Botanic Gardens Trust, Sydney, Australia

Cyperaceae

Karen Wilson Senior Research Scientist, Adjunct Assoc. Professor (UNE)

The family Cyperaceae is a large cosmopolitan family of 90 genera and 4000 species worldwide, with 50 genera and 650 species (many endemic) in Australia. They are commonly called ‘sedges’.

Schoenus

One of the larger genera is Schoenus, with about 120 species. A few species are spread widely around the world, but the greatest diversity by far is in Australia (about 80 species), particularly in the heathlands of the south-west and south-east of the continent. However, the genus has other species all over Australia, in habitats ranging from tropical to arid and alpine. There is a secondary area of diversity in Malesia (13 species, mostly in higher altitude areas).

Karen Wilson has had a long-standing interest in the genus and has described several new species, including one in the Blue Mountains, Schoenus evansianus, which she named after Mr Obed Evans who had a long career in Botany at the University of Sydney and subsequently was honorary curator of Cyperaceae and other monocots at the National Herbarium of NSW. She did a preliminary survey in the 1990s, funded by ABRS, establishing the value of anatomical characters in distinguishing taxa.

Associate Professor Jeremy Bruhl (University of New England), Mrs Wilson and an ABRS-funded postdoctoral fellow, Dr Adele Gibbs, are examining generic and specific limits in the genus using molecular, morphological, developmental and anatomical methods. Initial results from molecular studies suggest that there are several distinct clades in what has been known as Schoenus. The 'Schoenus team' has been joined by a PhD student at University of New England, Mr Paul Mutuku Musili, who is investigating one major clade in more detail. Mr Russell Barrett (Kings Park and Botanic Garden, Perth) is also contributing molecular data.

This study fits within a broader project involving other cyperologists in South Africa and England, examining the phylogeny of the tribe Schoeneae, which is mainly Gondwanan in distribution but with some taxa extending to northern regions. Preliminary results were presented at the Monocots IV conference held in Copenhagen in August 2008. Further results were aired at the International Botanical Congress in Melbourne in July 2011.

Photosythetic pathways

Grasses (family Poaceae) and sedges are the only two monocot families that include species using the C4 photosynthetic pathway. There are also 16 ‘dicot’ families with C4 species, making this an uncommon condition amongst flowering plants that has evolved multiple times. There are several variants of the C4 pathway occuring in sedges, making the family of particular interest in investigating the evolution of this pathway in flowering plants. Over 500 sedge species in 11 genera use the C4 pathway, with another nine species of Eleocharis being variable or intermediate in their pathways. Some of the most important weedy sedges are C4, such as Cyperus rotundus (Nutgrass).

Typically, the C4 species live in warmer regions, where there is high light, high temperature and good availability of water. These C4 species tend to be cold-sensitive but tolerant of salinity and low nitrogen levels. It is suggested that these species offer an attractive model to investigate the functional significance of C4 photosynthesis in terms of nitrogen-use efficiency, as well as in terms of the traditional, but seemingly inappropriate, hypothesis which relates C4 photosynthesis to water-use efficiency.

Assoc. Prof. Jeremy Bruhl (UNE) and Karen Wilson combined the results of their individual and joint research into the photosynthetic pathways found in all genera of the sedges, plus previously published records, in a major reference paper listing over 3000 observations:  J.J. Bruhl and K.L. Wilson (2007) Towards a comprehensive survey of C3 and C4 photosynthetic pathways in Cyperaceae. Pp. 99-148 in J.T. Columbus et al. (eds.), Monocots: comparative biology and evolution. Published as Aliso 23: 99-148. (Rancho Santa Ana Botanic Garden: Claremont).

 

 

Schoenus-species
Schoenus species are among the many sedges that grow in the heaths on the Blue Mountains. Photos: Karen Wilson

haustorium
Even small Schoenus species
supply food to Western Australia's parasitic, yellow-flowered Christmas Tree Nuytsia floribunda. The whitish ball on the Schoenus root is the haustorium through which the Nuytsia draws nutrients.

Cyperus vorsteri
Cyperus vorsteri, a South African C4 species that is becoming a weed in coastal Sydney.

Cyperus cross section
Cross-section of a leaf of Cyperus gunnii, showing the Metcalfe-A variant of C4 anatomy.

Cyperus vorsteri environment
Typical environment for Cyperus vorsteri.