Introduction

The genus Leucanthemum Mill. (marguerites, ox-eye daisies; Compositae, Anthemideae) comprises 42 flowering plant species (Euro+Med 2006+) distributed all over the European continent and represents an attractive system for studying reticulate evolution on the diploid (Oberprieler & al. 2014; Konowalik & al. 2015; Wagner & al. 2017) and polyploid (Oberprieler & al. 2011, 2014; Greiner & al. 2012, 2013) level. While working towards an evolution-based taxonomy of ox-eye daisies throughout their natural distribution range in C and S Europe, we found a new, octoploid chromosome number for populations of a taxon described as L. vulgare [subsp. glaucophyllum] var. esterellense by Briquet & Cavillier (1916) in their treatment of Compositae in Émile Burnat's Flore des Alpes maritimes. This taxon was putatively assigned to L. adustum (W. D. J. Koch) Gremli by Tison & de Foucault (2014). Leucanthemum adustum is a species occurring in the W and E parts of the Alps, from which L. vulgare var. esterellense deviates karyologically (hexaploid vs octoploid), morphologically (leaves somewhat glaucescent, involucral bracts less dark margined) and ecologically (growing on acidic instead of calciferous soils). Accordingly, a clarification of its evolutionary relationships to other co-distributed Leucanthemum species was initiated using karyological, morphological, and molecular sources of evidence. The results of this study are on the way to being published (C. Oberprieler and collaborators, submitted) and support the taxonomic independence of L. vulgare var. esterellense. The present contribution, however, is intended to communicate chromosome numbers of the study group and to draw the necessary nomenclatural consequences.

Material and methods

The present study comprises chromosome counts for the three varieties of Leucanthemum vulgare subsp. glaucophyllum (Briquet & Cavillier 1916) (i.e. L. vulgare var. esterellense, L. vulgare var. glaucophyllum and L. vulgare var. subglaucum), along with the co-distributed L. pallens, with which mixed stands are formed in some regions. Chromosome numbers were obtained from somatic mitoses of root tips of plants collected in the field and cultivated in the Berlin Botanic Garden or raised from seed. Root tips were pre-treated with hydroxyquinoline (0.002 molar aqueous solution) for 2 hours, fixed in 96% ethanol/ glacial acetic acid (3:1) and refrigerated. Hydrolysation was carried out with 1–2N hydrochloric acid for 10–15 minutes at 60°C. For chromosome staining root tips were squashed in aceto-orcein. Chromosome counts were made for several plants of a common seed origin. Five to ten metaphase stages were examined for every plant.

Voucher specimens of the original collections and of plants cultivated in the Berlin Botanic Garden are deposited in B.

Results

Results indicate that the three putative varieties of Leucanthemum vulgare subsp. glaucophyllum exhibit three different ploidy levels: While the typical L. vulgare var. glaucophyllum is characterized by a decaploid chromosome number, L. vulgare var. esterellense was found to be an octoploid, and L. vulgare var. subglaucum to be a hexaploid. In one of the sampled localities (Monte Bignone near Alassio, Italy), where populations of L. pallens (hexaploid) and L. vulgare var. glaucophyllum were found growing in close proximity, individuals with intermediate ploidy levels were found (heptaploids, octoploids).

Discussion

Following the presently provided karyological evidence, we consider it well supported that the three varieties of Leucanthemum vulgare subsp. glaucophyllum constitute three different evolutionary lineages that merit acknowledgement as three independent species. While these taxonomic consequences have been drawn already in the cases of the hexaploid L. vulgare var. subglaucum (through its original description at specific rank as L. subglaucum de Laramb.) and the decaploid L. vulgare var. glaucophyllum (by Jahandiez 1922), raising of the octoploid L. vulgare var. esterellense to specific rank is proposed here.

