A Review of the Distribution of Plasmodial and Invasive Tapeta in Eudicots

Abstract

The tapetum, a nutritive tissue necessary for microspore development, is of two basic types in angiosperms: secretory and plasmodial. A third type, invasive nonsyncytial, is possibly intermediate. Secretory tapeta are plesiomorphic in angiosperms, and plasmodial and invasive tapeta are derived types that have evolved several times in early‐divergent angiosperms and particularly in monocots. Many eudicots have secretory tapeta. In this article, records based on new observations for plasmodial and invasive tapeta in eudicots are presented, together with a literature survey. The data indicate that these tapetal types have evolved independently several times in eudicots, particularly in later‐branching lineages. They are rare in early‐divergent eudicots, where they occur only in Berberis and Mahonia (Berberidaceae: Ranunculales). They are recorded in some Amaranthaceae s.l. (Caryophyllales) and in some rosids. Plasmodial and invasive tapeta are more frequent in asterids, where they occur in several families, together with the secretory type. Plasmodial tapeta predominate in Asteraceae (Asterales) and Caprifoliaceae s.l. (Dipsacales). In eudicots, tapetum type is often variable within families or even genera, unlike in early‐divergent angiosperms and especially monocots, where a single tapetum type usually characterizes families or orders. In eudicots, the plasmodium usually forms after the microspores are released from the tetrads, unlike in monocots, where it forms earlier, surrounding the tetrads.