Introduction

The genus Senecio L. (Asteraceae, Senecioneae) is one of the largest genera of flowering plants and comprises c. 1250 species (Bremer 1994; Pelser 2007; Nordenstam 2007; Calvo & al. 2015). The origin of Senecio is hypothesized to be the SW parts of Africa around the Miocene from where its Palaearctic colonization began with different lineages (Kandziora & al. 2016). Today, it is almost cosmopolitan, although remarkable diversification occurs mainly in the Mediterranean climate zones, i.e. South Africa, Chile, and the Mediterranean Basin (Nordenstam & al. 2009; Calvo & al. 2015).

Senecio apenninus Tausch was first described generically from the Apennines (Tausch 1828). This taxon was treated at varietal rank by Fiori (1927) and Zangheri (1976) as S. doronicum var. apenninus (Tausch) Fiori distributed from Piceno Apennine to Cervialto. It was not recognized in Flora europaea (Chater & Walters 1976) and in Flora d'Italia as well (Pignatti 1982). Senecio apenninus gained again species validity in An annotated checklist of the Italian vascular flora (Conti & al. 2005), quoted in Marche, Umbria, Lazio, Abruzzo, and Molise. Greuter (in Greuter & Raab-Straube 2008) regarded S. apenninus as synonym of S. provincialis (L.) Druce. Recently, Pignatti (2018) listed it in note to S. provincialis, and in the updated checklist of the vascular flora native to Italy (Bartolucci & al. 2018), it was regarded as a synonym of S. doronicum subsp. orientalis J. Calvo.

According to the recent systematic revision of Senecio sect. Crociseris (Rchb.) Boiss. (Calvo & al. 2015), S. doronicum (L.) L. occurs in SE Europe, from the Cantabrian Mountains to the N Dinaric Alps and it is characterized by 1–4(–9) capitula, which are relatively large, usually showing supplementary bracts as long as the involucral ones, and basal leaves lanceolate to oblanceolate, attenuate, ± concolorous. Within S. doronicum three subspecies are currently recognized: subsp. doronicum, subsp. orientalis and subsp. longifolius (Willk.) J. Calvo. Senecio doronicum subsp. doronicum is distributed in Austria, France, Germany, Switzerland and N Italy; S. doronicum subsp. orientalis, recently described based on a specimen collected in the C Apennines (Calvo & al. 2015), is an amphi-Adriatic taxon occurring also in the E Alps, and in some localities overlaps with S. doronicum subsp. doronicum (i.e. M. Baldo, Veneto and Trentino-Alto Adige, Italy); S. doronicum subsp. longifolius is distributed from Cantabrian Mountains and Pyrenees to SE France. Senecio provincialis is regarded by Calvo & al. (2015) as a good species distributed in France and Spain, differing from S. doronicum in supplementary bracts widened at the base, ± imbricate, usually a quarter to three quarters as long as involucral bracts, and basal leaves ovate to lanceolate, rounded to cuneate (rarely attenuate), ± discolorous. Senecio provincialis was also recently recorded from the W Alps in Italy (Bartolucci & al. 2018).

Senecio apenninus is considered by Calvo & al. (2015) as likely similar to S. doronicum subsp. orientalis, but with remarkable morphological characters such as long peduncles, small capitula, and short supplementary bracts, a quarter to a half as long as the involucral ones. Even so, due to the few samples studied, Calvo & al. (2015) placed it under “Doubtful or excluded names”.

Fig. 1.

Distribution map of Senecio apenninus (blue dots) and S. doronicum subsp. orientalis (red dots) according to herbarium specimens used for morphometric analysis.

