Simaroubaceae are among the families whose circumscription radically changed over time, because phylogenetic analyses undertaken since 1995 demonstrated it was a polyphyletic group in its traditional delimitation. Currently, Simaroubaceae sensu stricto are a mostly pantropical, highly supported monophyletic group composed of 22 genera and approximately 120 species. Growing knowledge about members of the family has allowed several advances over the last couple of decades. The primary center of diversity for Simaroubaceae is in tropical America, and new contributions have been recently made regarding members of the family in the region, including descriptions of several new taxa. Hence, we undertook an updated overview of general information available for the group, with focus on American taxa of Simaroubaceae, and highlighting numerous data published after the 2011 monograph. Besides aiming to contribute to a better knowledge of a family with past controversial limits, we emphasize research topics in which the current scarcity of data demands further investigation.

An updated account of Simaroubaceae with emphasis on American taxa

Juglans mandshurica is a monoecious heterodichogamous species with protogynous and protandrous mating strategies that occur at a 1:1 ratio and are randomly distributed in the population. The inconsistent male and female flowering periods of the same mating type result in an imbalance of the ratio of male and female flowers, contributing to the low yield of this species. However, little more is known about its floral development. Following three consecutive years of observations, histological analysis, and scanning electron microscopy, we found that the morphological and anatomical development of the male and female flowers were synchronous. The male floral morphological development of J. mandshurica was divided into seven phases, while that of the female flower was nine. Four stages were shared between the male and female flower's anatomical development. Our findings indicate that there was minimal overlap between sexual functions within the same mating type, guaranteeing synchronization, mutual non-interference, outcrossing, and avoidance of self-fertilization. These results provide a theoretical basis for the improvement of fruit yield and quality through the reasonable allocation of protogynous and protandrous individuals in a population, and for artificial pollination control. Further, these findings lay a foundation for further research on the genetic mechanisms and environmental effects on flower development of heterodichogamous J. mandshurica.

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Flower Development of Heterodichogamous Juglans mandshurica (Juglandaceae).

What reproductive traits tell us about the evolution and diversification of the tree-of-heaven family, Simaroubaceae

Flowers of Meliaceae are traditionally described as bisexual, but functionally unisexual flowers have been reported for many genera. For Trichilia, several reproductive systems have been previously reported: subdioecy, gynodioecy, polygamy and hermaphroditism. The aim of this study was to analyze the occurrence of floral dimorphism and sexual-functional aspects of the flower of Trichilia claussenii. Structural and developmental analyses of flowers of Trichilia claussenii were performed using light and electron microscopy. In addition, male and female function of flowers was investigated through pollen viability and stigma receptivity tests, hand pollination and seed germination. Two floral morphotypes were identified in Trichilia claussenii: one morphologically male with a reduced gynoecium and the other morphologically female with anthers which do not release pollen. In the supposedly male flower, anthers are well developed and produce viable pollen grains. A conspicuous nectary disk differentiates at the base of the gynoecium, and the ovary has small ovules; however, our study proved that this ovary develops into a fruit, which contains viable seeds. In contrast, the supposedly female flower has larger gynoecium and ovules, and the nectary is smaller and inconspicuous. The stamens of female flowers have inviable pollen grains due to a tapetal necrotic product that keeps them united into an amorphous mass within the anthers. Male flowers are geitonogamous. Our results demonstrate that Trichilia claussenii exhibits subtle sexual floral dimorphism with female flowers and bisexual flowers distributed in different individuals. Our results indicate that male sterility occurs in only one morphotype; therefore, the species is gynodioecious.

Gynodioecy in Trichilia (Meliaceae) and a peculiar case of male sterility due to tapetal necrotic cell death

Anther and gynoecium structure and development of male and female gametophytes of Koelreuteria elegans subsp. formosana (Sapindaceae): Phylogenetic implications

Adan Alberto Avalos

Papers

Anther and gynoecium structure and development of male and female gametophytes of Koelreuteria elegans subsp. formosana (Sapindaceae): Phylogenetic implications