Additionally, owing to the observation of recently formed hepta- and octoploid hybrids between the hexaploid Leucanthemum pallens and the decaploid L. glaucophyllum in areas of joint occurrence (as in the mixed stand on Monte Bignone studied in the present contribution), we propose the name L. ×marchii for these karyologically and morphologically intermediate plants. This nothospecies epithet acknowledges P. Marchi, who in Marchi & al. (1983) first reported on hybridization between L. pallens and L. glaucophyllum and the occurrence of octoploid hybrid individuals in these stands.

1. Leucanthemum esterellense (Briq. & Cavill.) Vogt, Konowalik & Oberpr., comb. & stat. nov. ≡ Leucanthemum vulgare var. esterellense Briq. & Cavill. in Burnat, Fl. Alpes Marit. 6: 103. 1916 ≡ Leucanthemum glaucophyllum var. esterellense (Briq. & Cavill.) Jahand. in Ann. Soc. Hist. Nat. Toulon 7: 40. 1922. – Ind. loc.: “Massif de l'Esterel^*: Théoule!! au-dessous de la Sainte-Baume!!, aux Suvières! (Saint-Yves) et ravin de Mourrefrey!!”. – Lectotype (designated here): Deuxième voyage botanique de l'année 1899 dans les Alpes maritimes par Emile Burnat et François Cavillier, Vallon de Mourrefrey, entre le Gratadis et la S^te Baume (Esterel), 8 Jun 1899 (G-BU! [G00848001, two-sheet specimen, cf. Turland & al. 2018: Art. 8 Ex. 9]). – Remaining syntypes: Voyage botanique dans les Alpes maritimes de Emile Burnat et François Cavillier, au-dessous de la S^te Baume d'Agay (Esterel), 130–170 m, bords du chemin, silice, 1 Jun 1901 (G-BU! [G00848002]); Théoule, près de Cannes, l'Esterel, Alpes Maritimes, 29 May 1884, É. Burnat (G-BU! [G00848003]); Théoule, au pied de l'Esterel, vallon près du tunel, Alpes Maritimes, 13 Jun 1875, É. Burnat (G-BU! [G00848004, two-sheet specimen]).

Chromosome number — 2n = 72 (octoploid).

Distribution — S France, where the species is endemic to the Massif de l'Esterel and adjacent areas (Briquet & Cavillier 1916).

New chromosome counts

2. Leucanthemum glaucophyllum (Briq. & Cavill.) Jahand. in Ann. Soc. Hist. Nat. Toulon 7: 39. 1922 ≡ Leucanthemum vulgare subsp. glaucophyllum Briq. & Cavill. in Burnat, Fl. Alpes Marit. 6: 102. 1916 ≡ Chrysanthemum leucanthemum var. [“o”] glaucophyllum (Briq. & Cavill.) Fiori, Nouv. Fl. Italia 2: 626. 1927 ≡ Leucanthemum glaucophyllum (Briq. & Cavill.) Marchi & Illuminati ín Ann. Bot. (Roma) 33: 174. 1975, isonym. – Ind. loc.: “Collines, coteaux, rocailles, des régions littorale et montagneuse inférieure, d'Albenga à Agay.“ and “Env. D'Albenga^**: Mont Pisciavino!!, 500 m., mont Bignone!!, 500 m., entre Albenga et Garlenda!!; versant S. du monte Nero!!^** près Zuccarello, 700–800 m.; versant S. du mont Galè!!^**; vallée de l'Arroscia^**: mont Castellano sur Onzo!!, 900–1000 m., mont Sprandega sur Vessalico!!, 750 m., mont Riondo, entre Casanova-Lerrone et Vessalico!!, 500 m.” – Lectotype (designated here): Voyage botanique de MM. Emile Burnat, J. Briquet, Paul Burnat, A. Saint-Yves, Fr. Cavillier, E. Abrezol et J. Lascaud, dans les Alpes maritimes italiennes et françaises (1^er–26 juin 1914), Vallée de l'Arroscia, Mont Castellano sur Onzo, 900–1000 m, rocailles, grès-calcaire, 8 Jun 1914 (G-BU! [G00848005]). – Remaining syntypes: Mont Riondo, entre Casanova-Lerrone et Vessalico (Ligurie occid.), 500 m, grès, 13 Jun 1914, É. Burnat & al. (G-BU! [G00848007]); Mont Sprandega sur Vessalico, Vallée de l'Arroscia, Ligurie occid., 750 m, rocailles herbeuses, grès, 12 Jun 1914, É. Burnat & al. (G-BU! [G00848006]); Crêtes du monte Nero sur le revers sud, env. de Zuccarello, 700–800 m, 27 Jun 1897, J. Briquet & F. Cavillier (G-BU! [G00848008]); Versant oriental du Mont Galero, extrem. or. des Alpes maritimes, aux env. de Garessio, 24 Jul 1880, J. J. Vetter & al. (G-BU! [G00848008; G00848009, four-sheet specimen]); Entre Albenga et Garlenda, Ligurie occid., 11 Jun 1879, É. Burnat (G-BU! [G00848010]); Mont Bignone près Albenga, 500 m, rocailles à l'ubac, silice, 5 Jun 1914, É. Burnat & al. (G-BU! [G00848011, twosheet specimen]); Mont Pisciavino près Albenga, 500 m, pentes herbeuses à l'ubac, grès, 5 Jun 1914, É. Burnat & al. (G-BU! [G00848012, three-sheet specimen]).

