SCLERIA: Biodiversity & Evolution

October 2011 to present, PhD study & MSc thesis

The genus Scleria, commonly known as nut rushes or razor grasses, is, with its ca. 250 species, one of the major genera in the sedge family (Cyperaceae). In this family, the genus is placed in the monotypic tribe Sclerieae. The genus has a pantropical distribution and can occasionally be found in (warm) temperate regions. Recognition and description of infrageneric taxa has always been a controversial taxonomic activity. All known infrageneric classifications have been the result of personal interpretations without molecular evidence.

In Camelbeke (2002), eight types of inflorescence are recognized. The basic type of inflorescence seems to be a panicle and all other inflorescence types in Scleria are most likely derived forms of this paniculate type. We also find four different types of spikelets: truly bisexual spikelets (androgynous spikelets), subandrogynous spikelets (functionally unisexual spikelets with a conspicuous rachilla with more or less well developed glumes above the glume subtending single female flower), many-flowered staminate spikelets and pistillate spikelets. It is thought that the true bisexual spikelets represent the ancestral state while the subandrogynous spikelets are intermediate between the strictly unisexual ones. This hypothesis is only based on morphological observations and an evolutionary context would be appropriate to confirm this.
At the base of the Scleria nutlet, a specialized structure is found, namely the hypogynium. The identity of this structure is still unknown and it seems impossible to determine its identity (homology) without combining morphological, ontogenetic and molecular data. This hypogynium is supported by an outer lower structure, a cupule, which like the hypogynium, generally develops into a more or less 3-lobed organ, with the lobes of the hypogynium and cupule always opposite (Camelbeke, 2002). Just like the hypogynium, the identity of the cupule is unknown.

There are a number of aims/goals for this study. First a phylogenetic hypothesis of the genus Scleria and its close relatives (Bisboeckelereae) will be constructed. Outgroups will be carefully chosen based on previous studies. With the help of the obtained phylogenetic hypothesis, we can construct an infrageneric classification paying attention to the previously described sections. We will test the monophyly of these sections and in extension the monophyly of the whole genus.

Some of the evolutionary hypotheses to be tested are:
- Scleria is a monophyletic genus.
- There are different synapomorphies which delimitate the different sections.
- The different inflorescence types are all derived from the basic paniculate type.
- True bisexual spikelets are ancestral while the subandrogynous spikelets are intermediate between the bisexual and the strictly unisexual spikelets.
- The close affinities with the Bisboecklereae
- The phylogeography of the genus Scleria

An important part of this study is the revision of the taxonomy in the genus Scleria. All available species will be studied and their taxonomy will be cleaned up extensively. “Is a species really a species?” is one of the major questions here. We aim to clearly estimate the species number and to delimitate the species boundaries. Together with the obtained phylogenetic hypothesis, we will present an infrageneric classification for the whole genus.

Another aim is to resolve the mystery around the cupula and the hypogynium. What are these structures? Are they newly evolved (de novo) structures? Or are they modified perianth parts? Are there affinities with Bisboeckelereae?

As a final part of this study we aim to construct an identification key for the different sections and the whole genus. Since no identification key for the whole genus is made yet, this could be very useful for future studies of Scleria.
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Relevant publications:
Bauters K, Asselman P, Simpson DA, Muasya AM, Goetghebeur P, Larridon I (2016) Phylogenetics, ancestral state reconstruction, and a new infrageneric classification of Scleria (Cyperaceae) based on three DNA regions. Taxon 65 (3): 444-466.
Bauters K, Meganck K, Vollesen K, Goetghebeur P, Larridon I. (2015) Scleria pantadenia and Scleria tricristata: Two spectacular new Scleria subgenus Hypoporum species (Cyperaceae, Cyperoideae, Sclerioideae) from Tanzania. Phytotaxa 227(1): 45-54.

Researcher:
Drs. Kenneth Bauters

MSc students involved:
Kenny Meganck

Laboratory technicians:
Pieter Asselman
Viki Vandomme

Supervisors:
Prof. Dr. Paul Goetghebeur
Prof. Dr. A. Muthama Muasya - University of Cape Town, South Africa

Doctoral advisory committee:
Prof. Dr. Isabel Larridon
Prof. Dr. David A. Simpson - Royal Botanic Gardens, Kew, UK
Dr. Alexander Vrijdaghs - KULEUVEN, Belgium

Funding:
Research Foundation Flanders international mobility grants (USA, Zambia)

King Léopold III Foundation for the Exploration and Protection of Nature (international mobility - USA, Zambia)

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