A revision of the infraspecific taxonomy of Cyperus esculentus (yellow nutsedge) with an experimentally evaluated character set

Cyperus esculentus (Yellow Nutsedge) is a troublesome weed with broad infraspecific variation. A growing experiment was performed in which diverse clones were raised under different environmental conditions. Sixty five characters were measured and evaluated based upon their sensitivity to environmental and clonal differences. Of these, 17 proved to be sufficiently reliable for taxonomic purposes. They concern size and shape of floral parts rather than dimensions of spikes, which were until now thought to be the diagnostic characters. Herbarium material from all continents where C. esculentus is present was studied, including type material of varieties; 70 plants were selected, the 17 parameters measured, and the data analysed by multivariate techniques. Four clusters were distinguished, which appeared to broadly represent four varieties described by Kii- kenthal in 1935; three of his seven varieties were rejected, var. cyclolepis, var. nervoso-striatus, and var. sprucei. The four remaining varieties are discussed and described, and a key is given for their identification. They are var. esculentus, var. leptostachyus, var. macrostachyus, and var. heermannii. All of these varieties occur in the Americas as well as in Europe. Variety esculentus dominates in Africa and southern Europe, var. leptostachyus is rather common in both the Old and the New World. Two varieties, var. macrostachyus and var. heermannii, have been recently introduced into the Netherlands; they probably originate from the Americas. The occurrence of var. leptostachyus in Europe is probably the result of an earlier introduction.