. Introduction

Portulaca L. (Portulacaceae Juss.) comprises over 100 species that are distributed worldwide (Mabberley, 2017; Plants of the World Online, 2022). Presently, this genus forms its own family (The Angiosperm Phylogeny Group, 2016; Nyffeler & Eggli, 2010), but in older classification systems, it has been combined with many other genera into a widely treated family of about 450 species (Carolin, 1993; Takhtajan, 2009). This genus occurs mainly in tropical and subtropical regions, particularly in Africa, South America, and the western regions of North America (Carolin, 1993; Takhtajan, 2009). However, the genus Portulaca is poorly represented in Eurasia.

In Poland, depending on the taxonomical point of view, this genus is represented by three or four species (Broda & Mowszowicz, 2000; Mirek et al., 2020; Rutkowski, 2011; Stengl-Rejthar, 1992; Szafer et al., 1988): P. oleracea L. (= P. oleracea L. subsp. oleracea), P. sativa Haw. [= P. oleracea L. subsp. sativa (Haw.) Čelak], P. grandiflora Hooker, and P. umbraticola Kunth. In recent studies, P. oleracea and P. sativa have been recognized as subspecies (subsp. oleracea and subsp. sativa, respectively) of P. oleracea (among others, Mirek et al., 2020; Rutkowski, 2011). Portulaca oleracea L. subsp. oleracea is an accidentally introduced and naturalized anthropophyte (kenophyte) (Mirek et al., 2020; Tokarska-Guzik et al., 2012). It occurs mainly in central-western (Wielkopolska) and south-western (Śląsk) parts of Poland (Zając & Zając, 2001), and is found in ruderal (among others, flower beds, roadsides, courtyards, garbage dumps, lawns, and railway grounds) and segetal (gardens, fields – mostly among root crops; sometimes as a troublesome weed) habitats (Mirek et al., 2020; Mowszowicz, 1986; Rutkowski, 2011; Stengl-Rejthar, 1992; Szafer et al., 1988; Tokarska-Guzik et al., 2012). Portulaca oleracea subsp. sativa has been reported from Poland only as a species cultivated as a vegetable (Broda & Mowszowicz, 2000; Mirek et al., 2020; Rutkowski, 2011; Stengl-Rejthar, 1992; Szafer et al., 1988).

Portulaca grandiflora Hook. was placed on a list of Polish ergasioephemerophytes (Rostański & Sowa, 1986–1987). This species was reported from Poland only once in 1932, from a rubble heap in Legnica (western Poland), as a possible escapee from cultivation (Schalow, 1933). It is cultivated in Poland as an ornamental plant (Rutkowski, 2011). Portulaca umbraticola has been reported from Poland only as a crop plant (“Portulaca umbraticola,” 2022).

The common purslane (Portulaca oleracea L.) is an interesting object of research in many different areas. In agricultural and ecological sciences, it has attracted attention as a common weed and invasive species in many European countries (among others, Protopopova & Shevera, 2019; Tokarska-Guzik, 2005; Tokarska-Guzik et al., 2012). In pharmaceutical sciences, it is a source of vitamins and antioxidants (among others, Liu et al., 2000; Oliveira et al., 2009; Simopoulos, 2004; Simopoulos et al., 1995; Simopoulos & Salem, 1986; Uddin et al., 2012, 2014). The genus Portulaca is also an interesting object of taxonomical studies, mostly due to its polyploidy (particularly within the Portulaca oleracea aggr.).

Recently, this aggregate has become an object of thorough investigation, started by Danin et al. (1978). It was found that it is a heterogeneous polyploid complex consisting of at least 9–19 microspecies or, according to other terminology, morphotypes (mainly autogamic) (among others, Danin & Anderson, 1986; Danin et al., 1978, 2008, 2012, 2014, 2016; Danin & Reyes-Betancort, 2006; Danin in Greuter & Raus, 2012, p. 291; Danin in Greuter & von Raab-Straube, 2011, pp. 131–134; Soltis & Soltis, 1999; Walter et al., 2015). The results of these studies and the narrow interpretation of taxa have stimulated further research on Portulaca oleracea aggr. in different countries and, consequently, led to the discovery of new taxa (among others, Bulakh et al., 2019; Domina & Raimondo, 2009; Feráková et al., 2012; Danin in Greuter & Raus, 2012, p. 291; Danin in Greuter & von Raab-Straube, 2011, pp. 131–134; Matthews et al., 1993; Rad et al., 2017; Rupesh et al., 2015).

