Solenopsis laurentia ( Linnaeus 1753: 931 ) C. Presl (1836: 32)

Brullo, Salvatore, Brullo, Cristian, Cambria, Salvatore, Minissale, Pietro, Sciandrello, Saverio, Tavilla, Giuseppe Siracusa Gianmarco, Tomaselli, Valeria & Galdo, Gianpietro Giusso Del, 2023, Taxonomical remarks on Solenopsis laurentia (Campanulaceae) in Italy, Phytotaxa 584 (2), pp. 59-88 : 63-71

Solenopsis laurentia ( Linnaeus 1753: 931) C. Presl (1836: 32)

Lobelia laurentia Linnaeus (1753: 1931) ; Type:—Icon. Tab. 14, Micheli (1729) as “ Laurentia annua, minima, flore caeruleo ” pg.18, (lectotype designated by Crespo et al., 1996) ( Fig. 1 ).

Epitype:— ITALY. Tuscany: Insula Elba (olim Ilva vel Aetalia), fra il golfo Stella e il golfo dell’Acoreo (andando dal Margidore alla spiaggia grande) pareti delle fosse, ivi abbondante, 28 June 1900, S .

Sommier s.n. (FI! Specimen bottom right, sub Laurentia michelii , here designated).

Lobelia gracilis Salisbury (1796: 129) , nom. Illeg.

Laurentia michelii A. Candolle de (1839: 409).

Lobelia michelii (A. Candolle de) Colmeiro (1887: 493), nom illeg.

Laurentia commutata Todaro (1873: 160) , nom illeg.

Description: —Annual herb, 8–13 cm tall, scapose, elongate, glabrous, green. Stems solitary, erect, laxly leafy and unbranched below, more densely leafy and branched at the top. Leaves usually cauline, 10–20 × 3–6 mm, oblanceolate to spathulate, entire to weakly crenate, petiolate, penninerved. Petiole 3–5 mm long. Flowers solitary on axillary pedicel, 2–6 cm long, with 1–2 bracteole 2.5–3.5 × 0.4–0.9 mm, with 1–3 small teeth per side ending with a gland and apex without gland. Calyx 3–4 mm long, with lobes linear-lanceolate, acute, 1.5–2.2 mm long, uninerved, smoot at margin. Corolla tubular, 5–6 mm long, bilabiate, with lobes slightly divaricate, oblong, acute to sub-obtuse, upper lip with 2 lobes 2.5–2.7 × 1.1–1.3 mm, bluish-lilac and whitish in the lower part of the tube, lower lip with 3 lobes 1–1.2 × 0.7–0.8 mm, bluish-lilac, whitish in the tube and slightly tinged with green in the central part of the nervation. The lower lobes inside are provided with papillae clavate, 0.12–0.3 mm long, 25–50 per each lobe. Staminal filament whitish, 2.5–3.1 mm long, below fused with the corolla. Anthers violet, upper bearded, connate into a tube 0.7–0.8 mm long, wholly encapsulating the stigma; the two lower anthers are smaller, each at the top with a tuft of hairs closing a narrow fissure; the three upper anthers in the young flower are curved and at the end erect, with hairs near the top of the back. Ovary below fused with the calyx tube; style whitish, slightly curved upward 3 mm long; stigma white, papillate, with a ring of hairs just under the base. Capsule 3 mm long. Seeds flat, ellipsoid, brownish-yellow, shining, 0.4 × 0.2 mm.