According to our preliminary study on herbarium material (see  Appendix 1, supplemental content online (wi.49.49304_supplement.pdf)) matching Tausch's protologue and identifiable as Senecio apenninus from C Italy, it is evident that the latter species is morphologically homogeneous and clearly different from S. doronicum mainly for small capitula, 4–15 up to 50 capitula (vs 1–4(–9)), very short supplementary bracts, ± half as long as the involucral ones (vs two thirds to one and a half as long as the involucral ones) and from S. provincialis mainly for leaves lanceolate to oblanceolate, obtuse to acute, attenuate to cuneate, concolorous (vs ovate to lanceolate, rounded to cuneate, rarely attenuate, ± discolorous), involucral bracts lanceolate to ensiform (vs lanceolate to oblong), supplementary bracts subulate, without scarious margin, not imbricate (vs broadly lanceolate to triangular sometimes with scarious margin, ± imbricate), and 4–15 up to 50 capitula (vs 1(–4)).

Table 1.

Morphological characters employed in the morphometric analyses.

In order to correctly classify Senecio apenninus, we carried out a morphometric analysis, that aims to clarify its taxonomic value and to examine its morphological variability. Considering the morphological traits discussed above and the distribution of the taxa cited, we compared S. apenninus with the related S. doronicum subsp. orientalis, the only taxon occurring in the same area (C Apennines, Italy).

Material and methods

This study is based on an extensive analysis of relevant literature, field surveys and detailed examination of herbarium specimens kept in APP, COI, FI, K, MPU, NAP, NY, P, PESA, PI and US (see  Appendix 1,, supplemental content online (wi.49.49304_supplement.pdf)). The original material for the name Senecio apenninus was searched in BUC, CGE, LE, PH, PR, PRC, REG, W and WU (herbarium codes follow Thiers 2019+). The morphometric analyses, based on measurements of both qualitative and quantitative characters, were carried out on 85 selected specimens (Fig. 1) including S. apenninus (42 specimens) and S. doronicum subsp. orientalis (43 specimens). The analyses were performed on 38 variables (Table 1), selected according to their common use for taxonomic identification of Senecio (Calvo & al. 2015).

Micromorphological analysis was carried out by stereo-microscope on stem, leaves, floral elements (petals, androecium and gynaecium) and fruits. For each specimen, ligulate florets, tubular florets, filaments, anthers, supplementary bracts and involucral bracts were soaked in water for a few seconds before measurements were taken. Parameters were measured, after scanning, using ImageJ software (Rasband 1997–2016) or simply with a ruler. Measurements refer to dried specimens.

For each quantitative character, Shapiro-Wilks normality test was first used to determine their distribution and then independent sample t-tests were used to analyse their differences and thereafter box plots were made in R studio version 1.1.463 (R Core Team 2019). To include the qualitative characters in the multivariate analysis, a matrix was developed based on individual character distribution (see Table 1). Several multivariate approaches were used to compare all the evaluated characters in both taxa including principal component analysis (PCA), Bray Curtis-based non-metric dimensional scaling (NMDS), unweighted pair group method with arithmetic mean (UPGMA) cluster analysis, and Pearson (linear) correlation in PAST [PAlaeontological STatistic] package version 3.24 (Hammer & al. 2019). Prior to the analysis, all the characters were normalized using the software's correlation matrix as previously adopted and described by Wahlsteen & Tyler (2019). Pearson's correlation was used to show the relationship between the traits studied. The PCA was used to analyse matrices of several characters and species to get a general overview of the variation in the two groups. NMDS is a numerical technique with the capability to produce a dissimilarity-based index data matrix that places data points in a dimensional coordinate system so that relative distances between points reflect the relative dissimilarity between samples (Laflamme & al. 2011; Hammer & al. 2019). This technique can highlight the taxonomic significance of characters included in a study (Liu & al. 2013). UPGMA-based cluster analysis was performed with arithmetic mean, Michener & Sokal 1957) and Gower similarity index (Gower 1971).

Table 2.

Comparisons of morphological characters between Senecio apenninus and S. doronicum subsp. orientalis. Quantitative continuous characters are expressed in mm and are reported as mean ± standard deviation and 10–90 percentiles (extreme values in brackets). For quantitative discrete characters, 10–90 percentiles are given (extreme values in brackets).

