NOMENCLATURE HISTORICAL 5 



except that in one or two cases notably that of the plant usually known 

 as P. lati folium the American principle ''once a synonym always a 

 synonym" has led to the adoption of a specific name of more recent 

 origin than that first used when the latter, under Viscum, was preoccu- 

 pied, even though it does not appear elsewhere under Phoradendron; 

 and in two or three instances e. g. what is here called P. Engelmanni 

 a new specific name has been preferred even though an existing or lapsed 

 varietal name might have been used in a specific sense. An embarrassing 

 difficulty is introduced through Professor Urban 's otherwise unimpeach- 

 able publications in the latinization of the customary Greek generic 

 name Phoradendron into Phoradendrum, which compels a monographer 

 to choose between recombining the names of all of Urban 's species under 

 the former or recombining the still larger number of earlier and classic 

 names under the emended generic name. I have felt that of the two 

 regrettable courses the former is preferable; and customary practice 

 retains numerous other generic names with the Greek ending. 



HISTORICAL SUMMARY 



The exclusively American genus Phoradendron was differentiated in 

 1847 from its Old World equivalent, Viscum, by Nuttall, its essential 

 characters being trimerous flowers in simple spikes, with contiguous 

 fruiting sepals, as contrasted with tetramerous solitary or simply cymose 

 flowers and distinctly separate sepals in Viscum. Almost simultaneously 

 with Nuttall, Engelmann recognized the generic separability of these 

 New- and Old-world mistletoes, and segregated the latter under the 

 name Spiciviscum. Before his description was printed in 1849, however, 

 Nuttall's paper had appeared, so that Dr. Gray, to whom Engelmann ' 

 manuscript had been sent, though publishing the name Spiciviscum 

 treated it as a synonym of Phoradendron, and only one species has ever 

 been seriously named Under Engelmann 's proposed genus. 



Except for a few which Humboldt, Bonpland and Kunth had placed 

 in Loranthus, all of the species now referred to Phoradendron which 

 had been published prior to Nuttall's segregation of the genus had 

 been described as species of Viscum, so that, so far as they antedate the 

 appearance of de Candolle's monograph of Loranthaceae in the Prod- 

 romus, they were brought into position under Viscum in that work. 

 Nuttall himself named a number of these as pertaining to his new genus 

 and indicated clearly that this was probably equally true of most if 

 not all of the American species of Viscum. Apparently unacquainted 

 with the publications of Nuttall and Engelmann, Miers in 1851 sug- 

 gested that the South American species of Viscum, with anthers dehis- 

 cent by slits, were not cogeneric with the European species, the anthers 



