A linear classification of Cyperaceae

This paper provides a linear classification of two subfamilies, 24 tribes, 10 subtribes and 95 genera of the monocot family Cyperaceae (Poales), based on a stable phylogenetic framework resulting from years of morphological, molecular phylogenetic and phylogenomic studies. The family includes c. 5687 species. The most species-rich tribes are the monogeneric tribe Cariceae with c. 2003 species, and tribe Cypereae with c. 1131 species. The highest generic diversity is found in tribe Schoeneae (25 genera), which resulted in the recognition of eight subtribes to facilitate studying this group. The linear classification will help the organisation of Cyperaceae specimens in herbaria according to a systematic order and provides an easy-to-use summary of the current classification of the family.


Introduction
To support curation in herbaria opting to organise their collections in accordance with phylogenetic relationships among genera, and to provide an easy-to-use summary for a variety of audiences, a linear sequence of Cyperaceae is published here. Linear sequences reflect the order of names attached to the tips of a phylogenetic tree, after the branches in the tree have been ordered according to some projection method (Chatrou et al. 2018). The methodology for translating tree-like relationships into a linear sequence published by Haston et al. (2007) is followed. Linear sequences are available for vascular plants (Wearn et al. 2013), lycophytes and ferns (Christenhusz et al. 2011a), extant gymnosperms (Christenhusz et al. 2011b), angiosperms (Haston et al. 2007(Haston et al. , 2009, and several plant families including Annonaceae (Chatrou et al. 2018) and Fabaceae (Lewis et al. 2013).
Following Chatrou et al. (2018), the following steps were taken to assemble the phylogenetic tree underpinning the linear sequence, and to translate the tree into the sequence: (1) Largely based on the results of Larridon et al. (2021a), a summary tree showing relationships of all genera of Cyperaceae was assembled. Details are given below in the section 'Cyperaceae classification'. (2) Clade size was defined in terms of number of species, with species numbers for all genera based on Larridon et al. (2021a). (3) Nodes of the phylogenetic tree were rotated so that clades with fewer species were placed before clades with more species following Haston et al. (2007). This clade size criterion was applied to all nodes in the tree, starting from the root node (Fig. 1). As a result, the names along the tips from top to bottom represent the linear sequence.

Cyperaceae classification
A recent paper provided a new classification of Cyperaceae at tribal, subtribal and generic level (Larridon et al. 2021a) based on targeted sequencing data obtained with the Angiosperms353 probe kit (Johnson et al. 2019) to build a well-supported phylogenetic framework for the family. Only eight genera could not be placed in the phylogenomic study, for five of which (Ammothryon R.L.Barrett, K.L.Wilson & J.J.Bruhl, Blysmopsis Oteng-Yeb., Blysmus Panz. ex Schult., Capeobolus Browning, Didymiandrum Gilly) their phylogenetic placement is known based on previous Sanger sequencing-based studies (e.g. Larridon et al. 2018a;Semmouri et al. 2019;Barrett et al. 2021a;Costa et al. 2021). For Nelmesia Van der Veken and Trichoschoenus J.Raynal, both monotypic genera only known from a single collection, placement was decided based on (embryo) morphology and b i o g e o g r a p h y ( L a r r i d o n e t a l . 2 0 2 1 a , b ) . Rhynchocladium T.Koyama is the only genus that remains unplaced.
In tribe Abildgaardieae, the circumscription of the genera Bulbostylis Kunth and Fimbristylis Vahl has changed. Recently, the small mainland African genus Nemum Desv. was synonymised with Bulbostylis (Roalson et al. 2019a;Larridon et al. 2019), and the Australian monotypic genus Crosslandia W.Fitzg. was sunk into Fimbristylis (Roalson et al. 2019b). Furthermore, a new genus Zulustylis Muasya was published for two species previously placed in Fimbristylis (Muasya et al. 2020). Lastly, a new genus Scleroschoenus K.L.Wilson, J.J.Bruhl & R.L.Barrett was published to encompass Australian species previously placed in Actinoschoenus Benth., but clearly forming their own lineage related to two other Australian genera, Arthrostylis R.Br. and Trachystylis S.T.Blake (Larridon et al. 2021b).
The biggest taxonomic changes at generic level occurred in tribe Cypereae. After the now monotypic tribe Cariceae, it is the second most species-rich tribe in Cyperaceae with well over 1100 species (Larridon et al. 2021a). Before the molecular era, the tribe Cypereae was circumscribed based on embryo morphology; all species included in this tribe have either a Cyperus type embryo or similar Ficinia type embryo (Goetghebeur 1998;Semmouri et al. 2019). Studies have shown that embryos provide some of the best morphological characters to delimit Cyperaceae groups that agree with molecular phylogenetic results (Semmouri et al. 2019). Two clades are distinguished  (Larridon et al. 2021b). The number of species for each genus is indicated. Bars on the right indicate tribal classification in tribe Cypereae, the Ficinia Clade or subtribe Ficiniinae and the Cyperus Clade or subtribe Cyperinae (Larridon et al. 2021a). Ficiniinae species are predominantly characterised by having spikelets with spirally arranged glumes. In contrast, species of the Cyperinae usually have spikelets with distichous or two-ranked glumes. Besides Cyperus sensu stricto, 13 segregate genera as circumscribed by the classification of Goetghebeur (1998) belong to Cyperinae (Larridon et al. 2021a). Molecular phylogenetic studies revealed that these segregate genera are all nested within Cyperus sensu stricto and that several of them do not form natural groups (Larridon et al. 2011a(Larridon et al. , 2013Bauters et al. 2014). As a result, their species were recently transferred to Cyperus (Larridon et al. 2011b(Larridon et al. , 2014Bauters et al. 2014;Pereira-Silva et al. 2020).
Recently, efforts have been made to realign the taxonomy of some of the larger tribe Schoeneae genera, i.e. Costularia C.B.Clarke, Epischoenus C.B.Clarke, Schoenus L., Tetraria P.Beauv. and Tricostularia Nees, to make them monophyletic. In tribe Scirpeae, the Linnean genus Scirpus L. was very heterogenous (Starr et al. 2021). Based on molecular phylogenetic and embryo morphology data, a series of new genera were described (e.g.

Acknowledgements
This work could not have been completed without the support of the international Cyperaceae research community, recently united as the International Sedge Society. I would like to acknowledge their collaboration and support during the past 15 years.
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