Evolution of Cyperaceae

Karen Wilson, Acting Manager Plant Diversity

The family Cyperaceae is a big cosmopolitan family of 90 genera and 4000 species worldwide, with 50 genera and 650 species (many endemic) in Australia. They are commonly called ‘sedges’. Karen Wilson has studied the classification and phylogeny of sedges for most of her career, working on a range of projects both individually and jointly with other cyperologists and students. This year several projects have come to fruition; notably with publications on the tribe Abildgaardieae, on the molecular phylogeny of the family, and on photosynthetic pathways in the family.

Assoc. Prof. Jeremy Bruhl (UNE) and Karen Wilson compiled the results of their individual and joint research into the photosynthetic pathways found in all genera of the sedges, plus previously published records, to produce a major reference paper* listing over 3000 observations.

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.

* 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).

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

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

Typical environment for Cyperus vorsteri.