The morphological features of seeds are important traits that enable differentiation between newly separated taxa. Based on the seed size and morphology of epidermal cells of testa, descriptions of new taxa and keys to their identification were prepared (Danin et al., 2008; Ocampo, 2013). Furthermore, Danin (in Greuter & von Raab-Straube, 2011, pp. 131–134), based on the analyzed material of P. oleracea s. l. from Poland (KOR), found several new Polish morphotypes (species): P. granulostellulata (Poelln.) Ricceri & Arrigoni, P. nitida (Danin & HG Baker) Ricceri & Arrigoni, P. trituberculata Danin, Domina & Raimondo and P. oleracea L. s. str. All of these taxa are of Mediterranean origin.

The aim of this study was to analyze the seed structure of herbarium specimens of P. oleracea agg. deposited in the Herbarium of the Department of Systematic and Environmental Botany of Adam Mickiewicz University in Poznań (POZ; https://amunatcoll.pl/), to identify new Polish taxa in the studied collection.

. Material and Methods

Herbarium specimens of P. oleracea aggr. from the POZ Herbarium of the Department of Systematic and Environmental Botany (formerly, Department of Plant Taxonomy) of Adam Mickiewicz University in Poznań were used in the present study (Table 1; https://amunatcoll.pl/).

Table 1

Herbarium specimens of Portulaca oleraceaaggr. deposited in the POZ Herbarium.

Species name on a herbarium labelLocalityHabitatSheet No.Date of collectionAuthor of collection
Portulaca oleracea L.Konin, Wielkopolska regionBy the bus station wallPOZ-V-000757811973-07Adamiak H.
Portulaca oleracea L.Będów near Krosno Odrzańskie, Lubuskie regionOdra River alluviaPOZ-V-000757861976-08-27Latowski K., Żukowski W.
Portulaca oleracea L.Stare Dymaczewo, Wielkopolska National Park, Wielkopolska regionRoadsidePOZ-V-000757771977-08-23Mikołajczak E.
Portulaca oleracea L.Railway station in Damasławek, Wielkopolska regionTrans-shipment siding trackPOZ-V-000757801975-09-30Latowski K.
Portulaca oleracea L.Railway station in Książ Wlkp., Wielkopolska regionBetween stone cobblesPOZ-V-000757751988-09-28Czarna A.
Portulaca oleracea L.Międzychód, Wielkopolska regionGravel by buffer stop of siding track, near railway stationPOZ-V-000757831970-09-30Hantz J.
Portulaca oleracea L.Środa Wlkp., Wielkopolska regionSiding track by ramp, opposite of railway stationPOZ-V-000757841970-08-02Hantz J.
Portulaca oleracea L.Bielany, Toruń, Kujawsko-Pomorskie regionOn sandy and gravelly ground by the playing-fieldPOZ-V-000757851979-09-20Ceynowa-Giełdon M.
Portulaca oleracea L.Czapury near Poznań, Wielkopolska regionNear compost heap along Warta RiverPOZ-C-00008262011-09-16Stachnowicz W.
Portulaca oleracea L.Wschowa, Wielkopolska regionRailway station at unused ramp, near station buildingPOZ-C-00009782000-09-01Latowski K.
Portulaca oleracea L.Krzyż, Wielkopolska regionRailway station, along the wall of station building on platformPOZ-C-00032111997-08-27Latowski K.
Portulaca oleracea L.Wschowa, railway station, Wielkopolska regionAt unused reloading rampPOZ-C-00033212000-09-01Latowski K.
Portulaca oleracea L.Closed railway line Czempiń-Śrem. Szymanowo, Wielkopolska regionOn railway trackPOZ-C-00033232003-07-20Nowak K.
Portulaca oleracea L.Leszno, railway station, Wielkopolska regionAlong the wall on platformPOZ-C-00033851997-09-09Latowski K.

