Floral anatomy and development of Saxofridericia aculeata (Rapateaceae) and its taxonomic and phylogenetic significance

Abstract

Floral anatomy and development of Saxofridericia aculeata Körn was studied in a comparative approach to contribute to the understanding of the family. Flowers at different developmental stages were analysed with light and scanning electron microscopy, and the nature of the exudate secreted by the floral trichomes was investigated by histochemical tests. The anatomical characteristics observed in S. aculeata flowers were compared with those from other Rapateaceae species by a cluster analysis (UPGMA). The dendrogram generated reflects the groupings that emerged in phylogenetic molecular analyses, highlighting the usefulness of floral anatomy for taxonomy and for the understanding of infrafamilial relationships. The exudate secreted by the trichomes has a polysaccharidic composition. Such trichomes (colleters) occur in the sepals, petals, filaments and around the gynoecium; they are initiated at mid-stage of floral development and are an apomorphy of the family. The flowers are pentacyclic, presenting three initially free sepals, petals, stamens and carpels that mature in a centripetal order. The connate portion of the corolla, which is also adnate to the stamens, has a late development by zonal growth. Gynoecium formation is a combination of postgenital and congenital fusion processes. Data on floral organogenesis of Rapateaceae are first reported here and support the early diverging position of the family in Poales, close to Bromeliaceae.Keywords Cluster analysis Á Colleter Á Monotremoideae Á Postgenital intercarpellary fusion Á Rapateoideae Á

More than Scales: Evidence for the Production and Exudation of Mucilage by the Peltate Trichomes of Tillandsia cyanea (Bromeliaceae: Tillandsioideae)

“…Many of the features presented by the secretory trichomes of T. cyanea , particularly the restriction of secretory activity to young portions and the mucilaginous nature of the exudate, allow their classification as colleters. This functional concept of colleter has been attributed to numerous secretory systems of this type, especially in the face of the recent descriptions of glands associated with juvenile organs in monocots [ 16 , 31 , 34 , 35 , 38 , 39 ]. Such glands seem to perform the same functions as traditional colleters, but usually lack the typical and relatively more complex structure often found in eudicotyledons [ 36 ].…”

“…A role in protection against desiccation is a recognized function of some exudates in young reproductive axes of angiosperms [ 31 , 34 , 38 , 39 , 52 , 69 ] in which water supply via xylem may be inefficient, and secretions could avoid water loss due to excessive transpiration or increase water uptake through the cuticle [ 45 , 47 , 69 ]. In this context, an additional role in water absorption must be considered concerning the trichomes of T. cyanea due to their similarity with the absorbing scales of bromeliad leaves, with which they share many structural features related to water uptake ability.…”

“…The functions associated with the secretion in A. blanchetiana appear to be the same as those attributed to the activity of colleters. These structures are currently characterized from a functional point of view as glands that produce and release mucilaginous or resinous secretion for protection against desiccation or herbivore/pathogen attack in young parts of the plant [ 16 , 31 , 32 , 33 , 34 , 35 ]. While colleters are widely distributed in eudicotyledons [ 36 ], their presence has been demonstrated in only a few monocot families [ 16 , 31 , 33 , 34 , 35 , 37 , 38 , 39 ].…”

Flower and Spikelet Construction in Rapateaceae (Poales)

“…For example, species of Rapatea, Saxofridericia and Stegolepis are reportedly exclusively buzz pollinated by female euglossine bees (Renner, 1989;Hentrich, 2008;Krahl et al, 2020). However, intercarpellary slits that resemble septal nectaries were reported in young flowers of Saxofridericia aculeata (Ferrari and Oriani, 2017). The presence of septal nectaries is widely inferred for the three genera of Schoenocephalieae (Guacamaya, Kunhardtia and Schoenocephalium), based on the presence of abundant nectar and visits by hummingbirds (Givnish et al, 2000;Berry, 2004), though pollination is not well-documented in these species (Fernández-Lucero et al, 2016).…”

“…The presence of septal nectaries is widely inferred for the three genera of Schoenocephalieae (Guacamaya, Kunhardtia and Schoenocephalium), based on the presence of abundant nectar and visits by hummingbirds (Givnish et al, 2000;Berry, 2004), though pollination is not well-documented in these species (Fernández-Lucero et al, 2016). However, anatomical studies to date have failed to convincingly confirm the presence of septal nectaries in these taxa (Colella-Franco, 1999;Oriani and Scatena, 2013;Ferrari and Oriani, 2017). Venturelli and Bouman (1988) reported open septal nectaries (intercarpellary slits) in the ovary of Spathanthus unilateralis (Rapateoideae), but this observation was not confirmed in a subsequent study (Oriani and Scatena, 2013).…”