A morphological study of Ptilimnium

The genusPtilimnium, a native of the southeastern states, is composed of five species. Two of these were previously placed inHarperella because the plants bore phyllodes instead of finely dissected compound leaves. Investigation shows that these “Harperella” species,P. nodosum andP. fluviatile, have a haploid chromosome number of 6.P. capillaceum, P. nuttallii, andP. costatum have haploid numbers of 7, 7, and 16, respectively. Seedling studies support the thesis that these five species belong to the same genus.P. fluviatile andP. viviparum have been combined because of the lack of distinguishing characters. Connecting links have been discovered between the seemingly isolated localities in the Potomac River valley and northern Alabama.P. texense, a taxon of possible hybrid origin, needs further cytological clarification.