In total, 14 seed samples (with 20 seeds each) were studied. The methodology used in this study follows that proposed by Danin et al. (1978, 2008, 2012), Danin and Raus (2012), Danin and Reyes-Betancort (2006), and Ocampo (2013), with modifications. The seed morphology, for example, the shape and peculiarity of the surface, was studied using a scanning electron microscope (SEM) at magnifications of ×100, ×200, ×400, ×800, and ×1,000. For the scanning electron microscope (SEM, JSM-6060LA), the seeds were fixed on the brass table, then, the samples were sputter-coated with gold according to the standard method used at the Center of Electron Microscopy of the M. G. Kholodny Institute of Botany, NAS of Ukraine. For size determination, 20 measurements were taken along the polar and equatorial axes for each specimen using AxioVision Rel.4.8 program.

The following seed traits were analyzed: shape, size and diameter, shape of the testa cell rays (Vr, Ur, Yr) (Figure 1), and shape of the periclinal walls (PCW). The terminology of Danin et al. (1978, 2012) was used to describe the seed surface ultrastructure of the morphotypes and the key for its determination (Figure 1). For the identification of taxa, a seed diameter limit (0.85 mm) was used, according to which the groups or separate morphotypes were differentiated. The nomenclature of the studied taxa follows Plants of the World Online (2022).

Figure 1

Morphological features of testa epidermal cells. Abbreviations: sr – short rays; lr – long rays, Ur – U-rays, Vr – V-rays, Yr – bifurcated rays.

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. Results

Seed morphology analysis in Portulaca oleracea aggr. shows that the analyzed material was very heterogeneous. It shows the differentiation between the studied samples (herbarium sheets) and within the samples when multiple specimens were mounted on a single sheet. The seeds from the studied samples differed in size. The diameters ranged from 0.672 to 1.1 mm. The epidermal cells of the testa were star-shaped, with periclinal walls (either smooth or papillated). Analysis of seed microphotographs obtained under a scanning microscope enabled the description of the detailed traits of the individual samples (Table 2).

Table 2

Identified taxa of Portulaca oleraceaaggr. deposited in the POZ Herbarium.

Sheet No.Taxon nameSeed length (µm)Rays VRays URays YLong raysShort raysCP pap.Ray pap. 1Ray pap. 2ID cellsEN cells
POZ-V-00075775P. nitida8400++++000++
POZ-V-00075777P. trituberculata9500++++++0++
POZ-V-00075780P. papillatostellulata9000++0+++++0
POZ-V-00075780P. granulatostellulata8000++0+++0+0
POZ-V-00075781P. trituberculata9500++0+++00+
POZ-V-00075783P. oleracea s. str.1,030+0+++000++
POZ-V-00075784P. oleracea s. str.930+0++0000++
POZ-V-00075785P. oleracea s. str.970+++++0000+
POZ-V-00075786P. daninii8500++0+++0+0
POZ-V-00075786P. macrantha1,0000+++++++++
POZ-V-00075786P. trituberculata9500++0++++0+
POZ-C-0000826P. oleracea s. str.920+++++0000+
POZ-C-0000978P. nitida8400+++0000+0
POZ-C-0003211P. nitida850+++++000++
POZ-C-0003321P. nitida850++++0000++
POZ-C-0003323P. oleracea s. str.840++++0000+0
POZ-C-0003385P. trituberculata9200++++++0++

[i] CP pap. – papillae in the central parts of rays; Ray pap. 1 – ray papillae rare (single); Ray pap. 2 – ray papillae frequent; ID cells – isodiametric cells; EN cells – elongated cells.

Based on the key for identification of Portulaca taxa according to seed traits presented in the article by Danin et al. (2008), the following taxa were distinguished: P. daninii, P. granulatostellulata, P. macrantha, P. nitida, P. oleracea, P. papillatostellulata, and P. trituberculata.

