Complex patterns of morphogenesis, embryology, and reproduction in Triuris brevistylis, a species of Triuridaceae (Pandanales) closely related to Lacandonia schismatica

Abstract

Triuris brevistylis Donn. Sm. (Triuridaceae: Pandanales), a mycoheterotrophic monocotyledon with populations in Mexico and Guatemala, is closely related to Lacandonia schismatica E. Martínez et C. H. Ramos, a triurid species displaying a peculiar “inside-out” arrangement in its reproductive axes. Triuris brevistylis is a polygamodioecious species in which four types of bisexual ramets–genets coexist besides regular (i.e., unisexual) male and female flowers. Here, we characterize the embryology of three of the following different types of reproductive axes in T. brevistylis: male and female flowers and a bisexual floral type in which stamens develop at the base of the receptacle of an otherwise female-looking flower. Through this embryological characterization, we have detected that cleistogamy, a mechanism previously considered exclusive to L. schismatica, occurs in the bisexual flowers. Besides serving as characters for the systematics of Triuridaceae and Pandanales, our data establish that morphogenetic and reproductive patterns in T. brevistylis are more complex than in L. schismatica. Therefore, we claim that our results contribute to a refined assessment of the controversy regarding morphological interpretation of reproductive axes in triurids.