ASCOLEPIS, LIPOCARPHA & VOLKIELLA

October 2010 to June 2011, MSc thesis

Ascolepis, Lipocarpha and Volkiella are three highly specialised genera from tribe Cypereae (Cyperaceae). They are characterised by their reduced inflorescences, which consist of spikes of one-flowered spikelets. In Ascolepis and Lipocarpha these spikelets are spirally arranged along a rachis, while in Volkiella these spikes are placed distichously. An Ascolepis spikelet consists of a reduced spikelet bract and an enlarged, flower-bearing glume. A prophyll is never found in this genus. Lipocarpha and Volkiella have spikelets with a large spikelet bract and two hyaline scales: a prophyll and a flower bearing glume. In some species this glume and/or prophyll can be reduced or absent. Previously, no attempts were made to resolve the infrageneric relationships in these genera, although a relation between these three genera was already found in previous studies.

We made a phylogenetic hypothesis based on maximum likelihood and bayesian analyses of the sequences of three genetic markers. One nrDNA marker (ETS1f) and two chloroplast markers (trnH-psbA and rpl32-trnL) were used. Obtained PCR products were sequenced and manually aligned. Gaps were coded using the simple indel coding method. Maximum likelihood and bayesian analyses were performed for eight different data sets: one for each marker separately and one for a combined alignment. For trnH-psbA and rpl32-trnL analyses were also run on an alignment without coded gaps and for ETS1f an extra analysis was done were all amplified sequences were included.

In an ontogenetic study we focussed on three Lipocarpha species, more specifically their inflorescences were examined. Inflorescences were washed en treated so they could be placed in a critical point dryer. After this, they were prepared for SEM imaging. With this study we wanted to confirm the nature of the hypogynous scales as prophyll and glume in the spikelets. For Lipocarpha rehmannii we tested the hypothesis that this species is a highly reduced form of Lipocarpha, since our phylogenetic hypothesis contradicted this. This species, formerly placed in Rikliella, has no prophyll or glume.

In the most complex analysis, with the three markers combined and gaps coded, six clades are found in the core group of Lipocarpha. A seventh clade includes the former genus Rikliella and is found in the polytomy of C4 Cyperus, making Lipocarpha polyphyletic. The core group of Lipocarpha forms a paraphyletic group since the monotypic Volkiella is found in this clade. Ascolepis is divided in two clades but only the A. capensis - A. brasiliensis clade is well supported. Amplification of the different markers for Ascolepis did not work well and for most species only one marker was amplified. Therefore, it is difficult to draw conclusion from the phylogenetic hypothesis of Ascolepis.
The ontogenetic research clearly showed that the hypogynous scales of Lipocarpha are indeed a prophyll and a flower bearing glume. The inflorescence of a typical Lipocarpha consists of an indeterminate rachis with spirally placed spikelet bracts. Under these spikelets bracts one-flowered spikelets are found, with an abaxial prophyll and an adaxial flower bearing glume. De highly reduced flower consists of a gynoecium with two style braches (in the observed species) and one stamen. It became clear that the stamen develops first and the gynoecium starts to develop later, a process known as protandry. The inflorescence of Lipocarpha rehmannii consists of a spikelet with a thickened rachilla, on which flower bearing glumes are spirally arranged. So what was thought to be a spike, is in fact a spikelet and what was thought to be a spikelet bract, is a glume.

The six different clades in the core group of Lipocarpha, can be distinguished by some morphological characteristics, although these are scarce. The most reliable characters are the shape and measurements of the spikelet bract, the shape of the nutlet, the cross section of the nutlet and the number of style branches.
Ontogeny confirmed our phylogenetic hypothesis on the L. rehmannii inflorescence. We can conclude from this that the L. rehmannii inflorescence consists of a spikelet with spirally arranged glumes. This contradicts the reductional hypothesis of a Lipocarpha spikelet over a Hemicarpha spikelet towards a Rikliella spikelet.
The three genera studied are all part of the C4 Cyperus clade. This clade forms a monophyletic group in a paraphyletic C3 Cyperus. Relationships in C4 Cyperus are poorly understood. For these reasons all segregated genera in C4 Cyperus are nested in Cyperus. For all species of Ascolepis, Lipocarpha and Volkiella a new Cyperus name is proposed here. The core group of Lipocarpha (including Volkiella) form the Lipocarpha clade. In this Lipocarpha clade, we recognise three different sections. The species formerly included in Rikliella form a different section: Cyperus section Rikliella. Since Ascolepis is a monophyletic group it is now named as Cyperus section Ascolepis.

From this MSc thesis we conclude that Lipocarpha is polyphyletic with a core group of six clades (in which also Volkiella is found). A seventh clade is found at the base of C4 Cyperus and is not a true Lipocarpha species. Phylogeny as well as ontogeny confirm this. For Ascolepis it is necessary that new primers and/or markers will be tested, since the method used now seems not successful.
Stacks Image 155
Relevant publications:
Larridon I, Govaerts R, Bauters K, Goetghebeur P (accepted) Cyperus albescens, a new combination in Cyperus (Cyperaceae) for the common (sub)tropical African and Asian species Lipocarpha chinensis. Kew Bulletin.
Bauters K
, Larridon I, Reynders M, Asselman P, Vrijdaghs A, Muasya AM, Goetghebeur P. (2014) A new classification for Lipocarpha and Volkiella as infrageneric taxa of Cyperus s.l. (Cypereae, Cyperoideae, Cyperaceae): insights from species tree reconstruction supplemented with morphological and floral developmental data. Phytotaxa 166 (1): 1-32.
Bauters K. (2011) Molecular Phylogeny and Systematics of Ascolepis, Lipocarpha and Volkiella (Cyperaceae). MSc thesis, Ghent University, Belgium.

Researcher:
Drs. Kenneth Bauters

Laboratory technicians:
Pieter Asselman

Supervisors:
Prof. Dr. Paul Goetghebeur
Prof. Dr. Isabel Larridon

Collaboration:
Prof. Dr. A. Muthama Muasya - University of Cape Town, South Africa
Dr. Alexander Vrijdaghs - KULEUVEN, Belgium

Funding:
Ghent University
Department of Biology
Research Group Spermatophytes
Ghent University Botanical Garden