New nomenclature combinations in the green alder species complex (Betulaceae)

Abstract The name Alnus viridis (Chaix) DC., based on Betula viridis Chaix (1785), has traditionally been attributed to green alders although it is based on a later basionym. Alnus alnobetula (Ehrh.) K. Koch based on Betula alnobetula Ehrh. (1783) is the correct name for green alders. In light of the increasing use and recognition of the name Alnus alnobetula (Ehrh.) K. Koch in the literature. I herein propose new nomenclatural combinations to account for the Japanese and Chinese subspecies respectively: Alnus alnobetula subsp. maximowiczii (Callier ex C.K. Schneid.) J. Chery and Alnus alnobetula subsp. mandschurica (Callier ex C.K. Schneid.) J. Chery. Recent phylogenetic analyses place these two taxa in the green alder species complex, suggesting that they should be treated as infraspecific taxa under the polymorphic Alnus alnobetula.


Introduction
Characteristic to the genus, Alnus alnobetula (Ehrh.) K. Koch is an anemophilous shrub with carpellate catkins that develop into woody strobili. It has a circumpolar distribution with subspecies in Europe (Greuter andRaab-Straube 2011, Flora Euro-pea [http://rbg-web2.rbge.org.uk/FE/fe.html -accessed 22.07.2015], North America (Furlow 1979, Furlow 1990, Fl. North. Amer. North of Mexico Editorial Committee 1997, and Asia (Löve 1968, Li and Skvortsov 1999, Ohba 2006. A phylogeny using nuclear ribosomal DNA ITS sequences generated a polytomy containing fi ve taxa within the green alder species complex due to low sequence divergence among the individuals (Chen and Li 2004). Ren et al. (2010) found the green alder species complex to be a monophyletic clade with the unique character state of a thymine at position 192 of the ITS region. Banaev and Adel'shin (2009) also found close affi nity of green alder species using molecular data.
Th e name Alnus viridis (Chaix) DC. has long been attributed to green alders; however a closer look at the literature reveals the name Alnus alnobetula (Ehrh.) K. Koch has priority (Pouzar 1982, Holub 1986 (Lambinon and Kerguélen 1988). Subspecies names for the Japanese green alder and Chinese green alder are assigned here.

Nomenclature history
Th e confusion lies in the appropriate basionym of this taxon. Th e name Betula viridis Chaix dates from 1785 (unable to access original text; revisited in Perret and Burdet 1981). No type specimen was designated. Two years earlier, Betula alnobetula Ehrh. was published by Ehrhart (in Gartenkalender 1783) describing a shrub in which "the homeland is unknown to me" (translated from German). In Ehrhart (1788), he republished his work where the name Betula alnobetula Ehrh. reappeared.
As Betula species were transferred to Alnus, authors were evidently unaware of the original 1783 publication of the name B. alnobetula Ehrh., so B. viridis Chaix was thought to be the older name and was taken to be the basionym for green alders. Alnus alnobetula Ehrh. has consistently been associated with the 1788 reproduced work and thus listed as a later synonym of A. viridis (Chaix) DC.
Major databases such as plantlist.

Conclusions
Th e close relatedness of the green alder species complex members is supported by recent phylogenetic anaylses. Th e use of a single nrDNA marker, ITS, generated a weakly supported clade of A. mandshurica, A. fi rma, A. pendula and A. sieboldiana embedded within a greater polytomy that includes all other green alders (see strict consensus parsimony tree by Chen and Li 2004). In more recent phylogenetic analysis, A. maximowiczii and A. mandshurica always form a monophyletic clade with the rest of the green alders (Ren et al. 2010, Banaev andAdel'shin 2009). Given this evidence, it is appropriate to change the rank of these taxa to subspecies of the green alders. Th e proposed nomenclature changes utilize the correct species epithet and recognize their phylogenetic placement as lineages of a polymorphic Alnus alnobetula.
Infraspecifi c rankings of plants, specifi cally subspecies and variety, have been used rather interchangeably (Hamilton and Reichard 1992). Th e green alder species complex has historically been separated into subspecies due to geographic and morphological distinctiveness. I here agree with this subspecies concept and propose two new nomenclatural combinations to account for the Japanese and Chinese green alder subspecies. Th is change provides the proper nomenclature for future taxonomic and phylogenetic studies in the green alder species complex.