We conducted field surveys in Sicily (Aeolian Islands, Nebrodi mountains, Peloritani mountains and Mt. Etna) from 2022 to 2024. Flowering and fruiting specimens of L. gredensis were collected in the south-eastern side of Etna volcano from five localities during spring 2024 (April to June). The collected specimens have been deposited in the CAT herbarium (the herbarium acronym follows Thiers 2024).

Additional information on the distribution of L. gredensis in Sicily were obtained from plant photographs published online by the members of the Facebook group “Flora spontanea Siciliana” (www.facebook.com/groups/floraspontaneasiciliana/) and from private photographic archives (R. Galesi and G. Siracusa pers. comm.).

Morphological observations were made on ten fresh individuals for each of the five populations of L. gredensis reported for Sicily. The specimina visa from these populations were compared with data from protologue and relevant literature (Merino 1895, Gandoger 1901, Castroviejo and Pascual 2000). In particular, the Sicilian specimens labeled as L. luteus, collected on Mt. Etna and stored in CAT and PAL herbaria, were examined to define their correct taxonomical attribution. Moreover, GBIF (Global Biodiversity Information Facility database, https://www.gbif.org/) records of L. gredensis from Portugal, Spain, Greece, and Turkey were examined. The comparison with the most similar species (L. luteus and L. hispanicus) was carried out using both fresh samples and scanned herbarium specimens preserved in ABH, CAT, GJO, PAL, PI, W, WAG. In particular, the three species have been differentiated on the basis of the following characters: stem indumentum, leaf upper surface, leaf stipules, corolla color, number of whorls in the inflorescences, and pod morphology (surface hairiness, position and beak).

Ten dry mature seeds of L. gredensis belonging to four different specimens from Mt. Etna, ten seeds of L. luteus belonging to five different specimens from Stromboli (Aeolian Islands) and two seeds obtained from the herbarium specimen CAT005493, were photographed using a scanning electron microscope (SEM) at an accelerating voltage of 10 kV. Specifically, Phenom XL G2 Desktop SEM was used. Seeds were directly mounted on to aluminium stubs with double adhesive tape and then sputter coated with gold. The images obtained where then analyzed using the software ImageJ, version 1.54 (Abramoff et al., 2004) to measure the perimeter and the area of 20 randomly selected palisade cells. The results were statistically compared with Student’s t-test, using software R, version 4.2.2 (R Core Team, 2022). No cells were measured from the two seeds sampled from the specimen CAT005493.

Vegetation relevés were sampled in the patches with high cover of L. gredensis, according to Braun-Blanquet’s methodology (Braun-Blanquet 1928). The phytosociological nomenclature mainly refers to Mucina et al. (2016) and the bioclimatological classification follows Bazan et al. (2015).

Lupinus gredensis, together with L. luteus and L. hispanicus, forms a well-supported taxonomic complex from a morphological and cytological point of view within the genus Lupinus L. (Castroviejo and Pascual 1998, 2000; Naganowska and Ladoň 2000). According to Euro+Med (2024), these three species are widespread in the Iberian Peninsula, while their presence in other Mediterranean territories may be considered as the result of an introduction although, according to numerous other sources (Pignatti 2017; POWO 2024), at least L. luteus can be considered native to the Italian Peninsula, Sardinia and Sicily.

The morphological study of the five populations found in Sicily has allowed a certain attribution of the material investigated to L. gredensis (Fig. 1). This taxon is easily distinguishable from all the other species known for Italy by the color of the corolla. The only native species that shows some affinity with it is L. luteus L. that, however, always has flowers with an intense yellow corolla and densely hairy leaves on both blades. Lupinus gredensis clearly differs from L. luteus for other morphological characters, such as: leaves glabrous on the upper blade or with hairs only on the margin; inflorescence generally with less than 11 whorls; flower peduncles longer than 2 mm; ripe pod yellowish-brown (vs dark brown), almost erect before maturation, with 5–7 (vs 4–5) seeds, often adorned with a colored arch towards the hilum. Finally, the leaf stipules, in L. luteus, are dimorphic: linear in the basal leaves and foliaceous in the upper ones. The flowers of L. hispanicus, are lilac to violet throughout flowering; it has appressed-hairy stem, shorter inflorescence with 3–7 whorls and tuberculated seeds (Boissier and Reuter 1842; Castroviejo and Pascual 1998, 2000). The main diacritical characters of these three species are listed in Table 1 and illustrated in Fig. 2.

