Phylogenetic Relationships within the Rhodoreae (Ericaceae) with Specific Comments on the Placement of Ledum

Abstract

The cladistic relationships of the tribe Rhodoreae (Ericaceae; Rhododendroideae) are investigated. The tribe is likely monophyletic, and may be diagnosed by the perulae found with the inflorescence. The genus Rhododendron, as currently recognized, is shown to be paraphyletic. However, if Ledum is included (as a subsection of sect. Rhododendron, within subg. Rhododendron), and Therorhodion is excluded, then the genus is probably monophyletic. Ledum likely is related most closely to Rhododendron subsect. Edgeworthia. The cladistic relationships within Rhododendron are consistent with the recognition of eight subgenera: Anthodendron, Azaleastrum, Candidastrum, Chonias- trum, Hymenanthes, Mumeazalea, Rhododendron, and Tsutsusi. The monophyly of Copeland's segregate genera is thus, in large part, supported, although these groups are placed here at subgeneric rank. Among these subgenera, Anthodendron is possibly cladistically basal. This subgenus and the phe- netically similar subgenera Tsutsusi, Azaleastrum, Choniastrum, Candidastrum, and Mumeazalea have been recognized traditionally as the azalea complex or chorus subgenerum Nomazalea, but this group is paraphyletic and should not be given formal taxonomic recognition. The circumscription and phylogenetic relationships of some subgenera, e.g., Azaleastrum (as broadly defined, i.e., in- cluding Choniastrum, Mumeazalea, and Canadidastrum) need further study. Menziesia and Tsusiophyllum are recognizable at the generic level, and may be related due to the shared possession of slit-like anther dehiscence. Thus, the pattern of character variation within the tribe may be expressed bv the recognition of four genera: Therorhodioni, Menziesia, Tsusiophyllurn, and Rhododendronq The fol- lowing new combinations are made: Rhododendron subsect. Ledum, R. palustre, R. groenlandi cum.