– “Leucanthemum vulgare var. eu-glaucophyllum” (Briquet & Cavillier in Burnat, Fl. Alpes Marit. 6: 104. 1916, nom inval., Turland & al. 2018: Art. 24.3).

Chromosome number — 2n = 90 (decaploid) (Favarger & Villard 1965, 1966).

Distribution — NW Italy (Liguria), where the species is endemic to the Ligurian Alps (Lo Presti & al. 2018).

New chromosome counts

3. Leucanthemum ×marchii Konowalik, Vogt & Oberpr., nothosp. nov. [= Leucanthemum glaucophyllum (Briq. & Cavill.) Jahand. x L. pallens (Perreym.) DC.].

Holotype: Italy, Liguria, Province Imperia, Alassio, summit of Monte Bignone above Vegliasco, 44°01.662′N, 08°09.766′E, 580 m, meadows and clearings in forest, 13 Jun 2011, R. Vogt 16942 & C. Oberprieler 10849, cult. Hort. Bot. Berlin, 8 Jul 2014 (B [B 10 0543018]).

Diagnosis — In terms of morphological characters with light brown bordered involucral bracts and ploidy levels of 7x / 8x (chromosome counts) and 9x (flow cytometry, C. Oberprieler and collaborators, submitted) intermediate between Leucanthemum glaucophyllum (Briq. & Cavill.) Jahand. (involucral bracts with dark brown margins; 10x) and L. pallens (Perreym.) DC. (involucral bracts pale; 6x).

Chromosome number — 2n = 63, 72 (heptaploid, octoploid) (Marchi & Illuminati 1974).

Distribution — NW Italy; hitherto observed only on the summit of Monte Bignone (Alassio).

Eponymy — This new nothospecies is named in honour of Dr. Palmer Marchi (Rome) in acknowledgement of his contributions to the knowledge of the genus Leucanthemum in Italy. He ascertained the chromosome number of this taxon for the first time and recognized its hybrid origin.

New chromosome counts

4. Leucanthemum subglaucum de Laramb. in Soc. Litt. Sci. Castres 4: 446. 1861 ≡ Leucanthemum maximum subsp. subglaucum (de Laramb.) Nyman, Consp. Fl. Eur. Suppl. 2: 169. 1889 ≡ Leucanthemum vulgare var. subglaucum (de Laramb.) Rony, Fl. France 8: 273. 1903 ≡ Leucanthemum vulgare subsp. subglaucum (de Laramb.) Bonnier, Fl. Ill. France 5: 95. 1922 ≡ Chrysanthemum subglaucum (de Laramb.) Braun-Blanq. in Commun. Stat. Int. Géobot. Médit. Montpellier 20: 312. 1933. – Ind. loc.: “Il habite les rochers les plus élevés au sommet de la montagne boisé, qui domine les ruines de l'ancien ermitage de Burlats, près Castres (Tarn), [...] Nous l'avons observé pour la première fois en compagnie de M. Contié, en juin 1859.“ – Lectotype (designated here): Burlas [Burlats] près Castres (Tarn), rochers granitiques, 14 Jun 1860, de Larambergue (P! [P00729951]).

