Phylogenetic distribution of dauciform roots in North American sedges (Carex, Cyperaceae)

Specialized carrot-shaped roots, termed dauciform roots, were first described from a few European sedges (Cyperaceae) in 1966, and have subsequently been shown to occur in some Australian sedge genera.  Experimental studies in Australia have confirmed their role in facilitating phosphorous uptake and demonstrated that they can be induced under low phosphorous conditions. In this first report of dauciform roots on sedges in North America, we illustrate the morphology of these specialized roots in Carex and demonstrate phylogenetic differences in induction of these roots under low P conditions. We compared 62 species of Carex in a greenhouse experiment with three replicates of complete and low P nutrient treatments.  Species were chosen to represent the three subgenera of Carex in North America and to assess consistency of dauciform root induction within clades of subgenus Carex.  None of the five tested species of subgenus Vignea formed dauciform roots under complete or low P treatments.  In contrast, dauciform roots were induced on 80% of the 55 tested species of subgenus Carex and both tested species of subgenus Psyllophora in the low P treatment.  Only 8% of these species also formed a few dauciform roots in the complete nutrient treatment. Within subgenus Carex, dauciform roots were induced in all tested species of 12 clades, including species in sections Acrocystis, Bicolores, Ceratocystis, Careyanae, Griseae, Hymenochlaenae, Lupulinae, Laxiflorae, Paniceae, but were induced only rarely or not at all in section Phacocystis.  In contrast to the clear phylogenetic pattern, there was no apparent relationship to habitat type.