Rhizome structure and evolution in the ant-associated epiphytic fern Lecanopteris Reinw. (Polypodiaceae)

Abstract

The Lecanopteris rhizome is expanded or hollow, and is used as a nest by ants of the genera Iridomyrmex and Crematogaster. The 13 species of Lecanopteris display six rhizome forms, unequally distributed between two subgenera. Subgenus Myrmecopteris comprises four species, each possessing a characteristic rhizome: L. mirabilis has a solid, arched rhizome, with the domatium between the rhizome underside and host trunk; L. sarcopus displays dimorphism between solid frond-bearing axes and hollow, frondless side branches; the rhizome of L. Crustacea is hollow but phyllopodia are solid; L. sinuosa has hollow rhizomes and phyllopodia. The architecture of L. mirabilis, L. sarcopus and L. Crustacea results in a compact, many-layered domatium, but L. sinuosa has a tittle-branched habit. Members of subg. Lecanopteris are completely hollow and have a compact architecture: six species typified by L. pumila have a central gallery and hollow phyllopodia, and three species typified by L. darnaedii have two gallery and chamber systems. The genus Lecanopteris is unlikely to be monophyletic; its nearest relative is Phymalodes. Phylogeny in subg. Myrmecopteris is unclear; no gradation of rhizome complexity exists. In subg. Lecanopteris, L. curtisii is considered most similar to the ancestral species, giving rise to the L. pumila group, which engendered the L. darnaedii group.