A Phylogenetic Checklist of Sorbus S.L. (Rosaceae) in Europe
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Memoranda Soc. Fauna Flora Fennica 93: 1–78. 2017 ISSN 0373-6873 (print) Helsinki 13 June 2017 ISSN 1796-9816 (online) A phylogenetic checklist of Sorbus s.l. (Rosaceae) in Europe Alexander N. Sennikov* & Arto Kurtto Sennikov, A., Botanical Museum, Finnish Museum of Natural History, P. O. Box 7, FI–00014 University of Helsinki, Finland. Komarov Botanical Institute of Russian Academy of Sciences, Prof. Popov Str. 2, RU–197376 St Petersburg, Russia.*e-mail: [email protected] (author for correspondence). Kurtto, A., Botanical Museum, Finnish Museum of Natural History, P. O. Box 7, FI–00014 University of Helsinki, Finland. A new checklist of Sorbus s.l. in Europe provides an updated classification of this group accord- ing to the latest phylogenetic studies. In order to achieve monophyly, five non-hybrid genera are accepted which represent separate evolutionary lineages (Aria, Chamaemespilus, Cormus, Sorbus s. str., Torminalis), with five hybridogenous genera described here (Borkhausenia = Aria × Sorbus × Torminalis, Hedlundia = Aria × Sorbus, Karpatiosorbus = Aria × Torminalis, Majovskya = Aria × Chamaemespilus, Normeyera = Aria × Chamaemespilus × Sorbus). The checklist includes 201 taxa accepted at the species level: 5 diploid species, 5 diploid hybrids, 186 apomictic species, and 5 apomictic hybrids. Numerous new binomial combinations are proposed to reflect the phyloge- netic position of accepted taxa. The synonymy and nomenclature are revised, and lectotypes are designated for ten plant names. In addition, a new nothogeneric name, Sorbomeles, is proposed for hybrids between Sorbus and Micromeles. Additional key words: apomictic taxa, hybridogenous taxa, hybrids, Mountain-ash, new names, nomenclature, phylogeny, Rowans, Service Tree, synonymy, taxonomy, typification, Whitebeams Introduction & Dickinson 1990; Vamosi & Dickinson 2006). Polyploidy and apomixis lead to a higher taxo- Atlas Florae Europaeae (AFE) is not only a nomic diversity (increased species richness), and large-scale project for mapping vascular plants the groups that are particularly species-rich re- in Europe. While its original purpose, to serve ceived a special attention in AFE: Alchemilla L. as a complement to Flora Europaea (Tutin et al. (Kurtto et al. 2007) and Rubus L. (Kurtto et al. 1964–1980), has been surpassed long ago, AFE 2010). The third genus of Rosaceae with extraor- provides updated taxonomic synopses for the dinary taxonomic difficulties to be mapped in Eu- purposes of data collection and mapping and also rope is Sorbus L. s.l. contributes its taxonomy to larger taxonomic da- The taxonomic diversity of Sorbus in Europe tabases like Euro+Med PlantBase (Kurtto 2009). is currently being accommodated within a single, The mapping of Rosaceae has been proven traditionally defined genus, although evidence particularly difficult because of the widespread has been increasingly growing that Sorbus s.l. in- occurrence of polyploidy which is often associ- cludes five main evolutionary lineages and in the ated with gametophytic apomixis (e.g. Campbell current circumscription it is apparently polyphy- 2 Sennikov & Kurtto • Memoranda Soc. Fauna Flora Fennica 93, 2017 letic (Campbell et al. 2007). Besides these main Medicus (1789) restricted the genus Sorbus to lineages, intermediate taxa of hybrid origin are a single species, S. domestica, and his choice was not uncommon; these should also be classified sometimes followed and reflected in the earliest correctly in the phylogenetic taxonomy. typification of the name (Pfeiffer 1874; Green in The main purpose of the present contribution Hitchcock & Green 1929). However, most of re- is to summarise the knowledge on the taxonomy, searchers wished to restrict the genus to S. aucu- distribution, synonymy and nomenclature of Sor- paria and its relatives, and this treatment was for- bus s.l. in Europe, augmenting and improving the malised in the second generic typification (Reh- provisional checklist published by Kurtto (2009). der 1949) and a conservation proposal (Brizicky Another purpose is to update the formal taxonom- 1968; Kovanda & Pouzar 1982; Sennikov 2014), ic classification of this group as to reflect the phy- and finally the generic type was recommended for logenetic relationships and to achieve monophyl- conservation by the Nomenclature Committee for etic taxa. The resulting checklist provides a taxo- Vascular Plants (Applequist 2016). nomic backbone for the ongoing mapping of the The last generic segregate was separated by group in Atlas Florae Europaeae. Host (1831) who erected the genus Aria (Pers.) Host on the basis of the subgenus established by Persoon (1806), into which he placed three spe- History of studies at the