A Question about the Names of R. nudiflorum and R. roseum
Lloyd H. Shinners
Southern Methodist University, Dallas Texas
Reprinted from Castanea 27:94-95, 1962
Fig. 40. R. nudiflorum
Rhododendron nudiflorum and R. roseum (Ericaceae) : illegitimate names. - "The Azaleas of North America," by Alfred Rehder (forming the second portion of "A Monograph of Azalea," Rhododendron Subgenus Anthodendron, by Ernest Henry Wilson and Alfred Rehder; Publ. Arnold Arboretum No. 9, 1921), is the last and really only thorough revision of the group. But the nomenclatural rules followed by Rehder differed somewhat from those now in force, so that two widespread species cannot retain the names under which they appear in Rehder's account.
Azalea nudifiora L., Sp. Pl. ed. 2, l: 214, 1762, was technically a substitute name for A. lutea L,. Sp. Pl. ed 1, 1: 150, 1753, The latter was based on a mixture of no less than three species: A. nudiflora, A. canescens, and A. calendulacea. On the basis of specimens from Kalm, Linnaeus both renamed and emended the species, giving prominence to the A. nudiflora element (as later understood), but failed to drop the discordant synonyms referring to the others. Michaux in 1803 ignored the confused Linnaean treatment, describing all three elements as new and distinct species. Pursh subsequently placed A. nudiflora in synonymy under A. periclymenoides Michx, thus definitely typifying it by that element in the mixture which later authors have treated as A. nudifiora. (These points were discussed long ago by S. F. Blake: "Notes on the Clayton Herbarium 8. Azalea lutea L.," Rhodora 20: 53-54, 1918,) Under present rules, the binomial Azalea nudiflora L. is illegitimate, since it included the type of the previously and validly published A. lutea L., which name ought to have been retained. As it happens, the latter cannot be transferred to Rhododendron because of the validly published R. luteum Sweet, 1830. The combination R. nudiflorum (L.) Torr. could only be retained if there were no other legitimate epithet available. But Azalea periclymenoides Michx., Fl. Bor. - Am. 1: 151, 1803 is available and not already used under Rhododendron, so that R. periclymenoides (Michx.) Shinners, comb. nov. must replace the binomial R. nudiflorum of current manuals. Those who retain the segregate genus Azalea must call the plant, quite inappropriately, Azalea lutea L, (The name Azalea lutea of recent popular works on azaleas represents an illegitimate transfer of Rhododendron luteum Sweet, mentioned above, and refers to an Asiatic species.) In Rehder's account the name R. venustum Salisb., Prodr. p. 287, 1796, is listed as synonym of R. nudiflorum "in part." This was published by Salisbury as a new name for both Azalea nudiflora and A. viscosa of Linnaeus, which he did not consider distinct. R. venustum is of course illegitimate since an available earlier epithet was give in synonymy but not adopted. In Index Kewensis Salisbury's name is stated to be a synonym of the Asiatic R. arboreum, which interpretation I can only explain by assuming that Salisbury in reality saw plants of two forms of R. arboreum misidentified as Azalea nudiflora and A. viscosa, and that the editors of Index Kewensis knew of this. As published, however, R. venustum was explicitly a nomen novum for the two Linnaean species from America, and being illegitimate, cannot be adopted so long as a legitimate epithet is available.
Quite similar to the preceding is the case of Rhododendron roseum Loisel. Rehder, based on Azalea rosea Loiseleur in Duhamel, Traite Arb. Arbust. ed. 2, 5: 224, 1812. Since Loiseleur cited as synonym the earlier A. canescens Michx. (according to Rehder, p. 141; I have not seen the Duhamel reference), his binomial is automatically illegitimate, even though he happened to illustrate a different species in publishing it. Since his broad interpretation included the type of A. canescens Michx. as well, his name must be rejected. The species then is correctly known as either Azalea prinophylla Small, N. Amer. Fl. 29: 42, 1914, or better as Rhododendron prinophyllum (Small) Millais, "Rhododendrons" p. 229, 1917. The New Britton & Brown and the 8th edition of "Gray's Manual" give Missouri as the southwestern limit of this species." Small's Manual" correctly credits it to Arkansas. On the basis of specimens in the SMU Herbarium, it can be reported that it occurs not only widely in Arkansas (Cleburne, Garland, Hot Spring, Montgomery, Newton, Polk, and Stone counties), but extends slightly into eastern Oklahoma (Le Flore Co.: 15 miles east of Muse, 4.5 miles west of Oklahoma-Arkansas state line, G. Thomas Bobbins 2985).
I wish to express my thanks to Lazella Schwarten, Librarian, Harvard University Herbaria, who kindly supplied me with a copy of Salisbury's original publication of Rhododendron venustum.