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Table 3.

T score and P value of quantitative characters evaluated (significant P values at P < 0.05 in boldface).

Furthermore, the variability of the analysed morphological characters was described by standard statistical parameters (mean, standard deviation, minimum, maximum, 10th and 90th percentiles) (Table 2).

Results

Analysis of vegetative and reproductive morphological features (Table 2) of Senecio apenninus and S. doronicum subsp. orientalis allows the recognition of two clearly distinct and separate taxa. The most diagnostic features are the length of supplementary bracts and in particular the ratio of length between involucral bracts and supplementary bracts, the diameter of capitula and the number of capitula.

Fig. 2.

Boxplots expressing morphological variation between Senecio apenninus and S. doronicum subsp. orientalis: plant height, number of capitula, diameter of capitula, length of involucral bracts, length of supplementary bracts, ratio length involucral bracts / supplementary bracts, length of pappus, length of anthers. Outlined central box depicts middle 50% of data, extending from 25th and 75th percentiles, and horizontal bar is the median. Ends of vertical lines (or “whiskers”) indicate minimum and maximum data values, unless outliers are present, in which case whiskers extend to a maximum of 1.5 times inter-quartile range. Circles indicate outliers, unless extreme outliers are present, in which case circles extend to a maximum of three times inter-quartile range and extreme outliers are indicated as asterisks.

Fig. 3.

PCA scatter plot revealing distinction between Senecio apenninus (blue dots) and S. doronicum subsp. orientalis (red dots).

Most of the quantitative morphometric characters evaluated showed significant differences between the two Senecio taxa with the exception of LPBL, WIB and WLF (Table 3).

The means of each quantitative character were compared between the two taxa including PLH, NoC, DoC, LIB, LSB, RoIB/SB, LoP and LoAT (Fig. 2).

Overall, Pearson correlation coefficient reveals significant correlations between several characters. However, no character was excluded based on their correlation. The PCA produced eight components with eigenvalues greater than one (see  Appendix 2, supplemental content online (wi.49.49304_supplement.pdf)). The first and second component explained 47.61% and 20.11% of the variance, respectively. A scatterplot of the first two components (Fig. 3) shows a distinction between the two Senecio taxa. Character loadings of the eight components with eigenvalue greater than one reveal that DoC, NoC, NSB, NIB, LSB, LIB and LLF were the most influential characters in this analysis (see  Appendix 3, supplemental content online (wi.49.49304_supplement.pdf)).

The UPGMA dendrogram based on Gower similarity clearly separated Senecio apenninus (blue) and S. doronicum subsp. orientalis (red), suggesting more differences between the taxa and less within (Fig. 4). The two well-delimited clusters suggest they may be considered as independent taxa. This was further supported by the NMDS plot (Fig. 5), which grouped the individuals from the two taxa separately. The two clusters in the NMDS plot were exclusive for each group suggesting the possible separation of individuals from the two taxa.

Taxonomic treatment

Senecio apenninus Tausch in Syll. Pl. Nov. 2: 252. 1828. – Neotype (designated here): Italy, Lazio, M. S. Venanzio in loc. Selva Rotonda, Cittareale (Rieti), WGS84 33T: 345763 E, 4719023 N, pascoli secondari al margine della faggeta, 1616 m, 17 Jun 2016, F. Conti, F. Bartolucci & R. Pennesi (APP No. 57529; isoneotypes: APP Nos. 57499, 57528, 57530, 57531, 57532, 57533, 57534, 57535, 57536, 57537, 57538, 57539, 57540, 57541). – Fig. 6.