genus level cies with subentire leaves (including S. chamae- mespilus and its hybrid S. hostii). This genus was The genus Sorbus, when validly published by Lin- later restricted according to its type, with many naeus (1753), included only two species (S. aucu- relatives added (Roemer 1847). The monograph paria, S. domestica) which were distinguished as of Roemer (1847) was probably the last author- a genus of its own because of three styles (the itative work of classical times in which narrow character of S. aucuparia only, because S. domes- generic segregates of Sorbus s.l. were accepted. tica is characterized by five styles) and also pin- Persoon (1806) already collected nearly all nate leaves. The name and circumscription of the the Linnaean members of Sorbus s.l. into a sin- genus were borrowed from Tournefort (1719). gle genus, except for S. chamaemespilus which Other species of Sorbus s.l. known to Linnaeus was placed into Aronia on the basis of five styles were classified into other genera: Crataegus L. (the presence of five styles in S. domestica still (Crataegus aria = Sorbus aria, Crataegus torm- was neglected, and that species was treated as tri- inalis = Sorbus torminalis) with two styles (and stylous also by Persoon). The collective concept non-pinnate leaves), Mespilus L. (M. chamae- of Sorbus became dominating by the end of 19th mespilus = S. chamaemespilus) with five styles century. But even the broader Pyrus L., embrac- (and subentire leaves). These species, which sub- ing the whole of Malinae, was preferred by some sequently formed separate genera, were classified other authors (e.g. Candolle 1825). by Linnaeus primarily on the basis of number of It was only recently that the narrow gener- styles, the character potentially useful in formal ic segregates of Sorbus s.l. enjoyed acceptance classifications but of limited evolutionary signif- again, firstly on the grounds of morphology (Rob- icance. ertson et al. 1991) and then molecular phylogeny Other (”natural”) characters in the structure of (see below). These narrowly defined genera are fruits were observed after Linnaeus. Most nota- still accepted almost exclusively in phylogenet- ble were works of Medicus who revolutionarily ic works, whereas taxonomic synopses have been revised the generic taxonomy of many groups in- reluctant to accept splitting because early phy- cluding the Rosaceae with apple-like fruits. Medi- logenies were not well resolved (e.g. Rich et al. cus (1789) established the genera Chamaemespi- 2010). lus Medik. (fruit closed, not fleshy), Aucuparia Although the main taxonomic groups of Sor- Medik. (fruit open, similar to Sorbus = S. domes- bus s.l. were established early and had been con- tica), and Torminalis Medik. (fruit closed, fleshy), stantly recognized at least at the level of subge- of which Aucuparia was validly published later nus, intermediate (hybridogenous) taxa were (Medicus 1793). most frequently left unclassified to an infragener- Memoranda Soc. Fauna Flora Fennica 93, 2017 • Sennikov & Kurtto 3 ic category. It was rather recently when these hy- lus having arisen from the crosses between Aria bridogenous groups were named at the level of and Torminalis. subgenus (Májovský & Bernátová 2001; Rich et In the latest phylogenetic studies (Lo & al. 2014). At the level of genus these groups were Donoghue 2012) the summary tree produced named in Mezhensky et al. (2012). from combined plastid data demonstrated a 70– 77% level of bootstrap support for the members of the clade including Sorbus s.str., Cormus and Pyrus s.str., whereas Aria s. str. (included for the General notes on phylogeny first time in phylogenetic analyses) was found in another clade with Aronia. The combined chloro- Phipps et al. (1990) and Robertson et al. (1991) in plast and nuclear ITS-based phylogenetic tree in their comprehensive generic revision of Maloide- the same work demonstrated (in spite of the low ae (now Malinae) disassembled Sorbus s.l. into level of support) the sister position of Torminal- five smaller genera (Aria, Chamaemespilus, Cor- is, Aria s.str. and Chamaemespilus, on one side, mus, Sorbus, Torminalis) on the basis of morpho- and Pyrus s.str., Cormus and Sorbus s.str., on the logical differences in habit, leaves, inflorescenc- other side, with both branches being situated re- es, flowers, and fruits. They noted the extensive motely on the tree. Judging from these data, split- intergeneric hybridization which affects 24 of 28 ting of Sorbus s.l. into at least two groups is in- genera, which they recognised (including 4 of 5 evitable, one with simple leaves and the other genera of Sorbus s.l.), and ”seems to reflect weak with pinnate leaves. However, the phylogenet- overall barriers to hybridization rather than indi- ic proximity of members of those groups would cate evolutionary