Phylogenetic, Developmental and Functional Aspects of Stomatal Patterning: Lessons from Magnoliids

Abstract

The magnoliid clade encompasses 18 extant families arranged in four orders, plus several extinct taxa, including some of the most ancient angiosperm fossils. The clade is characterized by paracytic stomata with a distinct pair of lateral subsidiary cells that flank the guard cells, though other stomatal types are also reported, including anomocytic and anisocytic. In contrast with monocots, the paracytic stomata of magnoliids develop from linear triads, and the lateral subsidiary cells are stomatal-lineage ground cells (SLGCs). Anisocytic stomata typically possess three SLGCs. Amplifying divisions are rare in magnoliids, but occur in some Piperales, in association with anisocytic stomata. Differences in mature stomatal types result from differences in cell shape and polarity at critical developmental stages. Stomatal clusters have been reported in Cinnamomum (Lauraceae) and Galbulimima (Himantandraceae), but neither are apparently formed by amplifying divisions, in contrast with eudicots. In Galbulimima, each peltate scale hair is surrounded by a ring of 3–8 non-contiguous stomata, each derived from different initial meristemoids.