Portulaca daninii Galasso, Banfi & Soldano

The seed is subreniform, black, with a glossy surface; the seeds are <0.85 mm in diameter and range from 0.672 mm to 0.823 mm (with an average of 0.819 mm). The individual cells were mostly elongated and isodiametric, mainly convex or domed, with tubercles in the center of the cells and papillae at the ends of some rays (Figure 2). The specimen examined originated from the Odra River alluvia in the vicinity of Krosno Odrzańskie (POZ 00075786; Table 1).

Figure 2

Portulaca daninii (SEM). General view of the seed (A). The seed surface (B,C). Isodiametric cell (C1), elongated cell (C2); general view of the cells (D,E).

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Portulaca granulatostellulata (Poelln.) Ricceri & Arrigoni

The seed is subreniform, black, with a glossy surface; the seeds are <0.85 mm in diameter and range from 0.703 mm to 0.849 mm and 0.733 mm on average. The individual cells of the surface are star-shaped and elongated, convex, nearly flat to low-convex; the length of the rays exceeds the width 1.5–2 times. The cells were papillated, with papillae located at the ends of the cell rays or on a few cells at the base of the rays (Figure 3). The examined specimen originated from the Damasławek railway station, Wielkopolska Province (POZ 00075780; Table 1).

Figure 3

Portulacagranulatostellulata (SEM). General view of the seed (A). The seed surface (B,C). Isodiametric cell (C1), elongated cell (C2); general view of the cells (D,E).

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Portulaca macrantha Ricceri & Arrigonii

The seed is subreniform, black, with a glossy surface; the seeds have a diameter of >0.85 mm and range from 0.850 mm to 1.03 mm; 0.916 mm on average. Individual cells on the surface were isodiametric and elongated. The testa cells are star-shaped, convex, or domed; the rays are short, with terminal papillae on the rays and two–seven scattered small tubercles or papillae in the center (Figure 4). The specimen examined originated from the Odra River alluvia in the vicinity of Krosno Odrzańskie (POZ 00075786; Table 1).

Figure 4

Portulaca macrantha (SEM). General view of the seed (A). The seed surface (B,C). Isodiametric cell (C1), elongated cell (C2); general view of the cells (D,E).

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Portulaca nitida (Danin & H. G. Baker) Ricceri & Arrigoni

The seeds are subreniform or rounded, black, with a glossy surface; the seeds are <0.85 mm in diameter and range from 0.691 mm to 0.848 mm, 0.808 mm on average. The individual cells were isodiametric, star-shaped, or elongated, with long rays, nearly flat to slightly convex, and without papillae and tubercles (Figure 5). The specimens examined originated from Książ Wlkp. (POZ 00075775), Wschowa (POZ-C-0000978, POZ-C-0003321) and Krzyż (POZ-C-0003211) railway stations (Table 1).

Figure 5

Portulaca nitida (SEM). General view of the seed (A). The seed surface (B,C). Isodiametric cell (C1), elongated cell (C2); general view of the cells (D,E).

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Portulaca oleracea L. s. str.

The seed is subreniform or rounded, black, with a glossy surface; the seeds are approximately 0.85–1.1 mm in diameter and range from 0.812 mm to 1.076 mm; 0.943 mm on average. The individual cells were star-shaped, isodiametric, or elongated, mostly flat, with long rays, smooth, and without papillae and tubercles (Figure 6). The specimens examined originated from: Międzychód (POZ 00075783) and Środa Wlkp. railway stations (POZ 00075784), railway tracks in Szymanowo (POZ-C-0003323), a sandy playing field in Toruń (POZ 00075785), and in the vicinity of a compost heap along the Warta River (POZ-C-0000826) (Table 1).

Figure 6

Portulaca oleracea s. str. (SEM). General view of the seed (A). The seed surface (B,C). Isodiametric cell (B1), elongated cell (B2); general view of the cells (D,E).

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Portulaca papillatostellulata (Danin & H. G. Baker) Danin

The seed is subreniform, black, with a glossy surface; the seeds are approx. 0.85–1.1 mm in diameter and range from 0.857 mm to 0.922 mm; 0.883 mm on average. The individual cells were star-shaped, isodiametric, and elongated; the central parts of the cells are convex or nearly flat to low-convex, smooth, without papillae, with long rays, many with terminal papillae, but not all were papillated; some papillae were more inflated than the cell bodies (Figure 7). The examined specimen originated from the Damasławek railway station (POZ 00075780; Table 1).

