a b s t r a c tBignoniaceous woody species are very important ecological components of neotropical forests, but the reproductive biology of many species, such as Cybistax antisyphilitica, remains virtually unknown. Most species of Bignoniaceae are characteristically self-sterile, despite typically exhibiting normal pollen tube growth throughout the style, combined with slow rates of ovule penetration, fertilisation and endosperm initiation in selfed pistils. Uniform abortion occurs within a few days of anthesis, indicating the occurrence of late-acting self-incompatibility (LSI). However, breeding system studies have been performed in fewer than 7% of species, and other types of breeding systems (e.g., self-compatibility and apomixis) have been reported in this family. In the present study, the reproductive biology of C. antisyphilitica was investigated by field observation of flower visitors and floral events. Moreover, reproductive biology of this species was examined through experimental pollinations, analyses of pollen tube growth and ovule penetration using fluorescence microscopy, verification of pistil longevity, and a histological analysis of unpollinated vs. self-pollinated pistils. Finally, morphological aspects, quantities and germination were investigated in seeds that resulted from different pollination treatments. Natural pollination was effected by largeand medium-sized bees, and their visiting behaviour favours a high proportion of geitonogamy and no pollen limitation. Self-pollinated flowers produced no fruits, and all of the characteristic post-pollination events cited above were verified, witnessing the occurrence of LSI with post-zygotic rejection of selfed pistils in C. antisyphilitica. Although some indications of extended pistil longevity were found in selfed pistils, this feature seemed to be affected by unidentified environmental factors. The seeds were always monoembryonic and with high viability. A larger variation in the number of viable seeds was found in fruits derived from natural pollination. A low fruit set was observed after both natural and crosspollination, and most crossed fruits underwent abortion at several points during the juvenile phase, even when protected against herbivory. The formation of surplus flowers/juvenile fruits and the apparently wasteful selfing mechanism control implied in LSI are discussed in the context of the perennial life style of tropical woody plant species.

Editor: Maria von BalthazarPremise of research. Recent phylogenetic studies placed nearly all Neotropical arboreal and shrubby species of the Bignoniaceae (excluding Jacaranda) in the Tabebuia alliance, a clade that includes all of the woody species in this family with palmately compound leaves. However, the taxa assigned to this clade have appeared in these studies as an unresolved trichotomy with Sparattosperma as its sister group. Considering the diversity and taxonomic significance of ovule morphogenesis in the extant angiosperms, this study aimed to contribute to the systematics of the Bignoniaceae by investigating ovule ontogeny in one representative of each clade of the Tabebuia alliance trichotomy: Crescentia cujete, Cybistax antisyphilitica, and Tabebuia roseoalba.Methodology. The analysis is based on light microscopy observations of microtome semiserial sections of ovaries and ovules at several stages of development.Pivotal results. The ovules are anatropous, unitegmic, and tenuinucellate and originate from trizonate ovule primordia. The single integument shows a concurrent epidermal and subepidermal origin, and a dark staining hypostase develops at the chalaza. Meiosis of the megaspore mother cell results in a linear or T-shaped tetrad of megaspores. The chalazal megaspore generates a monosporic Polygonum-type female gametophyte. In comparison to previous studies, our analysis of ontogenetic events demonstrates that embryological features are highly conserved in the Bignoniaceae. However, some peculiar characteristics are congruent with the systematic consideration of this study, especially the pattern of callose wall deposition during megasporogenesis and the occurrence of a protruding versus nonprotruding nucellus during early ovule development. Conclusions.In the context of other embryological studies of the Bignoniaceae, our results support closer phylogenetic relationships among Crescentia, Handroanthus, and Tabebuia in comparison to Cybistax and indicate that the nonprotruding early nucellus is an additional character state that helps to segregate Tabebuia s.s. from other taxa in the Tabebuia alliance with a eusyncarpous ovary.