Figure 1. 

Lupinus gredensis in Sicily A habitat in wood clearings B detail of inflorescence C habitus D leaf blade E L. gredensis in the undergrowth of vegetation with Pteridium aquilinum F immature pods. In F the whitish colour of the leaves is due to a fungal infection.

Figure 2. 

Illustration of Lupinus gredensis and of the related species L. luteus and L. hispanicus. L. gredensis (A), L. luteus (B) and L. hispanicus (C). 1. Inflorescence. 2. Leaves. 3. Pod. 4. Seed. Drawings by Rosaria Di Cicca.

Here we give provide a description of the Sicilian plants, which agrees with Castroviejo and Pascual (2000):

Annual herb 15–80 cm tall, from villous-hairy to hairy. Stem generally branched from the base, with prostrate-ascending stems. Leaves with petiole 9.7–12.1 cm long, divided into 5–9 leaflets of 20–72.2 × 6.9–18.3 mm, mucronulate in the lower leaves, oblanceolate in the upper ones, glabrous or slightly hairy at the margin in the upper blade, appressed hairy in the lower one; stipules linear, 9.5–15.7 mm long with membranous margin. Inflorescence 7.5–26.1 cm long, constituted by 5–10 whorls of 5 flowers each; pedicels 1.8–2.7 mm long; bracts ovate-oblong, sharp, deciduous; bracteoles linear. Calyx bilabiate, with appressed to sub-patent sericeous hairs; upper lip fissured almost to the base, 5.9–7.3 mm long; lower lip tridentate, 7.3–9.3 mm long. Corolla pale yellow in the upper 3–4 whorls, pink or lilac in the central and lower whorls. Standard 14.2–18.4 × 8–11.1 mm; wings 15.5–17 × 7.3–9 mm; keel 12.6–14.7 × 3.8–4.8 mm. Ferruginous-brown, patent-hairy legume, up to 65 mm long and up to 11 mm wide, almost erect before maturation, ending with a sharp, erect-patent beak of 8–10 mm, with 5–7 seeds. Seeds 4.6–6.2 mm in diameter, lenticular to globose-lenticular, generally white with a colored arch near the hilum and a smooth head.

According to various authors (Heyn and Herrnstadt 1977; Aȉnouche and Bayer 2000; Aȉnouche et al. 2004; Marzouk 2006), the microstructure of the seed coat and the unicellular pattern of microsculptures represent significant taxonomical characters in the genus Lupinus, which allow distinguishing the different taxa. The micromorphological investigation of seed coat (Fig. 3) of L. gredensis revealed a smooth surface with very cohesive and prominent isodiametric palisade cells (macrosclereids). The outer periclinal wall of these cells is characterized by irregular microsculptures with curved tips, while the anticlinal walls look from slightly curved to straight. As concerns L. luteus, previously examined by Mahé (2011), the cells are significantly (p < 0.005) greater (area = 143.13 µm² ± 6.29 SE; perimeter = 47.43 µm ± 1.06 SE) and with a surface more prominently sculptured if compared to L. gredensis (area = 32.00 µm² ± 1.72 SE; perimeter = 22.13 µm ± 0.69 SE). Besides, L. luteus shows a different micromorphological pattern, as well as less marked and quite obscure anticlinal walls. Although it was not possible to take precise measurements on the seeds sampled from the herbarium specimen CAT005493, the microstructure patterns of the periclinal walls and the cell size are more similar to those of L. gredensis rather than L. luteus. However, both L. luteus and L. gredensis fully belong to the group of smooth seeded lupins for the cohesive and isodiametric external palisade cells.

Figure 3. 

SEM micrographs of seed. Lupinus gredensis: A whole seed view (× 37) B seed coat view (× 2900) C detail of seed coat (× 14000). Lupinus luteus: D whole seed view (× 37) E seed coat view (× 2900) F detail of seed coat (× 14000).

An analytical key for recognizing the various taxa belonging to the Lupinus genus in Italy is shown below.