Seed micromorphology: —According to literature ( Murata 1992, 1995, Haridasan & Mukherejee 1993, Serra & Crespo 1997, Crespo et al. 1998), the ornamentations of the seed coat surface in the Lobelioideae subfamily of Campanulaceae have a remarkable diagnostic value and also a phylogenetic significance. In fact, the testa structure of mature seeds is well defined and constant for a given species or group of allied species. As concerns Solenopsis , it was investigated by Serra & Crespo (1997), Crespo et al. (1998) and Brullo et al. (2013), who emphasized that the seed coat sculptures are quite similar in the species of this genus. In particular, the seed testa is longitudinally furrowed by long and narrow cells, which are incised on the back by a superficial groove. The SEM observation carried out on the subspecies of Solenopsis laurentia emphasized that although there are significant similarities in the features of their seed testa, some morphological differences can be detected, which represent an additional support to their taxonomic identification. In particular, the cells covering the seed testa show more differentiation in the subsp. caespitosa ( Fig. 2C ), since the periclinal walls are those to have a greater width (5–5.8 μm), while in the subsp. gasparrinii ( Fig. 2B ) they are those to have a smaller width (2.5–3 μm). Conversely, the other subspecies have periclinal walls of intermediate size between the previous two (4–5 μm). In addition, in the subsp. caespitosa ( Fig. 2C ) and subsp. hyblaea ( Fig. 2D ) the periclinal walls are flatter with shallow anticline walls. Otherwise, the other three subspecies have markedly convex periclinal walls and more furrowed anticlinal walls ( Fig. 2 ). Finally, the subsp. laurentia ( Fig. 2A ) and subsp. parvula ( Fig. 2E ) are characterized by cells with periclinal and anticlinal walls very similar, but they differ markedly in the size of the seeds, since the first one has longer seed (0.40 mm), while the second one has smaller seed (0.35 mm).

Pollen grains micromorphology: —SEM investigations carried out on dried pollen grains of Solenopsis laurentia subspecies revealed that all populations studied are 3-colporate with a perplorate shape. Their dimensions range from 26–46 μm in length and 13–16 μm in width, with sexine reticulate-striate characterized by branched lirae delimiting small lumina ( Figs. 3–4 ). Previously, observations on pollen of this species s.l. were recorded by Dunbar (1975), who examined at light microscope an Iberian population without providing any photos of this material. As concerns the subspecies here examined, they show some morphological differences in the size and sexine ornamentations. In particular, the subsp. laurentia ( Figs. 3A , 4A ) is characterized by larger pollen grains (46 × 14 μm) with very prominent reticulum and lirae markedly anastomosed of variable thickness, with many lumina of different shape; the subsp. gasparrinii ( Figs. 3B , 4B ) has pollen grains slightly smaller than the previous one (40×16 μm) with more dense reticulum and lirae poorly anastomosed, with a few number of lumina smaller in size; the subsp. caespitosa ( Figs. 3C , 4C ) has even smaller pollen grains than the previous one (30 × 14 μm) with reticulum and lirae quite similar to subsp. laurentia ; the subsp. parvula ( Figs. 3D , 4D ) has pollen grains smaller than the previous ones (26×15 μm) with flatter reticulum and lirae less prominent, the lumina numerous and quite large; the subsp. hyblaea ( Figs. 3E , 4E ) has pollen grains with similar size to previous ones (26 ×13 μm) with more compact reticulum and thick lirae, the number of lumina is less and usually smaller in size.

Nomenclatural notes:—This species was described by Linnaeus (1753) as Lobelia laurentia , mentioning three synonyms: “ Laurentia annua minima , flore caeruleo ” Micheli (1729: 18, t.14); “ Rapunculus aquaticus repens , flore caeruleo inaperto ” Ray (1704, 383); ibid. Boccone (1697, 335, t.27). Among these syntypes, Crespo et al. (1996) designated the iconography illustrated by Micheli as lectotype. Since, it is a poorly detailed illustration that does not allow a precise application of the name to the taxon (art. 9.9., ICN, Turland et al. 2018), one herbarium specimen (FI) coming from Elba Island, which is its locus classicus (see Micheli 1729), is here designated as epitype. Besides, the name Lobelia gracilis Salisbury (1796: 129) is illegitimate, since it is a superfluous name for Lobelia laurentia , which Salisbury cited explicitly as synonym (art. 52.2, ICN). Later, Candolle de (1839: 409) transferred Lobelia laurentia to the genus Laurentia , proposing for it the new name Laurentia michelii , which represents a legitimate name (art. 23.4). Later, Todaro (1873: 160) also proposed Laurentia commutata as replacement name for Lobelia laurentia Linnaeus , but it represents an illegitimate name for Laurentia michelii DC.

According to art. 10.2 (ICN), Lobelia laurentia was designated by Crespo et al. (1998: 216) as type of genus Solenopsis , described by Presl (1836), within which he included five species. This genus was treated as a section of the genus Laurentia by Endlicher (1838: 512), while Petermann (1845: 444) thought it better to consider it a subgenus of the latter (see Crespo et al. 1998).