Figure 7

Portulaca papillatostellulata (SEM). General view of the seed (A). The seed surface (B,C). Isodiametric cell (C1), elongated cell (C2); general view of the cells (D,E).

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Portulaca trituberculata Danin, Domina & Raimondo

The seed is subreniform, black, with a glossy surface; the seeds are approx. 0.85–1.1 mm in diameter and range from 0.857 mm to 1.03 mm; 0.931 mm on average. The individual cells were star-shaped and elongated; the central cell parts were convex or nearly flat to low convex, smooth, without papillae, with long rays, many with terminal papillae but not all were papillated, and papillae were more inflated than the cells (Figure 8). The specimens examined originated from the Konin (POZ 00075781) and Leszno (POZ-C-0003385) railway stations, roadsides in the Wielkopolski National Park (POZ 00075777), and the Odra River alluvia in the vicinity of Krosno Odrzańskie (POZ 00075786) (Table 1).

Figure 8

Portulaca trituberculata (SEM). General view of the seed (A). The seed surface (B,C). Isodiametric cell (C1), elongated cell (C2); general view of the cells (D,E).

https://www.journalssystem.com/asbp/f/fulltexts/159569/Figure_8_min.jpg

. Discussion

Among the 39 herbarium specimens, denoted as P. oleracea and deposited in the POZ Herbarium (Vascular Plant Collection, POZ-V; https://amunatcoll.pl/), only eight sheets contained seeds. Additionally, there were six samples of P. oleracea seeds in the carpological collection (POZ-C; https://amunatcoll.pl/). Fourteen seed samples were analyzed in total. All originated from central-western Poland (Wielkopolska Province). In this area, there is the highest concentration of P. oleracea localities in Poland (cf. Zając & Zając, 2001; https://amunatcoll.pl/).

Previously, four taxa have been distinguished within Portulaca oleracea aggr. in Poland: P. granulatostellulata, P. nitida, P. trituberculata, and P. oleracea s. str. (Danin in Greuter & von Raab-Straube, 2011, pp. 131–134). Micromorphological analysis of the seed surface ultrastructure of P. oleracea aggr. material deposited in the POZ Herbarium, which was conducted as a part of this work, enabled the documentation of seven morphological types. Apart from those previously reported by Danin (in Greuter & von Raab-Straube, 2011, pp. 131–134), other morphotypes (species) are new records for Poland. They include P. daninii, P. macrantha, and P. papillatostellulata. Presently, there are 10 taxa of the genus Portulaca in the flora of Poland, seven of which have been distinguished within P. oleracea aggr. (Danin in Greuter & von Raab-Straube, 2011, pp. 131–134; Mirek et al., 2020; Rutkowski, 2011).

The most frequently identified taxa were P. oleracea L. s. str. (five samples), and P. trituberculata and P. nitida (four samples each) (Table 2), respectively. They mostly originated from railway areas (stations and tracks) and ruderal places (playing field and roadside), and less frequently from alluvial areas. These observations confirm that the taxa of P. oleracea aggr. mostly migrate to plant communities that develop in anthropogenic habitats (Tokarska-Guzik et al., 2012).

The nearest localities of the taxa documented in this study were observed in neighboring countries, such as Germany (P. nitida), Slovakia (P. granulatostellulata, P. papillatostellulata, P. trituberculata), Ukraine (P. granulatostellulata, P. papillatostellulata) and Belarus (P. granulatostellulata, P. nitida, P. oleracea s. str., P. trituberculata) (Bulakh et al., 2019; Feráková et al., 2012; Danin in Greuter & von Raab-Straube, 2011, pp. 131–134; Dzhus et al. in von Raab-Straube & Raus, 2015, pp. 457–459). Two out of the three new taxa distinguished for Poland in this study – P. macrantha and P. tuberculate, are also new records for Central and Eastern Europe.