Description—Perennialherb.Stem(42–)45–78(–93)cm tall, erect, leafy, corrugated, solid, not branched, glabrescent to arachnoid, base usually without remnants of old leaves or tufts of hairs. Largest basal leaves (6–)7–14.8(–15.5) × (1.5–)2.2–5.3(–7.5) cm, persistent, occasionally withering early, lanceolate to oblanceolate, obtuse to acute, attenuate to cuneate, with a petiole (2–)3–11(–20) cm, dentate to slightly dentate, sometimes subentire, glabrescent to covered with scattered arachnoid trichomes above, arachnoid beneath, concolorous. Cauline leaves 3–7; largest cauline leaves (4.3–)9–19.5(–27) × (0.5–)1.4–4.3(–8) cm, alternate, lanceolate to oblanceolate, acute, rarely obtuse, sessile to semi-amplexicaul auriculate, rarely attenuated into a petiole, dentate to slightly dentate, rarely subentire, glabrescent above, arachnoid beneath, tertiary venation inconspicuous. Synflorescence corymbose, with linear bracts. Capitula (3 or)4–15(–50), (25–)28–38(–42) mm in diam., on long peduncles (to 23 cm); involucre cupuliform; involucral bracts (18–)20–24(–28), (6.6–)6.9–8.9(–9.5) × (0.9–)1–1.6(–1.9) mm, with scarious margin 0.05–0.35 mm wide, lanceolate to ensiform, acute, 0–2-keeled, apex usually with a blackish spot, glabrescent to weakly arachnoid; supplementary bracts (7 or)8–16(–18), (3.2–)3.3–5.3(–7) × (0.4–)0.5–0.9(–1) mm subulate, without scarious margin, apex usually with a blackish spot, [ratio length involucral bracts / supplementary bracts = (1.3–)1.5–2.2(–2.5)], arachnoid, not imbricate. Ligulate florets yellow, (11.5–)13.2–20.1(–20.7) × (2.8–)3.1–4.6(–5.1) mm, with tube (2.8–)3–4.7(–5.4 mm; t (2.1–)3–5.1(–5.5) mm. Achenes 4.7–5.2 × 1–1.4 mm subcylindric, shorter than pappus, with 9–11 ribs, glabrous, with scattered scales near base c. 0.06 mm; pappus (3.7–)4–5.8(–6.1) mm, whitish.

Fig. 4.

Hierarchical clustering of 85 specimens of Senecio apenninus (blue) and S. doronicum subsp. orientalis (red) based on all evaluated characters using a paired group algorithm (UPGMA) and Gower similarity index.

Fig. 5.

Bray Curtis-based non-metric multidimensional scaling (NMDS) plot of 85 specimens of Senecio apenninus (blue dots) and S. doronicum subsp. orientalis (red dots) based on 27 morphometric characters.

Phenology — Flowering in June–July, fruiting in July–August.

Distribution — Senecio apenninus is endemic to the C Apennines, widespread in Umbria, Marche, Lazio and Abruzzo. The occurrence in Molise recorded by Lucchese (1995) without locality needs confirmation. We were not able to trace any herbarium specimens from Molise region.

Ecology — Meadows, edges and clearings of forests of Fagus sylvatica L.

Conservation status — According to IUCN criteria (IUCN Standards and Petitions Subcommittee 2017), we propose to include Senecio apenninus in the following category: Least Concern (LC).

