Pollen morphology of Waltheria L. (Malvaceae-Byttnerioideae) from Bahia, Brazil

Abstract

Waltheria encompasses about 60 species distributed in Brazil and Mexico. To improve the palynology of the genus, we analyzed 14 species occurring in the Brazilian State of Bahia. Pollen grains were acetolyzed and examined using light microscopy and scanning electron microscopy. Non-acetolyzed pollen grains were viewed by transmission electron microscopy. Th e results revealed two general pollen types based on exine ornamentation, such as reticulate and echinate, which are distinct with regard to (1) size and shape, (2) apertural type and number, (3) relative length of ectoapertures, and (4) thickening of the nexine compared to the sexine. An ultrastructural analysis of the pollen wall revealed a continuous foot layer and a compact and discontinuous endexine in most cases. Th e sexine consisted of heterogeneous columellae, which support a perforated semitectum (echinate type) or the semitectum was composed of perforations and muri-shaped thickening (reticulate type). Th ese results confi rm a high degree of pollen dimorphism in Waltheria associated with heterostyly.

Phylogenomics resolves deep subfamilial relationships in Malvaceaes.l.

“…/Dombeyoideae are characterized by bilobed cotyledons, a short staminode tube, and large-sized, echinate pollen grains with 3-zonoporate apertures ( Falque et al 1992 ; Stevens 2001 ; Bayer and Kubitzki 2003 ; Perveen and Qaiser 2009 ; Hamdy and Shamso 2010 ; Silveira Júnior et al 2017 ). /Tilioideae have been characterized by their pollen structure (“tilioid pollen type”; Chambers and Godwin 1961 , 1971 ; Bayer and Kubitzki 2003 ; Le Péchon and Gigord 2014 ), and the presence of folded cotyledons and staminodes opposite the petals have also been highlighted as potential synapomorphies ( Figure 3 ; Stevens 2001 ; Bayer and Kubitzki 2003 ; Judd et al 2008 ).…”

Floral polymorphism and heteromorphic incompatibility in the distylous tropical shrub Waltheria rotundifolia (Malvaceae)

“…Pollen grains were extracted from the anthers of these flowers to evaluate the presence of morph‐specific differences in size ( N = 120 grains). Since pollen grains of W. rotundifolia are spherical and apolar (Silveira et al, 2017), differences in pollen size between morphs were evaluated by measuring their diameter through digital photographs using a Motic BA310 optical microscope (Richmond, British Columbia, Canada) equipped with a digital camera. To evaluate pollen production of each morph, 10 flower buds per morph ( N = 20 flowers) were collected.…”

“…The small distylous flowers are comprised of a bright yellow corolla with five petals, five stamens whose filaments are fused and enclosing the style, and high-level organs exerted about 2 mm from the corolla (Figure 1a, b). Dimorphism in pollen size, exine ornamentation and thickness, and aperture shape has been described for W. rotundifolia (Köhler, 1976;Silveira et al, 2017). The fruit is a triangular capsule, 1.7-2.3 mm long and 1.7-2.0 mm wide, which produces one seed (Saunders, 1995).…”

“…Around 83% of species in the genus Waltheria are distylous (Saunders, 1995). Nonetheless, beyond the evidence of wide variation in pollen ancillary polymorphisms in some species (Köhler, 1976; Saba & Santos, 2015; Silveira et al, 2017), only one study has evaluated the level of reciprocity and the presence of heteromorphic incompatibility (Bramow et al, 2013). Moreover, information about the efficiency of distyly promoting legitimate pollination is lacking.…”

Floristic characterization and pollen morphology of plants visited by Apis mellifera L. in caatinga areas in Bahia, Brazil

“…They observed similar characteristics regarding the medium (short-and longstyle morphs) to the large size of the grains (long-style morph) and the oblate-spheroidal (short-and long-style morphs) to spheroidal shape (long-style morph). Saba et al (2004) andSilveira-Júnior et al (2017) describe the pollen grains for the studied species of Waltheria (Malvaceae). However, their descriptions for homostylic W. indica differ from the one presented by us, especially regarding pollen grain shape and size.…”