Flower palate structure of the aquatic bladderworts Utricularia bremii Heer and U. minor L. from section Utricularia (Lentibulariaceae)

Abstract

There is an enormous diversity in the structure of the flower palate of the carnivorous rootless genus Utricularia. This study aims to examine the structure of the palates in Utricularia bremii Heer and U. minor L of the Utricularia sect. Utricularia, which have a glandular palate type. In both species, the palate has only one type of glandular trichomes. Because of the occurrence of cell wall ingrowths in its glandular cells, any exudation may be transported via eccrinous secretion. It was proposed that the palate trichomes of the examined species act as scent glands and that the palate may play a role as an unguentarium. Both U. bremii and U. minor are of an open flower type. Thus, U. bremii and U. minor flowers can be penetrated by small, weak insects, which then easily have access to their generative structure. Small Hymenoptera (member of families Mymaridae and Braconidae) were observed as flower visitors of the male-sterile species Utricularia bremii.

Nectar trichome structure of aquatic bladderworts from the section Utricularia (Lentibulariaceae) with observation of flower visitors and pollinators

“…The ultrastructural characters of the examined trichomes are very similar when compared with the scent glands from the palate of U. bremii (Płachno et al 2017a) and the corolla appendages of U. dunlopii (Płachno et al 2016). In all Utricularia species examined here, the nectary trichome had a barrier cell (pedestal cell) with a thick radial wall, which was impregnated with a lipophilic material.…”

“…However, it should be added that the barrier cell is the common character of various secretory trichomes of Lentibulariaceae (e.g. Fineran and Lee 1975; Fineran and Gilbertson 1980; Fineran 1985; Płachno et al 2007, 2017a). …”

“…Płachno et al (2017a) observed that small Hymenoptera (members of families Mymaridae and Braconidae) were flower visitors of U. bremii . They suggested that these Hymenoptera might also be pollinators of U. minor , which has a similar size and flower structure to those of U. bremii .…”

Flower palate ultrastructure of the carnivorous plant Genlisea hispidula Stapf with remarks on the structure and function of the palate in the subgenus Genlisea (Lentibulariaceae)

“…For example, species that have small flowers such as U. albocaerulea , U. purpurascens and U. reticulata (Hobbhahn et al 2006) were visited by various insects: bees, butterflies, moths and flies, and some species of Hymenoptera, which were effective pollinators. In Utricularia bremii , small Hymenoptera (Mymaridae, Braconidae) were observed as flower visitors (Płachno et al 2017a). The large flowered Utricularia species, e.g.…”

“…In Utricularia flowers, the palates are morphologically very diverse (Taylor 1989) and probably play a key role in providing the colour, mechanical and olfactory stimuli to attract insect pollinators and to guide them to their generative structures and the spur with nectar (Płachno et al 2016, 2017a,b). The palates in Genlisea also provide the colour signals for pollinators (Fleischmann 2012); however, information about the micro-morphology of Genlisea palates is scarce.…”