Abstract Despite recent advances in molecular phylogenetic studies, deep evolutionary relationships in Cyperaceae are still not entirely resolved. Reduction of floral morphology and complex inflorescences pose difficulties to unravel relationships based on morphology alone. One of the most phylogenetically informative structures in Cyperaceae are the embryos. The utility of embryo characters and types in Cyperaceae systematics is reviewed in a molecular phylogenetic context using a DNA supermatrix incorporating sequences from five plastid (matK, ndhF, rbcL, rps16, trnL-Y) and two nuclear ribosomal (ETS, ITS) regions. The phylogenetic hypothesis presented includes the most extensive sampling of the family to date. Fourteen qualitative morphological embryo characters were coded, ancestral state reconstructions were performed, and the embryo of each sampled genus was classified in a typological system based on key morphological features. Embryo morphology provides a valuable source of independent data for Cyperaceae systematics that can be used to place species with unknown affinities, when molecular data is not available, or when results of analyses are inconclusive or conflicting. Integrating embryo data will remain critical for future higher level studies of Cyperaceae evolution and classification.

Keywords Ancestral state reconstruction * Cyperaceae * Embryo * Evolution * Molecular phylogenetics * Systematics

Introduction

Cyperaceae (sedges) represent the third largest monocot family in terms of species diversity, after Orchidaceae (orchids) and Poaceae (grasses), with c. 90 genera and c. 5,500 species (Govaerts et al. 2018). The family has an almost cosmopolitan distribution (Simpson et al. 2011), and occupies a broad range of habitats from rain forests to tundra (Bruhl 1995; Smith et al. 2009; Simpson et al. 2011). Although generic diversity is greatest in the tropics, its largest genus Carex L. is one of the most species-rich genera in temperate regions (Global Carex Group 2015). Sedges are often seen as rather uniform and grass-like, probably because they are represented by perennial herbs in the temperate regions of the northern hemisphere. However, sedges are phenotypically very diverse in the tropics with some species even forming shrubs and lianas (Goetghebeur 1998; Naczi and Ford 2008). Cyperaceae are of global economic and ethnobotanical significance (Simpson and Inglis 2001), and are often keystone species in wetlands (e.g. Larridon 2011) and in temperate, arctic or alpine grasslands (e.g. Grabherr 1989; Small and Cayouette 2016). Molecular phylogenetic studies recovered two main clades in the Cyperaceae, corresponding to the subfamilies Mapanioideae and Cyperoideae (Simpson et al. 2007; Muasya et al. 2009a). Although recent studies have provided new insights into sedge relationships (e.g. Larridon et al. 201 la, 2013; Bauters et al. 2014, 2016; Leveille-Bourret et al. 2014, 2018a, b; Global Carex Group 2015; 2016), several deep nodes remain unresolved or contentious. The reduced floral morphology and complex inflorescences of sedges pose difficulties for unraveling evolutionary relationships based on morphology alone (Bruhl 1995; Muasya et al., 2009a, b). Macroscopic and traditional anatomical characters are often uninformative at deep phylogenetic levels because of uncertain homology between structures in different groups and high levels of homoplasy, encouraging the search for other characters to resolve taxonomic problems within...