Seeds and indehiscent fruit of Anarthriaceae and Australian Restionaceae: a gallery of micromorphology

Abstract

The diaspores of Anarthriaceae and Australian Restionaceae are seeds or small nuts and are illustrated by scanning electron microscopy or multifocus microscopy and considered in relation to a previously published phylogeny based on plastid genes. Loculicidal trilocular capsular fruits are the basal condition in the restiid clade, but indehiscent fruits have evolved many times. In the Australasian members, indehiscent fruits are found in Anarthriaceae (Hopkinsia); Restionaceae: Centrolepidoideae (Aphelia); Sporadanthoideae (Calorophus); Leptocarpoideae (Empodisma, Winifredia and the whole of the Leptocarpus and Desmocladus clades). Seeds of dehiscent fruits show a diversity of surface ornamentation with distinctive surface patterns characterising genera such as Lyginia, Chordifex and Loxocarya. Pericarps are membranous in subfam. Centrolepidoideae but in the Leptocarpus clade range from hyaline in much of Leptocarpus to hard and woody in Alexgeorgea and Hypolaena. Pericarps are parenchymatous in most of the Desmocladus clade, but woody in Catacolea. Indehiscent fruits are mostly shed with tepals and floral bracts attached or, in Baloskion and some Lepidobolus species, also with the subtending glume. Seed weights were not comprehensively sampled but vary from 0.08 mg in Centrolepis to >600 mg in Alexgeorgea, with most in the range 0.3–3 mg [dry weight]. The smaller weights are mostly either in perennials of habitats with more reliable rainfall or in ephemeral annuals that avoid drought by their brief growing season, but the association between seed type and habitat has not been investigated. We see no convincing evidence to link to Restionaceae the fossil taxon Restiocarpum and the Milfordia pollen that occurs with it in Eocene–Oligocene sediments of Queensland.