Embryology of Petrosavia (Petrosaviaceae, Petrosaviales): evidence for the distinctness of the family from other monocots

Abstract

The affinities of Petrosavia, a rare, leafless, mycoheterotrophic genus composed of two species indigenous to East to Southeast Asia, have long been uncertain. However, recent molecular analyses show that the genus is sister to Japonolirion osense. Japonolirion and Petrosavia comprise the Petrosaviaceae, which are now placed in its own order, Petrosaviales, distinct from other monocots based on molecular analyses. We conducted an embryological study of Petrosavia, comparing it to Japonolirion, as well as to basal monocots (Acorus and Araceae) and more derived monocots (Nartheciaceae, Velloziaceae, and Triuridaceae). Our results showed that Petrosavia is very similar in embryology to Japonolirion, with both genera sharing a glandular anther tapetum, simultaneous cytokinesis in microspore mother cells, anatropous and crassinucellate ovules, T-shaped tetrads of megaspores, ab initio Cellular-type endosperm, and a mature seed coat composed of the exotesta, endotesta, and endotegmen. The two genera of Petrosaviaceae are clearly distinct from Acorus, and all Araceae, Nartheciaceae, Velloziaceae, and Triuridaceae genera in various combinations of characters. Thus, both molecular and embryological evidence support the distinctness of the Petrosaviaceae from other monocots and its placement in its own order, Petrosaviales.

A revision of the family Petrosaviaceae in Vietnam

“…Traditionally, these two genera were never regarded as closely related, until their affinity was established using molecular data (Fuse and Tamura , Cameron et al 2003 , Davis et al , Chase et al , Graham et al , Hertweck et al ). Despite their strong dissimilarity, these two genera share some special embryological features such as T‐shaped megaspore tetrads (Tobe and Takahashi ).…”

Endosperm development in the Araceae (Alismatales) and evolution of developmental modes in monocots

“…Currently, 14 families are recognized in the Alismatales, and 94 families are recognized in the monocots as a whole (Stevens 2001 onwards;Haston et al 2007), although the Angiosperm Phylogeny Group (2009) has reduced the number of monocot families to 78 by broadening circumscription of a few families. Among these, 13 of the 14 families of the Alismatales, as well as 62 of the 94 monocot families, are known with respect to developmental modes of the endosperm (data for Acorales from Floyd and Friedman 2000; for data of individual families of the Alismatales see Appendix 1; data for Petrosaviales from Tobe and Takahashi 2009; data for individual families of the remaining orders mainly from Johri et al 1992;Takhtajan 2009). …”