Remarks — Tausch (1828: 252) described Senecio apenninus from the Apennines without any specific collection locality with a short description: “corymbo paucifloro inaequali, involucris anthodio duplo brevioribus; foliis denticulatis glabris, inferioribus ovatis obtusis petiolatis, superioribus lanceolatis acutis subamplexicaulibus”. The author added also some differences between S. doronicum and S. apenninus: “Proximus S. doronico L. sed differt corymbo sub 4-floro prolifero, pedunculis nempe inferioribus longioribus, nec furcatis; floribus duplo minoribus pallidis; involucro anthodium non adaequante”. According to Stafleu & Cowan (1986), Tausch's herbarium is housed in PRC (duplicates in PR, Mráz P., in litt.). Others duplicates are kept in BUC, CGE, LE, PH, REG, W, WU. We were not able to trace any original material in the above-mentioned herbaria. Even Calvo & al. (2015) were not able to find it. In PRC the Asteraceae (former German University herbarium) collection has not been yet merged with the Czech herbarium and then accessible for research purposes (Mráz P., in litt.). Thus, we select a specimen collected in the C Apennines during the annual field trip of the working group for Floristics, Systematics and Evolution of the Italian Botanical Society held in 2016 (Bartolucci & al. 2019), which matches Tausch's protologue (long peduncles, small capitula, and short supplementary bracts), as neotype (see Art. 9.13 of the International Code of Nomenclature for algae, fungi, and plants; Turland & al. 2018).

Fig. 6.

Senecio apenninus – A: lower part of plant showing basal and lower cauline leaves; B: upper part of plant showing upper cauline leaves and synflorescence; C: involucre with distal portion of peduncle; D: achene with pappus; E: tubular floret. – Source: Italy, Marche, Gruppo del Montigno, Valle del Forno, tra Casa di Corradino e la Fonte del Forno, 6 Jul 1979, A. Brilli-Cattarini & L. Gubellini (PESA). – Drawn by L. Gubellini.

Discussion

The present work revaluates Senecio apenninus, an endemic species of the C Apennines, widespread in Marche, Umbria, Lazio, Abruzzo and doubtfully occurring in Molise. Senecio apenninus is easily recognizable by the length of supplementary bracts and in particular by the ratio of length between the involucral bracts and supplementary bracts, capitula size, and number of capitula. Our results support the recognition of S. apenninus at specific rank as it shows peculiar characters, taxonomically more relevant, than those used by Calvo & al. (2015) for the description of the intraspecific variability of S. doronicum and also because it is sympatric with S. doronicum subsp. orientalis.

Contrary to what was observed by Calvo & al. (2015) Senecio doronicum subsp. orientalis has frequently and not rarely a single capitulum. Also, in Calvo & al. (2014) the number of capitula, the length of supplementary bracts and leaves with glabrescent to arachnoid indumentum are key characters of S. doronicum subsp. orientalis, which are supported by the results from the present study as they discriminated between the two evaluated taxa. According to our study S. doronicum subsp. orientalis and S. apenninus can occur in the same localities and they are sympatric in some places.

Senecio apenninus adds to the large contingent of endemic taxa occurring in the Apennines, some of which were recently described (i.e. Peruzzi & al. 2007; Conti & Bartolucci 2017; Conti & al. 2018, 2019; Rosati & al. 2018). Many of these taxa are endemic of C Italy, such as Adonis distorta Ten., Cardamine apennina Lihová & Marhold, Corydalis densiflora subsp. apennina F. Conti & al., Erodium alpinum (Burm. f.) L'Hér., Gagea tisoniana Peruzzi & al., Iris marsica I. Ricci & Colas., Lathyrus apenninus F. Conti, Noccaea stylosa (Ten.) Rchb., Oxytropis ocrensis F. Conti & Bartolucci, Paeonia offici-nalis subsp. italica N. G. Passal. & Bernardo, Ranunculus giordanoi F. Conti & Bartolucci, Saxifraga exarata subsp. ampullacea (Ten.) D. A. Webb, Silene notarisii Ces., etc. According to Bartolucci & al. (2018), 1707 taxa are endemic to Italy, Italy and Corsica (France), or Italy and Malta and among these, 1340 are narrow endemics to Italy (subspecies of Hieracium L. and Pilosella Hill excluded, see also Peruzzi & al. 2014, 2015, continuously updated online). Italy appears to be one of the Mediterranean countries with the highest number of endemic taxa (Peruzzi & al. 2014). The endemic taxa are key elements for setting national, regional or local conservation priorities and for driving conservation strategies (Orsenigo & al. 2018).