Field investigations allowed to ascertain the occurrence of at least five populations, all located on the south-eastern side of Mt. Etna and precisely in the territories of Trecastagni, Nicolosi, Pedara, and Zafferana Etnea. However, based on the analysis of photographic material published online (www.facebook.com/groups/floraspontaneasiciliana/) or stored in private photographic archives (R. Galesi and G. Siracusa pers. comm.) and kindly made available, it can be assumed that this species is also present in other areas, often in localities adjacent to those known to us (Fig. 4). Further data on the distribution of this species were provided by the review of herbarium specimens labeled as L. luteus which, as far as the Mt. Etna area is concerned, are often referable to L. gredensis. The locations reported in the oldest specimens, although often not very precise, are largely comparable with those detected by field investigations. The only locality quite distant from the other populations is located in the surroundings of Randazzo (northern side of Etna), as recorded by a specimen collected by S. Tricomi in 1913 (CAT005495) and another in 1989 (CAT112411).

Figure 4. 

Distribution of Lupinus gredensis on Mt. Etna (Sicily). Data obtained from field investigations (circles); herbarium specimens (triangles); photographic documentations (stars).

In Sicily, L. gredensis grows only on volcanic sands at altitudes between 700 and 1,100 m a.s.l., colonizing clearings of deciduous or holm oak forests, roadsides and uncultivated lands. As highlighted by Milla et al. (2011), L. gredensis shows lower fitness and a competitive disadvantage compared to L. angustifolius, widespread in the same environments, being much less abundant than the latter. Lupinus gredensis is able to form denser populations only in the presence of substrates characterized by highly incoherent and poorly developed soils with a very fine texture, where competition with L. angustifolius and other ruderal species is less marked. Overall, the observed ecological preferences coincide with those reported by Castroviejo and Pascual (2000) and by Costa et al. (2012) in the Iberian Peninsula. In fact, according to these authors, L. gredensis colonizes abandoned crops, grasslands and degraded scrubs in siliceous or decarbonated soils up to 1,500 m a.s.l. As regards the Bulgarian populations, they occur mainly on ruderal habitats on siliceous substrates up to 700 m, along roadsides and uncultivated lands (Stoyanov and Apostolova-Stoyonova 2022).

According to field and herbarium investigations, the occurrence of L. luteus in Sicily is confirmed in numerous other areas of the island, such as on the Peloritani and Nebrodi mountains, western Sicily (Ficuzza and Alcamo), the Aeolian islands, and Pantelleria (Giardina et al. 2007). On Mt. Etna, its occurrence can be confirmed only in the basal thermo-Mediterranean belt of the eastern side between 100 and 350 m, as resulting from our observations and from the literature (Musmeci 2024). From the ecological point of view, this species is linked to dry meadows on siliceous soils (mainly quartzarenites, metamorphites and vulcanites) from sea level to 600 m a.s.l.

This species has been found in various plant communities, although it is mainly linked to aspects of ruderal vegetation attributable to the class Chenopodietea Br.-Bl. in Br.-Bl. et al. 1952. In particular, L. gredensis sometimes colonizes the clearings and edges of mesophilous woods belonging to the class Quercetea ilicis Br.-Bl. ex Molinier 1934 or is represented in sub-nitrophilous communities characterized by Pteridium aquilinum (L.) Kuhn, linked to stations with deep and fertile soils (Brullo and Marcenò 1985). However, the most characteristic populations of L. gredensis can be referred to a ruderal community linked to siliceous sandy soils (Table 2), belonging to the order Brometalia rubenti-tectorum (Rivas Goday & Rivas-Mart., 1973) Rivas-Mart. & Izco, 1977. Due to its ecological and floristic peculiarities, we consider appropriate to describe a new association, namely Linario aetnensis-Lupinetum gredensis Cristaudo & Cambria, ass. nov. (holotypus: Table 2, rel. 2, hoc loco). This association, fairly poor from a floristic point of view, is clearly dominated by L. gredensis accompanied by few other species with low coverage, such as Linaria multicaulis (L.) Mill. subsp. aetnensis Giardina & Zizza, Lupinus angustifolius, Anisantha tectorum (L.) Nevski, Isatis tinctoria L. subsp. canescens (DC.) Arcang. Overall, this community shows a pioneer character in the colonization of coarse sandy soils and is found mainly in uncultivated and large woodland clearings. From a bioclimatic point of view, this vegetation belongs to the meso-Mediterranean belt with a humid ombrotype.