– “Leucanthemum candolleanum” (Martrin-Donos, Pl. Crit. Tarn: 29. 1862, nom. inval., pro syn., Turland & al. 2018: Art. 36.1(b)).

– “Chrysanthemum leucanthemum subsp. subglaucum” (Guinochet & Vilmorin, Fl. France 4: 1451. 1982, nom. inval., Turland & al. 2018: Art. 41.5).

Chromosome number — 2n = 54 (hexaploid) (Favarger 1975).

Distribution — S France (Massif Central), where the species is endemic to the Cevennes and the Montague noire (Tison & de Foucault 2014).

Remarks — The sole available specimen collected prior to publication of the name Leucanthemum subglaucum is selected as as the lectotype.

New chromosome counts

5. Leucanthemum pallens (Perreym.) DC., Prodr. 6: 47. 1838 ≡ Chrysanthemum pallens Perreym. in Arch. Bot. (Paris) 2: 545. 1833; Pl. Phan. Fréjus: [91]. 1833 ≡ Chrysanthemum montanum var. pallens (Perreym.) Mutel, Fl. Franç. 2: 154. 1835 ≡ Tanacetum pallens (Perreym.) Sch. Bip., Tanaceteen: 35. 1844 ≡ Leucanthemum vulgare subsp. pallens (Perreym.) Bonnier & Layens, Tabl. Syn. Pl. Vasc. France: 166. 1894 ≡ Pontia pallens (Perreym.) Bubani, Fl. Pyren. 2: 223. 1900 ≡ Leucanthemum atratum subsp. pallens (Perreym.) Rouy, Fl. France 8: 269. 1903 ≡ Chrysanthemum leucanthemum var. [“δ”] pallens (Perreym.) Fiori in Fiori & Béguinot, Fl. Italia 3: 240. 1903 ≡ Leucanthemum vulgare “raç.” pallens (Perreym.) Samp., Lista Esp. Herb. Port.: 132. 1913 ≡ Chrysanthemum leucanthemum subsp. pallens (Perreym.) Braun-Blanq. in Bull. Acad. Int. Géogr. Bot. 28: 44. 1918. – Ind. loc.: “Esterel, le long de la route; juin”. – Holotype: Esterel, Perreymond misit Octobr. 1832, Herb. J. Gay (K! [ K000929449]).

Chromosome number — 2n = 54 (hexaploid) (Favarger & Villard 1965, 1966; Marchi 1972; Marchi & Illuminati 1974; Ritter 1974; Favarger 1975; Marchi & al. 1983; D'Ovidio 1986; Vogt 1991).

Distribution — NE Spain, S France, N Italy (Vogt 1991; Tison & de Foucault 2014; Lo Presti & al. 2018).

Remarks — This species displays a considerable resemblance to the tetraploid taxon Leucanthemum ircutianum subsp. leucolepis (Briq. & Cavill.) Vogt & Greuter, which is distributed in C and N Italy and in the Balkan Peninsula (Slovenia, Croatia, Bosnia and Herzegovina, Serbia). For a final decision on the delimitation of these two taxa, a more detailed study based on a denser sampling on the Apennine and Balkan Peninsulas is necessary.

The name and description of Chrysanthemum pallens Perreym. were provided (in litt.) by Jacques Étienne Gay, who examined herbarium specimens sent to him by Jean Honoré Perreymond. Gay's handwritten description is attached to the holotype specimen in his personal herbarium, which is kept in K ([ K000929449]).

New chromosome counts