Etymology:—As epithet Linnaeus (1753) used the same name proposed by Micheli (1729) to commemorate M. A. Laurenti (1678–1772), famous medic of Bologna ( Italy).

Distribution and ecology: — Solenopsis laurentia is an annual hygrophilous plant growing usually with several other microphytes in the wetlands, represented mainly by temporary ponds, localizing often in very small surfaces. It likes stands with sandy-silty soils, drying up since the early spring, from coasts to sub-mountain belt throughout the Mediterranean area, Canary Islands included. According to literature data ( Damboldt 1978, Mouterde 1978, Crespo et al. 1998, Sales & Hedge 2001, Le Floc’H et al. 2010, Dimopoulos et al. 2013, Fennane & Mathez 2014, Tison & de Foucault 2014, Brullo & Guarino 2018), this species is distributed in Portugal, Spain, Balearic Islands, France, Corse, Italy, Sardinia, Sicily, Greece, Crete, Turkey, Lebanon, Tunisia, Algeria, Morocco and Canary Islands. Based on our morphological investigations carried out on the living populations, Solenopsis laurentia is represented in the Italian territory by the following subspecies:

Key to the subspecies of Solenopsis laurentia

1. Plant subacaule, stem 1.5–2.5 cm tall, flower pedicel 10–16 mm long, bracteoles 1–2 mm long............ S. laurentia subsp. parvula

- Plant erect to subcaulescens, stem 2.5–13 cm tall, flower pedicel (10)20–80 long, bracteoles 2–5 mm long ..................................2

2. Plant erect with solitary stem, only cauline leaves, calyx 3–4 mm long............................................................................................3

- Plant caespitose with several stems, leaves rosulate and cauline, calyx 4.1–5 mm long...................................................................4

3. Plant 8–13 cm tall, leaves 10–20 × 3–6 mm, calyx 3–4 mm long, corolla 5–6 mm long, papillae 0.12–0.30 mm long, 25–50 for each lobe, staminal filament 2.5–3.1 mm long........................................................................................ S. laurentia subsp. laurentia

- Plant 2.5–7.0 cm tall, leaves 3–10 × 1–3 mm, calyx 2.7–3.0 mm long, corolla 3.4–4 mm long, papillae 0.08–0.16 mm long, 5–10 for each lobe, staminal filament 2 mm long........................................................................................ S. laurentia subsp. gasparrinii

4. Plant up to 12 cm tall, calyx lobes smooth, corolla 4.5–5.0 mm long, papillae up to 0.3 mm long, 43–60 per lobe, anther tube without hairs on the back, capsule 3.5–4.0 mm long ........................................................................... S. laurentia subsp. caespitosa

- Plant no taller than 7 cm, calyx lobes with one small tooth per side, corolla 4.0– 4.2 mm long, papillae up to 0.16 mm long, 12–30 per lobe, anther tube with hairs on the back, capsule 3 mm long............................................................. S. laurentia subsp. hyblaea

Figures

FIGURE 1. Illustration of Lobelia laurentia Linnaeus published by Micheli (1729, Tab.14), lectotype of this species.

FIGURE 2. SEM micrographs of seed coat of Solenopsis laurentia subspecies. A. subsp. laurentia from Elba Island. B. subsp. gasparrinii from Contrada Anguillara (Sicily). C. subsp. caespitosa from Apulia. D. subsp. hyblaea from Sicily. E. subsp. parvula from Apulia: 1. whole seed (× 250). 2. Detail seed testa (× 1000).

FIGURE 3. SEM micrographs of pollen grains of Solenopsis laurentia subspecies. A. subsp. laurentia from Elba Island. B. subsp. gasparrinii from Contrada Anguillara (Sicily). C. subsp. caespitosa from Apulia. D. subsp. parvula from Apulia. E. subsp. hyblaea from Sicily: 1. Equatorial view (× 3000). 2. Polar view (× 3000).

FIGURE 4. SEM micrographs detail of pollen grains surface of Solenopsis laurentia subspecies (× 12000). A. subsp. laurentia from Elba Island. B. subsp. gasparrinii from Contrada Anguillara (Sicily). C. subsp. caespitosa from Apulia. D. subsp. parvula from Apulia. E. subsp. hyblaea from Sicily.