Phylogeny inferences of Cyperus esculentus L. (Cyperaceae) based on chloroplast sequence data.

Cyperus esculentus L. belongs to Cyperaceae, a family comprising about 109 genera and 5500 species, with Cyperus comprising about 686 species (Muasya et al., 2009). Cyperus esculentus is a perennial weed herb, easily spreading by means of seeds and tubers (in wild races), often cultivated. As a consequence, C. esculentus has a wide distribution and although prefers warm areas, it is enlarging its range into cooler climates. Cyperus esculentus is a C4 plant and an obligate outcrosser. It is subdivided in the varieties esculentus, leptostachyus Boeck., macrostachyus Boeck., and hermannii (Buckley) Britton; in addition, the tubers of var. sativus Boeck. are worldwide used for their properties as food and medicine (Holm et al., 1977). The origin and distribution of C. esculentus have been studied from a morphological point of view (Ter Borg & Schippers, 1992; Ter Borg et al., 1998), but never using molecular methods. The objective of this work is to study C. esculentus by molecular methods in order to improve the knowledge of the evolutionary history of the species and its varieties. The sequencing of chloroplast markers of about 80 C. esculentus accessions from different areas of the world and of other Cyperus species as reported in Muasya et al. (2002) has been analysed. The chosen regions include the gene rbcL and an intron (rps16), selected as potentially useful according to previous reports on Cyperus phylogeny (Muasya et al., 2002; Simpson et al., 2007). Sequence identity within C. esculentus accessions resulted to be 100% for the rbcL and 98% for the rps16 that showed four haplotypes: X for American (F = 55%) accessions, Y for European (F = 15%), American (F = 10%) and African accessions (F = 5%), W for European and African accessions (F = 10%), Z for American (F = 5%) accessions. The phylogenetic analysis was carried out by using the PAUP* 4.0b10 software (Swofford, 1998), under a framework of maximum parsimony (MP). The MP analysis of the combined matrix (rbcL gene and rps16intron) yielded ten MP trees (CI = 0.778; RI = 0.76); the length consensus of the MP trees was 474 steps. According to these data, C. esculentus results divided into two clades. The relationships among plastid DNA haplotypes of C. esculentus accessions were analysed through a haplotype network, constructed with TCS software (Clement et al., 2000). The present analysis seems to show that the ancestral haplotype originated in America (i.e, X). Such a hypothesis could be confirmed by our further investigations by using nuclear molecular markers as ETS1f and/or ITS1 that showed to be very useful in these kinds of analysis (Larridon et al., 2011; De Castro, data unpublished).