and U. nelumbifolia Gardner (Lentibulariaceae)

“…show great variation in the size and, in particular, the length of their nectary spurs (Taylor 1989). Both species investigated here, as well as U. reniformis , possess large and relatively long spurs which can be accessed easily by long-tongued bumblebees, as has been demonstrated for this last taxon (Clivati et al 2014). Peltate glandular trichomes are present in the nectary spurs of U. cornigera and U. nelumbifolia and, in U. nelumbifolia , are arranged in two tracts coinciding and seemingly closely associated with the main vascular bundles supplying the apical part of the nectary spur.…”

“…Indeed, both the colour and shape of the palate of U. cornigera and U. nelumbifolia also resemble those of U. reniformis , a species which, according to Clivati et al (2014), based on testing tissues with aqueous neutral red solution, lacks osmophores (although this may simply be due to the hydrophobic nature of the epidermal surface). Recently, we proposed that the floral glandular hairs of U. dunlopii P. Taylor, a member of sect.…”

“…Furthermore, observations reported here indicate that the cuticle overlying the heads of these trichomes becomes distended in response to the subcuticular accumulation of nectar, as what occurs in the nectaries of other unrelated taxa (Nepi 2007 and references therein). The trichomes lining the spur of U. cornigera and U. nelumbifolia (comprising a basal cell, a central cell whose walls stain selectively with Sudan stains and may thus act as a hydrophobic barrier and a multicellular head) are typical of the genus and occur in all three subgenera ( Polypompholyx , Bivalvaria and Utricularia sensu Müller and Borsch 2005), as well as various sections, such as Pleiochasia ( U. dichotoma , U. paulinae , U. dunlopii— Płachno et al 2015), Oligocista ( Utricularia arcuata— Farooq 1963; U. reticulata , Utricularia scandens —Farooq and Siddiqui 1966), Utricularia ( Utricularia gibba , Utricularia inflata —Farooq and Siddiqui 1966; U. inflexa —Farooq 1963), Vesiculina ( Utricularia purpurea —Farooq and Siddiqui 1966) and Iperua ( U. reniformis —Clivati et al 2014; U. cornigera and U. nelumbifolia —the subjects of the present paper). Thus, it would appear that nectar-secreting trichomes in the genus Utricularia are very conservative in evolutionary terms.…”

“…Furthermore, some have formed the subject of embryological (Płachno and Świątek 2012), seed and seedling structure (Studnička 2009; Płachno and Świątek 2010; Menezes et al 2014), ecological (Studnička 2011) and genetic studies (Clivati et al 2012). With the sole exception of U. reniformis (Clivati et al 2014), detailed observations of plant–pollinator interactions are lacking for these species. Pollination of the small, terrestrial species Utricularia albocaerulea Dalz., Utricularia graminifolia Vahl.…”

“…and Bombus sp.) have been recorded for U. reniformis (Clivati et al 2014). Recently, however, it was proposed that in the Australian species Utricularia dunlopii , where the nectary spur is reduced, pollinators are attracted largely by the insectiform configuration of the flower and volatilization of fragrance putatively produced by glandular trichomes (osmophores) densely distributed upon the modified floral appendages (Płachno et al 2015).…”